DIY Attic Insulation has over 60 pages of information on buying and installing attic insulation and sealing air leaks in the attic floor, for homeowners who are handy!


Does Your Attic have Enough Insulation?
Fiberglass Batt Insulation vs Cellulose Loose Fill vs Spray Foam
Radiant Barrier Insulation
Insulate the Roof
Insulate an Attic Floor
Seal the Air Leaks in the Attic Floor
Insulate the Knee Walls
Insulate the Attic Walls
Other Places in the Attic to Insulate
Cover Recessed Lights and Other Fixtures With Air-Tight Covers

Adding insulation to your roof and attic floor and sealing the air leaks in your attic floor is likely to be the best investment you could make to lower your utility bills, and if you are handy you can do it all yourself. If you insulate the attic floor you will lower your air conditioning costs probably much more than you had expected, because when the attic is very hot, much heat radiates downward to the floor below.

The shingles and roof become extremely hot on hot, sunny days, so insulation mounted under the roof prevents much of this heat energy from entering the house and increasing the home’s demand for air conditioning. Also, most unfinished attics have air temperatures of over 100° for much of the summer and the insulation on the attic floor prevents much of this heat energy from entering the living space below.

In the heating season, most attics become cold due to outside air entering through the soffit vents and leaving through gable vents, a ridge vent, or roof vents. The soffit vents are either on the attic floor close to the roof or beyond the floor at a lower level in a soffit overhang.

Insulation on the attic floor prevents much of the heat energy in the living space below to pass into the attic through conduction and radiation, raising your heating costs

You must seal the leaks in your attic floor, such as those around the light fixtures, to thoroughly insulate your attic. These air leaks can greatly increase your heating and air conditioning costs if you have ceiling fans, ceiling lights, or recessed lights that allow pathways through the ceiling. Any attic could be better insulated, either because there are places that aren’t insulated, such as the backs of the “knee walls”, or because the ceiling or floor insulation is too thin, or because there are places where air leaks through the attic floor.

You can add insulation in many places, whether the attic is finished (has walls and ceiling similar to those of the other rooms of your house) or is unfinished. If it is finished, you can put insulation on the back of the knee walls if none is there. These are short walls, normally on two sides of a finished attic. They have either access panels or small doorways to crawl through.

You can probably add extra insulation to the floor behind the knee walls. If your attic is finished you can blow loose fill insulation into the space above the ceiling if there is little or none there. This is a do-it-yourself job; you rent the blower, and the space above the ceiling is easily accessible from behind the knee walls.

Insulating your roof should also prevent ice dams from forming. They are created when heat from the attic passes through the roof, melting the snow on the roof. The water flows down to the gutters where it re-freezes to form a dam. The dam traps water on the roof, which may drip into the house, causing mold and mildew in the house and damaging the plaster or drywall. The snow shouldn’t melt if the roof is well-insulated

This web page describes and compares the types of insulation currently used to insulate attics: fiberglass batt insulation, cellulose loose fill insulation, spray foam insulation, and radiant barrier insulation.

Does Your Attic Have Enough Insulation?

Would it be a good investment to add insulation in your attic? This depends on many factors, such as whether you would do the work yourself or hire a contractor; whether you have whole house air conditioning; what type of heating fuel do you use; whether you expect the cost of your heating fuel or electricity for your air conditioning to increase greatly while you own the home; and whether you buy the insulation on sale.

You can buy fiberglass batt insulation at a greatly reduced sale price at times of the year. Is it windy where you live? This raises your heating costs because a strong wind draws warm air out of the attic vents. Do you want to make an investment in insulation that would pay for itself in five years, ten years or twenty years?

The EPA article, “Recommended Home Insulation R-Values” shows a map of 8 climate zones in the United States, with a table showing the EPA recommended R-values for retrofitting the walls and attics of wood-framed buildings with insulation in each zone. See Recommended Home Insulation R-values The map and the recommended R-values for attics are shown below. The many factors given above show that your home may need very little or very much insulation, so the EPA’s recommended R-value may not be right for your home.

insulate an attic floor
Recommended Insulation Levels for Retrofitting Existing Wood-Framed Buildings

In the table below, the R-value indicates how well a material or a roof or wall or floor resists heat flowing through it. It is given in ft²-deg-hr/Btu. It is the Btu’s that would pass through each square foot per hour for each degree of temperature difference. The R-value of a roof or an attic floor is very roughly the sum of each material that heat must pass through.

ZoneUn-Insulated AtticExisting 3-4 Inches of InsulationAttic Floor

A reflective surface on the roof or attic floor blocks thermal radiation and thus increases that surface’s R-value. Many insulation products have R-values given on their labels, but the increase in R-value they give to a surface depends on how they are used. For example, they create a much higher R-value if mounted with a space next to their reflective surface. Recommended Insulation Levels for Retrofitting Existing Wood-Framed Buildings The R-values below are taken from “Recommended Home Insulation R-Values”.

The R-values given are for retrofitting. This is adding insulation to an existing home. The range of R-values for the Washington, DC zone, for example, is R-38 to R-60. This is 12” to 20½” of fiberglass batt or roll insulation. The rafters are 2×10’s in a typical home. If a roof in Washington has 6½” thick fiberglass insulation, which allows a space of 3″ above it for airflow, the chart indicates that between 5½” and 14” of insulation should be on the attic floor.

If your attic is finished, you can add insulation to the areas of roof and floor that are behind the “knee walls” to give this area the recommended R-value. The knee walls are the two short walls that are normally on opposite sides of a finished attic. You can also blow in loose fill insulation above the ceiling. This is a do-it-yourself project. It is described in the topic below, Insulate the Roof

With so many factors, it is impossible to calculate the optimum thickness of insulation that your attic should have. Fortunately, however, there is often a convenient amount of insulation to add. For example, if your attic floor is only about half full of loose fill insulation, which is often because the insulation settled, it is convenient to fill to the top of the rafters (the beams that hold up the roof). If you would add more than that it would be hard to use the attic for storage .

If your roof is insulated and your climate is not very cold, this may be a good place to stop adding insulation. If the spaces between the rafters and the spaces between the floor joists are filled, and your air conditioning costs are high, you could lower your air conditioning bills by stapling sheets of radiant barrier insulation across the bottom of the rafters, see Radiant Barrier Insulation.

Fiberglass Batt Insulation vs Cellulose Loose Fill Insulation vs Spray Foam Insulation

“Fiberglass batt insulation”, as it is normally called, is available in batts and continuous rolls. The batts are 48” or 93” long with about six in a package. There is no difference between fiberglass insulation in batts and in rolls. Batts are more convenient to use if the insulation is very thick.

Fiberglass batt insulation is sold in only two widths, 15½” for 16” on-center stud spacing, and 23½” for 24” on-center stud spacing. “Faced” and “un-faced” rolls and batts are available for most R-values. Faced rolls and batts have Kraft paper facing. This is a vapor barrier. It is stapled to rafters or wall studs to hold in the insulation.

Insulation of these R-values is available at home centers. Different brands can have slightly different thicknesses and R-values.

Insulation Thickness Typical R-Value
3 1/2"R-13
6 1/4" - 6 1/2"R-19
9"-10 1/4"R-30

Cellulose loose fill insulation, which is also called “cellulose blow-in insulation” is made from recycled paper treated with flame retardant. It has the highest R-value of all common types of loose-fill insulation and is the only type sold at most home centers. It is less expensive than fiberglass batt insulation but has a significantly lower R-value.

It can be used to cover the floor in an unfinished attic. You could do this either with a rented insulation blower or by spreading it by hand with an 18″ push broom. It is often used to add 1″ or 2″ of insulation when the existing insulation is very old and has settled. Also, it is the only good way to insulate the ceiling above a finished attic. You must blow it in between the ceiling and the roof using a rented insulation blower.

how do you insulate an attic?
. Roof Insulated with Spray Foam

Spray foam insulation is the most expensive of these, but it provides the highest R-value. It is not applied by do-it-yourselfers because it requires training to apply. The labor cost is high and also the material cost. It is widely used in very cold climates and in homes with truss ceilings. It is used on truss ceilings because these normally have 2″x6″ boards at the top, which would allow only R-13 fiberglass insulation.

Thicknesses Required for Insulation of R-38

There are two categories of spray foam insulation used in attics: open cell and closed cell. Both of these are both made from icynene. Closed cell insulation is more expensive. It is commonly used to insulate roofs because it creates a very good vapor barrier

There are risks in hiring a contractor to install spray foam insulation, mainly because it requires training to apply. If it is poorly installed it can contract and pull away from the rafters, leaving gaps. If the contractor may also put it on too thin to cut costs. The drawing compares the thicknesses of R-38 insulation for the three common attic insulation materials.

Radiant Barrier Insulation

Radiant barrier insulation is made of heavy paper covered by a shiny metallic surface on one or both sides. It insulates by reflecting infrared radiation, which is one of the ways heat energy is transmitted. Much of the attic’s heat escapes in winter through infrared radiation in an unfinished attic. It is most cost-effective if you have air conditioning ducts in the attic because it keeps the attic and the ducts cooler in the summer.

If radiant barrier insulation is mounted to the bottom of the rafters with a reflective surface facing downward, it blocks much heat from escaping in the winter. In the summer, when the attic is extremely hot, a reflective surface facing downward traps heat in the attic. However, if the reflective surface is facing upward, much of the heat energy in the roof is blocked from entering the attic. This will increase your air conditioning costs. Roofs can be as hot as 150° in hot, sunny climates and pass much heat energy down into the attic.

Use “double reflective” radiant barrier insulation to block the radiation in summer and winter. This has reflective material on both sides. Radiant barrier insulation must be mounted very tightly to the bottoms of the rafters or trusses to block convection, i.e. air flowing between the rafters or trusses and the insulation.

Some studies have shown that radiant barrier insulation can reduce air conditioning costs by 5% to 10% in warm, sunny regions of the country. The savings will be less in a cloudy climate because the roof becomes much less hot. If you have central heating and central air conditioning and your air conditioning costs are much lower than your heating costs, it would probably be a better investment to add extra fiberglass batt insulation than to mount a radiant barrier.

How to Mount Radiant Barrier Insulation

        1. Before mounting radiant barrier insulation, carefully inspect the rafters and insulation for signs of water damage, and repair the roof where it has occurred.
        2. Follow the manufacturer’s instructions.
        3. Use ¼” or 5/16” staples.
        4. Wear a respiratory mask and light the attic well, with trouble lights if necessary, to prevent you from stepping on cables, phone lines or low-voltage wiring.
        5. If it will be mounted to the bottom of the rafters or trusses with its reflective surface facing upward, and the roof is insulated with fiberglass batts or rolls, there must be a gap between it and the fiberglass insulation. If it contacts the insulation it will not reflect radiation. Staple the radiant barrier insulation on loosely, draped between the rafters or truss boards, to create gaps.

Insulate the Roof

      • If there is a ridge vent at the top of your roof, do not block the pathway along the roof from the soffit vents to the ridge vent. On some days, air flows in through the soffit vents and out through the ridge vent, drawing out air from all over the attic. This flow of air out of the attic is necessary because this air contains much moisture, and moisture damages sheathing and wood framing.

        1. There are several methods of adding additional roof insulation when the spaces between the rafters are filled with insulation.
        2. Mount a layer of batt insulation crossways to the rafters. The batts can be stapled on, but you must first cut long slashes in the existing Kraft paper. This will prevent water vapor from being trapped between the existing Kraft paper and the new Kraft paper.
        3. Staple radiant barrier insulation across the rafters and let it hang loosely to create a gap above it.
        4. Screw 2″x 2″ boards to the bottom surfaces of the rafters. This will give rafters with nominal dimensions of 2″x 10″, for example, nominal dimensions of 2″x 12”, allowing for more insulation. Use 3 ½” thick fiberglass batt or roll insulation. This is the thinnest size available. You must first cut long slashes in the existing Kraft paper to prevent trapping water vapor between this and the new Kraft paper.

      • Screw on boards to add insulation if you plan to cover the roof with drywall to make a finished attic, or at least leave open this option. If your climate is very cold, significant heat is lost from the attic by conduction through the rafters. Adding a layer of fiberglass insulation crosswise to the rafters will prevent most of this heat loss.

      • In very cold, humid climates, some contractors cover the insulation with plastic sheeting as a vapor barrier. This is done to prevent any air from leaking past the Kraft paper, reducing its effectiveness, and also because this leakage could cause harmful condensation. Plastic sheeting also increases the R-value of the roof’s insulation, especially if a gap is left between the plastic sheeting and the batt insulation, by letting the sheeting sag slightly.

        Plastic sheeting is sold in 10′ x 100′ rolls, so very little air will leak through it if mounted carefully. It is sold at home centers and paint stores. You could ask at your local building supply store or ask a building inspector if it is advisable to use it where you live.

      • If your roof is built from trusses, it will normally have 2”x6” boards as the top members of the trusses. Many homeowners hire an insulation contractor to insulate a truss roof with spray foam insulation if the roof has no ridge vent at the top, but this is much more expensive than fiberglass batt insulation and it is not a do-it-yourself project. Spray foam should not be used if there is a ridge vent because it will block the path from the soffit vents to the ridge vent.

      • If you will mount fiberglass batt insulation and your roof has a ridge vent, use 3½” thick rolls or batts and allow a gap of 2” above the insulation, or mount attic baffles to the roof and use 5½ “ thick insulation. Both options allow the necessary pathway from the soffit vents to the ridge vent. Both also insulate by preventing much of the heat transfer between the roof and the insulation.

        Attic baffles are installed by “friction fit” so they don’t need to be stapled on. Attic baffles, also called “attic ventilation channels” are very inexpensive. They are sold at home centers.

      • If your roof is insulated with fiberglass batts or rolls, there should either be a gap between the insulation and the roof, or baffles next to the roof. It is necessary to have one or the other because they allow a pathway from the soffit vents for air to enter the attic. They also insulate by preventing heat from being conducted between the insulation and the roof. If there is no gap, pull the staples and remove the insulation without tearing the Kraft paper. If it is torn, air will pass through it in a convection cycle, as explained above.

        Mount attic baffles to cover the entire roof. They “friction fit” into place and don’t need to be stapled in. Staple the insulation back on. Attic baffles, also called attic ventilation channels, are inexpensive.

      • If your roof is flat, the attic may be a few feet high at the front of your house and only about a foot high at the back. At the back there may be no insulation in the roof because the installer found it too hard to work there. Check for this and try to install insulation there if it is missing.

      • Before adding insulation to the roof, inspect the rafters or truss members, and the roofing if it is uncovered, for stains. These could indicate current rain leaks or leaks from years past. They must be repaired if they are current.

      • If you will be removing old insulation, check if it is made from asbestos if you are unsure. You can find an independent testing lab by doing an internet search of “asbestos testing labs”.

      • If your home was built in the very early twentieth century, when few homes had electric service, the attic could have “knob-and-tube wiring”. This has black insulation and is strung between porcelain insulators nailed to the ceiling joists or rafters, which prevent the wiring from contacting the wood. Do not cover this wiring with insulation. It must release heat into the air to avoid overheating. If it is covered with attic insulation it could overheat and its insulation could burn.

      • If your roof is insulated with fiberglass batt insulation, check if the Kraft paper is mounted tightly to the joists to prevent air from leaking through. If it is loosely mounted, on hot, sunny days the air close to the roof becomes very hot and flows into the attic through these gaps due to convection. It is replaced by air from the attic in a convection cycle. On cold days the air close to the roof becomes cold and flows into the attic through these gaps. Also, convection brings water vapor which dampens the insulation, making it much less effective.

How to Mount Fiberglass Batt Insulation to the Roof


        • Batts or rolls of fiberglass insulation
        • Two staple guns
        • 5/16” or ¼” staples to mount batts between the rafters
        • 9/16″ staples to mount batts crossways to the rafters
        • Two respirators or dust masks
        • Trouble light and 50-ft. extension cord if attic not well lit
        • Large scissors
        • 10’x100′ roll of 4 or 6 mil plastic sheeting if this will be used
        • Attic baffles to cover the roof if these will be used

The insulation must be Kraft faced, labeled “Faced”. Buy batts or rolls that are the width of the spaces between the joists, either 15” or 23”. If you buy 6½” thick insulation, which is R-19 or close to this, the labels may be misleading because they may say, “for 2×6 walls and or for floors”. If you have rafters and you will not put up baffles, buy insulation that is less thick than the depth of the rafters, to leave a gap between the insulation and the roof. The thickness you need is explained above in the topic, Does Your Attic Have Enough Insulation?.

When buying insulation, you may not need to calculate how many rolls you will need. Buy enough insulation to fill your car, van or pickup truck, and install this. It may, for example, cover 60% of your roof if you have a van or pick-up truck. Then you can count how many rafters or trusses have been insulated and how many have not been insulated, and easily calculate how many more batts or rolls to buy.

Fiberglass insulation for attics is sold in continuous rolls and also in 93” and 48” batts. The material is the same in either form. Do not use batts or rolls that are too thick if only these are available, because compressing them to fit into the spaces lowers their R-value.

Batt insulation can be mounted to the rafters in either of two ways:

      • Mounted between the rafters with the Kraft paper stapled to the bottom surfaces of the rafters. This method of installation allows you to use thicker batts. A space of 1″ or greater must be left above the batts for air to flow to the soffit vents.

      • Mounted between the rafters with the Kraft paper stapled to the sides of the rafters, allowing a space above and below them. This allows you to achieve a much higher R-value by mounting 4’x8’ sheets of rigid insulation or by stapling on radiant barrier insulation, which is heavy paper with a reflective surface, or by mounting a second layer of batt insulation crossways to the rafters. See Radiant Barrier Insulation.

        As explained in “Radiant Barrier Insulation”, the space above radiant barrier insulation is necessary for the insulation to block heat from entering the attic on hot summer days. If a second layer of batt insulation is added, the space is effective dead air insulation. There are many rigid insulation products to choose from, but they are all much more expensive and require far more time to mount than radiant barrier insulation, which you simply unroll and staple on.


        1. Do not work on a hot day. The attic temperature would be over 100° if the attic is uninsulated.

        2. Work with another person. One person will hold one end of each piece of insulation while the other person pulls the other end tightly and staples it on. Also, one person can pass the pieces of insulation up to the person in the attic.

        3. Light the attic well to prevent stepping on wires or cables. If necessary, use clamp-on trouble lights.

        4. Wear gloves, a long sleeve shirt and goggles.

        5. Be very careful not to step between the floor joists or truss members. The surface you see there is the ceiling of the room below and if you step on it you will break it.

        6. If the batts or rolls are the thickness of the rafters (normally 7½”) or the truss members (normally 5½”), mount attic baffles to cover all of the area that will be insulated before mounting the insulation. Staple them on with the staples used for the batts.

        7. If you are adding the insulation to existing insulation, either between the rafters or crossways, you must make many cuts in the existing Kraft paper. If you don’t, vapor will be trapped in the new insulation, making it less effective and possibly soaking and damaging the rafters. If you are adding the insulation crossways, use the longest size available, which should be 9/16″.

        8. Mount the insulation by stapling its Kraft paper to the rafters or trusses. If you will be mounting radiant barrier insulation to the rafters after you have mounted the fiberglass batts, and with its reflective surface facing upward, staple the Kraft paper to the sides of the rafters, about an inch above the bottom edges of the rafters. This will allow space between them and the radiant barrier.

          Staple the Kraft paper on tightly with no gaps between it and the rafters or trusses. You could instead mount the radiant barrier very loosely so it sags to leave a gap, but it would be less effective mounted this way.

        9. If there is a ridge vent at the top of the roof, do not cover it with insulation. A ridge vent appears from in the attic as a thin gap along the top of the roof, where two roof surfaces meet.

        10. If your attic is finished and you are insulating the roof outside of the knee walls, do not block the spaces above the knee walls. If there is no ridge vent, these spaces are pathways for hot air above the attic’s ceiling to flow down to the soffit vents. If there is a ridge vent, they allow air to flow up to it.

        11. If mounting a layer of batts crossways to the joists, don’t allow gaps between adjacent batts. Where two batts meet, close one paper tab and open the other so that the tab rests on the adjoining batt to block airflow.

        12. Leave a few inches of space where the floor meets the roof to avoid blocking the airflow through the soffit vents. The soffit vents may be on the attic floor or may be in a “soffit overhang” where they aren’t visible from the attic.


        • Trouble light and long extension cord if the attic is not well lit
        • Gloves, long sleeve shirts, goggles
        • Batts or rolls of fiberglass insulation
        • Two heavy duty staple guns with box of ¼” or 5/16″ staples 
        • Box of 9/16″ staples if insulation will be mounted cross-wise. 

How Do You Insulate an Attic Floor?

If your attic is unfinished and the attic floor has no floorboards, fill the spaces between the joists or the bottom members of the trusses with insulation. This is an easy do-it-yourself project. This will reduce your the home’s use of air conditioning significantly because without insulation the ceilings of the rooms on the top floor become hot when the attic is hot.

The ceilings radiate heat into the rooms, increasing the need for air conditioning. In winter, air enters the attic through the soffit vents, heats and expands and exits through the roof vents, gable vents or ridge vent, which are all higher. This air flowing through the attic can make the attic cold on very cold days. If the attic floor has no insulation, much heat is lost from the living space below through heat flowing up through the floor.

. Heat Flowing Through Uninsulated Attic Wall

Homes built in the early twentieth century and earlier used a variety of materials as loose fill insulation on attic floors, and in many homes those materials are still in use. Some of these materials should be removed because they are poor insulators. Probably all of the materials that were used before fiberglass batt insulation and loose fill cellulose are relatively poor insulators. Also, many of these materials are flammable, such as sawdust and rags, which were occasionally used on very old homes.

Some homes have asbestos insulation on the attic floor. If the insulation could be asbestos, you must test it to find out. You can find an independent testing lab by doing an internet search of “asbestos testing labs”. It must be removed by an asbestos abatement company. Unlike asbestos siding, which is not unsafe, asbestos loose-fill attic insulation is unsafe because persons could walk on it and stir it up, putting particles into the air.

      • Check if there is a different type of insulation buried beneath the insulation you see if your home is very old. You may wish to remove it.

      • There are two materials which a do-it-yourselfer can use to insulate an attic floor: cellulose loose fill insulation and fiberglass batt insulation. These are described in the section, Fiberglass Batt Insulation vs Cellulose Loose Fill vs Spray Foam These have the shortest return on investment and are probably the only types of insulation for attic floors sold at your local home center or builders’ supplies.

        Cellulose loose fill insulation has a higher R-value than fiberglass batt insulation and is less expensive. It takes much more work to put down because you must block it from covering the soffit vents, ceiling fans, bathroom exhaust fans, recessed lights, and electrical boxes for ceiling lights. The ways to do this are described below. Also, it can fall through a hatchway when you enter the attic.

        To use fiberglass batt insulation, you only need to lay down the batts or rolls, keeping a space between them and the fixtures and the soffit vents.

      • Check if your attic floor has batt insulation with Kraft paper at the top. If so, turn the insulation over. This is a serious mistake which is occasionally made.

      • If your attic becomes very cold in winter because you have two gable vents that allow a strong flow of cold air into and out of your attic, add extra insulation the floor. This insulation should be a better investment than putting up the same thickness on the roof as extra insulation.

      • If you have water pipes in your attic, which is very unlikely because it is not permitted by code, you should not insulate the floor without also insulating the ceiling. Insulating the floor without insulating the ceiling could result in the attic temperature falling to below freezing, due to air flowing into and out of the attic through the vents. The water in the pipes could freeze and rupture the pipes. Insulating the pipes does not guarantee that they will never freeze.

      • If your roof is built from trusses and you will lay thick insulation on the floor, do not use batts that are so thick that you cannot easily see the floor joists. If you accidently step between the floor joists you will break the ceiling below.

      • If you live in a relatively cold climate, there is a problem with laying thick insulation on the attic floor and having no insulation on the roof. On very cold days when the sun is shining brightly, the roof will be hot from solar radiation and the air in the attic will be cold.

        The cold attic air contacting the warm roof will cause condensation to form on the roof. Mold and mildew may form, and in severe cases wooden beams will rot. Mold and mildew release spores, which can be especially harmful to persons with allergies and respiratory problems, and to the elderly.

      • If you use your attic for storage and you are adding a layer of insulation above the floor joists, whether the attic is finished or unfinished, you could build a surface above the floor which is large enough to support the stored items. Build the storage area in sections of 4′ by 8′. For each section buy 2” thick boards of a width greater than the thickness of the new insulation, to support the new surface. For example, if you will lay 6½” insulation, buy 2”x8” boards.

        Buy ½” interior plywood for the top surface. This is sold in 2’x4′ and 4’x4′ pieces. If there are floor boards, you could take them up and use them to build the new surface. For each 4′ by 8′ section:

        1. Cut the 2” thick boards into seven 4 ft. pieces.
        2. Cut six 4 ft. pieces of insulation and remove its Kraft paper.
        3. If 2’x4′ or 4’x4′ pieces of plywood will be used, you don’t need to cut them.
        4. If boards will be used, cut them to 8 ft. lengths.
        5. Set the seven 2” boards on edge, crosswise to the floor joists, and put the pieces of insulation between them.
        6. Lay the plywood or boards over them and screw them tightly onto them to form a 4’x8′ surface.
        7. Build more sections if you need them.
        8. Cover the remainder of the floor with batt insulation.

How to Lay Fiberglass Batt Insulation or Loose Fill Cellulose Insulation on the Attic Floor


Hardware Cloth

        1. If fiberglass batts or rolls will be used: 1) buy un-faced batts or rolls if you are adding to existing insulation. If this is not available, buy faced insulation and tear off the Kraft paper. 2) buy faced batts or rolls if not adding to existing insulation.
        2. Clamp-on trouble lights with extension cord.

        3. Large push broom if using loose fill insulation. (a rake may snag wiring).

        4. Large scissors to cut insulation batts or cut open bags of loose fill insulation.

        5. Metal hardware cloth to build fences around fixtures and 1” thick boards of the width of the floor joists to block the insulation from the soffit vents, but only if loose fill insulation will be used.

        6. Bags of cellulose loose fill insulation or batts or rolls of faced fiberglass insulation. The width of the batts or rolls must be the distance between the floor joists or the attic trusses. Floor joists are always 16” apart and attic trusses are normally 24” apart.

        7. Rented insulation blower for loose fill insulation (not necessary)

There is “itch-free” fiberglass batt insulation for persons sensitive to fiberglass insulation. There is also insulation wrapped in plastic wrap to prevent fiberglass from getting into the house. This should not be laid over existing insulation because the plastic wrap would trap water vapor.

Instead of estimating how many bags of loose fill insulation or how much fiberglass insulation to buy, it is much easier to buy as many bags as your vehicle will hold, lay the insulation and then estimate how much more to buy.


        1. Wear a respiratory mask, gloves, a long sleeve shirt and goggles.

        2. Light the attic well to prevent stepping on wires and cables. If necessary, use clamp-on trouble lights.

        3. Carefully inspect all house wiring (120-volt cables) that will be buried by insulation. Check for frayed insulation; cables that are connected with no junction box (open splices); cables entering a junction box that are not anchored to it with clamp connectors; and cables not stapled to the floor close to the junction box. These are fire hazards.

          Cables that are connected with no junction box or in a junction box but not anchored to it could easily become unconnected if kicked. If there are non-metallic cables, such as “Romex cables” that are connected with no junction box, buy a small metal electrical box, a cover for it, and a 3/8” cable clamp connector for each wire. These may be called “3/8″ non-metallic clamp converters”.

        4. If you find cables that are connected in a box but not anchored to it with cable clamps, buy a 3/8” non metallic cable clamp connector for each wire.

        5. To fix either problem, turn off the power to that circuit. Use a voltage tester to check if the voltage is off, and turn off the circuit breakers for the top floor one by one at the circuit breaker panel until the tester light indicates that the power is off.

          Disconnect the cables and reconnect them in the electrical box, anchored by the cable clamp connectors. Use “electricians plyers” to re-connect the wires.

        6. Be very careful not to step between the floor joists or the attic trusses if there are no floorboards. The surface you see is the ceiling of a room below and if you step on it you will break it.

        7. If you are laying batts or blankets on a floor that has no insulation, lay them with the Kraft paper facing downward. Vapor would become trapped in the insulation if they face upward making it less effective and possibly allowing mold to grow on the floor joists.

        8. If you are laying batts or rolls over existing insulation, use un-faced batts or rolls or remove the Kraft paper. If the existing insulation is batts or rolls, and it was incorrectly laid with the Kraft paper facing upward, turn it over.

        9. If there are floorboards and you are adding a layer of insulation between the floor joists, remove the floorboards. If they are nailed down, pull the nails using a hammer and a “cat’s claw”.

        10. Whether laying batts or rolls or spreading loose fill insulation, leave 3” of space around the electrical boxes used for lighting fixtures and ceiling fans below. Also leave 3” of space around bathroom exhaust fans and non-IC recessed lights. These all create heat and release it into the attic.

          If covered with insulation, the heat is trapped, causing them to become very hot. The fixtures could be damaged or a fire could result. If you are laying batts or rolls, leave a space of 3” around each of these by cutting pieces from the insulation.

          If you are spreading loose fill insulation, make a small “fence” around each electrical box and lighting fixture using metal hardware cloth. IC recessed lights are designed to be in contact with insulation, but non-IC recessed lights are not. Recessed lights have labels inside, behind the bulb, which indicate which type they are.

        11. If you are using loose fill insulation, fill the spaces to slightly above the top edges of the joists. Sooner or later it will settle to the top of the joists. You could spread it by hand, using a large push broom or you could spread it rapidly using a rented insulation blower, and smooth it out with a large push broom. Do not use a rake because this could snag a low voltage wire or an electric cable.

        12. Keep the insulation 3” away from metal chimneys and gas water heater flues or other flues. Make a fence from hardware cloth if using loose fill insulation.

        13. If you are adding a layer of insulation above the floor joists and there is no flooring, cover the wires that pass over the floor joists to protect them. They will be buried but you could step on one and break it. Nail two small, thin pieces of wood onto the top surface of the joist, on either side of the cable. Nail a small, thin piece of wood over the cable and the two pieces of wood, as a ”bridge”.

          If you are laying batts or rolls above the floor joists, lay each one directly on top of a batt or roll, so you don’t cover the joists or truss members. These should stay visible so you can step on them.

        14. Avoid covering the soffit vents (see below)

How to Avoid Covering the Soffit Vents with Insulation

Whether you are using loose fill insulation or fiberglass batts or rolls, you must prevent the insulation from covering the soffit vents. Air must be allowed to escape from the attic through the soffit vents to prevent water vapor from being trapped in the attic. In addition, they allow hot air to escape in summer, lowering the temperature of the house or the demand for air conditioning. If the attic has a roof vent, gable vent or ridge vent, wind draws air out through this vent and in through the soffit vents to cool the attic on hot days.

        1. Soffit vents may be in the attic floor, where you can see them from the attic, or they may be in the eaves, where you can only see them from outside. These are called, “under eave soffit vents”. They are in the soffit overhangs (the eaves). Soffit vents in the attic floor may be small and round or long and thin. Soffit vents in the eaves may be round, rectangular or continuous.
        2. If you are laying batts of fiberglass insulation and you can see the soffit vents, lay insulation to the edge of the floor where ever there are no soffit vents. If you are laying the insulation on a floor where you don’t see soffit vents, leave a large space all along the wall.
        3. If you are laying loose fill insulation, you could prevent covering the soffit vents with insulation by mounting pieces of wood between the floor joists at each soffit vent to block the insulation. If the floor joists are 2″ by 10″ (nominal dimensions), as they normally are, the pieces of wood should be cut from 1″x 10″ (nominal) boards .
        4. If you are laying loose fill insulation and the attic is un-insulated, you could mount “rafter vents” (attic baffles). They are inexpensive and require very little work. They have channels that allow air to flow down between them and the roof and escape through the soffit vents. You must buy those that curve down to the floor to allow space for the soffit vents.

          Mount one rafter vent to the roof above each soffit vent. Insert them between rafters; they shouldn’t need to be stapled on, but can be if necessary.

          If the soffit vents are not visible, i.e., they are under eave soffit vents, mount rafter vents all along the attic floor. 

Seal the Air Leaks In the Attic Floor

The most effective way to lower your heating and air conditioning bills without spending much money may be to seal the openings in your attic floor. There are often, openings around light fixtures, for example. Sealing these openings will stop air from flowing up into your attic in the heating season and stop air from flowing down from the attic in the cooling season.

When a furnace or heat pump heats the air it expands and becomes lighter and, light a hot air balloon it rises to the attic through openings in the attic floor. It escapes from the house through the attic vents. Heated air and also cooled air is also drawn to the attic and out of the house by strong winds blowing over the roof. This is due to the “Bernoulli Effect”. Wind blowing over the roof lowers the air pressure, which draws air out of the attic.

When using air conditioning, the air in the attic is much hotter than in the rest of the house. If there are openings in the ceiling, the hot air in the attic will leak down into the rooms below due to the force of convection. Convection works in a cycle; warmer air flows toward cooler air and cooler air flows to replace it. Thus, air conditioned air will flow into the attic. Check for gaps to seal in these places:

      • From the floor below the attic, pull down the covers of the bathroom exhaust fans and check for gaps around the metal boxes. If there are narrow gaps, caulk them, but if they are too wide for caulk, seal them with commercial grade duct tape or aluminum duct tape (metal foil).

      • From the floor below the attic, check the recessed lights. Check for thin gaps between the trims and the ceiling. There will be gaps if the ceiling is not perfectly flat. Seal any gaps with clear caulk.

      • If there are registers on the ceiling, check that they tightly contact the ceiling. If there are gaps between them and the ceiling air will leak through the gaps. These registers may need to be attached more tightly to the ducts above, for example, a screw may be missing or loose.

      • If you have recessed lights on the top floor with cans (housings) and screw-in bulbs, check if they have IC (in contact) housings. These block air from flowing up into the attic because they have no holes in their housings, and are designed to be in contact with attic insulation. Non-IC housing recessed lights are not designed to be in contact with attic insulation. The insulation can cause incandescent bulbs to overheat and burn out. Determine which type of fixtures you have by looking at them from the attic. Turn the recessed lights on and turn off the attic lights. If light shines through them they are non-IC. The type can also be determined from below by reading their labels with their bulbs removed.

        If you have a recessed light with a non-IC housing, you can make it air-tight by replacing its bulb and trim with an “LED recessed lighting kit”. These are also called, “LED recessed light retrofit” and “LED recessed can light trim ring”.

        In a conventional recessed lighting fixture, the trim is held in place by springs, or by wires that you bend inward to mount the trim. The trim in some fixtures are not mounted that way but there will be 4 slots in the can for this type of trim. An LED recessed lighting kit has the same wires, and it is mounted in the same way. The electrical connection is simply screwing it into the socket for the bulb you removed. 

      • Check the ceiling lights and ceiling fans on the top floor of your home. Most flush mounted ceiling lights and almost all chandeliers and ceiling fans have a “canopy” that contacts the ceiling. If the ceiling isn’t flat or if the canopy is loose there will be a gap above the canopy. Air will flow up through the gap into the attic when the furnace is running, due to the “chimney effect”.

        A canopy is held against the ceiling by a retainer nut, and if this nut is loose the canopy will slip down slightly, so tighten any that are loose. If a flush mounted ceiling light without a canopy has a gap, remove the glass globe or shade and tighten the screws that mount the fixture to the electrical box.

        If tightening the retainer nut or the screws doesn’t close the gap, caulk the gap with clear, paintable caulk.

      • If you have a fluorescent light fixture that is long and thin or large and square, it may be mounted to the ceiling with two large toggle bolts which anchor it to the drywall or plaster. If a fixture is supported by toggle bolts, the bolts can loosen, allowing a gap between the fixture and the ceiling. Air passing through this gap will leak into the attic through the hole in the ceiling that the cable passes through.

        Remove the cover and check if there are toggle bolts and tighten them if they are loose. Then, check for a gap above the fixture caused by the ceiling not being flat. If there is a gap, caulk it with paintable caulk.
      • Seal the holes in the top plates. These are the 2×4’s that form the tops of the interior walls below. Electric cables, phone lines and low voltage wiring enter the attic through ¾” or 1” holes in them. In the summer, hot attic air flows down through them and is replaced by cooler air flowing out of them in a convection cycle.

        Sealing all of the holes takes much work, but it will be worth the effort if you do it yourself, rather than hire someone, because it will lower the cost of heating and cooling your home. Do this only with very good attic lighting to prevent stepping on wires or cables. Hang a trouble light from a rafter if more light is needed. If the top plates are buried in insulation, use the locations of the interior walls to locate them. Fill the holes with minimal expanding foam.

      • If there is a central air conditioning or heating unit in the attic, check for gaps where its ducts pass through the attic floor. The gaps around these ducts may have been sealed with duct tape or metal foil (aluminum duct tape) and this came loose. If it is loose, remove all of the tape and replace it with metal foil. This is sold in home centers and hardware stores in the HVAC duct section. Clean all surfaces carefully before applying tape.

      • If a water heater chimney flue runs through the attic, seal the gap around it where it penetrates the attic floor. It can become very hot, so the gap must be sealed with high temperature duct tape or with metal foil. Metal foil is the aluminum tape used for HVAC ducts. It is sold in home centers and hardware stores.

      • Check if one or more stacks runs through the attic, either boxed in, a “chase way” or in the open. A stack is a 2” or 3” diameter pipe that runs from a bathroom or kitchen to the roof. If your bathrooms are far apart on the same floor, there should be two chase ways, but if your kitchen and bathrooms are on the same side of the house, you should have only one chase way.

        If a stack is in a chase way, there may be a large gap around the pipe where it passes through the floor, hidden behind the walls of the chase way. This should be sealed because it acts as a chimney, allowing air to rise up through the chase way.

        If a chase way wall is made from drywall or plaster, cut a 6”x6” hole in it, reach through and fill the gap with expanding foam sealant. A hole of this size can be repaired with an 8”x8” drywall patch, which is sold in paint departments. You could ask a painter to patch the hole or you could do it yourself by watching a DIY video.

        If the chase way wall is made from boards, remove a board at the bottom or cut a large hole in it with a jig saw. The hole can be repaired by gluing in the piece that was removed, using construction adhesive. This type of adhesive will fill the gap made by the jigsaw because it is thick. If a stack runs through the attic and is not in a chase way, check for gaps around it at the attic floor. Caulk them if they are small or use expanding foam sealant if they are large.

        Block the gap between the chimney and the attic floor if . you have a brick chimney. This is typically 4” wide and may be filled with non-flammable insulation, but air passes through the insulation. Sheet metal flashing can be used to safely block the gap. Nail it to the floor and glue it to the bricks with roofing cement. Check that there is nothing flammable within 4” of the chimney, such boxes or wooden floorboards.

      • Check the insulation for dark spots. These are spots where air is leaking up from the living space below and the insulation is filtering out dirt. The most common location is above an interior wall that has cables running up through its top plate into the attic. Find the sources of the dark spots and seal these leaks.

      • If a whole house fan is mounted in the attic floor and you use it, check if the fins close tightly. These fans have fins that close against each other when the fan is not running, and air will leak between them if the fins don’t close tightly. If they don’t close tightly, clean them or try to straighten them. If your climate is cold, cover the fan with batts of fiberglass insulation in the heating season. Use faced insulation with the Kraft paper facing downward.

      • If a whole house fan is mounted in the attic floor and you never use it, cover it with plastic sheeting and fiberglass batt insulation. Staple the sheeting to the framing that supports the fan and screw down 1”x2” or larger boards over the staples to hold the plastic tightly to the floor. Lay fiberglass batt insulation over it if you have a scrap piece you can use. If not, buy a small roll of 2” thick fiberglass insulation which is used to insulated water heaters.

      • There is no ceiling above the kitchen cabinets in some homes. If there is no ceiling above your cabinets and they are a few inches from the ceiling with the gap hidden by wooden trim, there is a path for air to enter your attic. Air can flow up the exterior wall, behind the cabinets and into the attic. Block this airflow path from attic by inserting boards between the wall studs behind the cabinets.

Insulate the Knee Walls

Finished attics have short “knee walls”, which are between 2 ft. and 4 ft. high. The air behind them can be very cold, especially if the house has a ridge vent or a roof vent, because the wind in winter draws in cold air through the soffit vents and out through the ridge vent or roof vent. Roof vents run all along the ridge, and roof vents are circulars vents near the top of the roof.

Knee walls normally have small doorways that allow homeowners to crawl through. The door is made from a panel of thin wood or a piece of drywall, with framing around it. 

      • If a knee wall has no doorway, make one.  Having access to the space behind the knee wall will allow you to mount insulation to the back of the knee wall, to the floor behind the knee wall, to seal the holes in the floor where cables come through, and to use the space for storage.

        The simplest way to make a doorway is to cut a 14½” wide, 24″ high hole in the drywall between two wall studs and remove a piece of drywall. Replace the drywall with a thin piece of plywood. Use screws to remount it each time it is opened.

        If you prefer making a larger door with hinges to give easier access for storage, there are many DIY videos to show you how. Here are instructions for making it the simplest way, to insulate the space behind the knee wall.


        • Wallboard saw
        • Level
        • Hand saw or rotary saw
        • Large framing square
        • Construction Adhesive
        • ½” Plywood or thin hardboard. 
        • Trim molding for the frame such as “door and window casing” or a thinner type. 
        • White interior caulk
        • 1 ¼” Finish nails


        1. Warning – avoid cutting cables or wires behind the wall. To prevent this, start by knocking out a small hole with a hammer and reaching through to feel for cables and wires.

        2. Use a wallboard saw to cut a large hole to look at the wall studs from behind the wall. Check if cables are stapled to the wall studs to avoid cutting them.
        3. Mark the edges of the wall studs on the doorway side. If the wall studs are spaced at 16″, the two marks will be 14 ½” apart. Using a level, draw a line from top to bottom on each wall stud. These will be the cutting lines. If a long level isn’t available, hold a 6″ level on a long, straight board and trace along the board.
        4. Using a level, draw the horizontal cutting lines for the top and bottom of the doorway.

        5. Cut out the opening with the wallboard saw.
        6. Cut a piece of wood slightly smaller than 14 ½” x 24”, from hardboard or ½”plywood to fit into the opening. Do not use ¼” plywood because this is more likely to warp. Use a large framing square to draw the cutting lines on the wood.
        7. Cut 4 pieces of trim molding, such as window casing, to nail onto it as a frame. TIP – Buy more than necessary, to re-cut pieces that were cut poorly. Window casing is at least 2 ¼” wide, so you may prefer a thinner type of trim molding.

        8. Apply construction adhesive, then nail the trim molding to the piece of wood with 1 ¼” finish nails. Caulk where pieces meet with white interior caulk. Paint when the caulking is dry.

        9. Mount the door using Velcro or 4 screws. If using screws, drill pilot holes to prevent cracking the wood.  


        1. Hang a trouble light to prevent stepping on a wire or cable.
        2. Measure the spacing of the wall studs; they will be spaced at 16″ or 24″. 
        3. Measure the total area of the knee wall.
        4. Buy “unfaced” 15″ wide or 23″ wide 3½” thick fiberglass batts or rolls. This has no Kraft paper. If only faced insulation is available, buy this and tear off the Kraft paper (see below).
        5. Buy a box of 100 16″ or 24″ “insulation supports”. These are stiff wires used to mount fiberglass batt or roll insulation between wall studs or rafters.
        6. Cut the insulation into pieces the height of the knee wall, and stuff in a piece between each two wall studs. Fix them into place by pushing in insulation supports. Put one in at the top, middle and bottom of each piece of insulation.

The insulation must not have Kraft paper because air may flow through the insulation in different directions in different seasons. Kraft paper on either side would trap water vapor in the insulation when air is flowing from the other side. In winter, the air will flow outward from the finished area of the attic and in the summer the air may flow inward.

      • Block the spaces under the knee wall between the floor joists. In the heating season, air that leaks up through the attic floor at lighting and ceiling fan fixtures flows under the knee walls where it escapes through the attic vents. It flows out forcefully due to the chimney effect. If the floor is built from engineered floor joists, it may not be worth your effort to block the spaces. To block the spaces:


        1. Measure the width of the floor joists. Buy boards of that nominal width, with nominal thickness of 1″. For example, if the floor joists have nominal dimensions of 2″x 10″, buy boards of nominal dimension 1″x 10″. Both will be about 9½” wide.

        2. Cut the 1″ thick boards into lengths to fit between the floor joists. They can probably all be cut to the same length.
        3. Glue in the pieces with general purpose construction adhesive. This seals the gaps so caulking shouldn’t be necessary. 

      • Do not fill the spaces above the knee walls. On hot days, these spaces are pathways for hot air above the attic’s ceiling to flow down to the soffit vents and escape. If there is a ridge vent at the top of the roof or a roof vent near the top of the roof, these spaces allow air to flow into the attic through the soffit vents and up to the vent to ventilate the attic in all seasons.

Insulate the Attic Walls


      • Whether your attic is finished or unfinished, check if the gables are insulated. A gable is a triangular attic wall. The gables may be un-insulated if your home is very old. You can check by touching them on a cold day, if they feel cold they are un-insulated.

        Gables can be insulated with loose fill insulation, Perlite insulation, or fiberglass batt insulation. Expanding foam sealant is no longer recommended for insulating walls because it may allow the growth of mold.

      • If the inner surfaces of the gables are made of boards and there is no insulation, try to remove the boards and put in fiberglass batt insulation with the Kraft paper facing inward. In most areas of the country, these walls will be 3½” deep, but if your climate is cold they may be 5½” deep. You could use 3½” thick fiberglass batt insulation for either wall thickness.

        This may be the best thickness for 5½” thick walls because it allows 2” of space next to the exterior surface. This “dead air insulation” prevents heat from being conducted into the house in the summer and conducted out of the house in the winter.

      • If the inner surfaces of the gables are made of boards and the boards are very hard to remove, try to remove the top board and either pour in Perlite insulation or blow in loose fill cellulose insulation. Perlite is made of small balls of insulation and is designed to pour into walls. It is available at some builders supplies but not at home centers. It has a lower R-value than loose fill cellulose insulation.

        To blow in loose fill cellulose insulation, rent an insulation blower at a hardware store, home center or rental store. They are rented at many places where loose fill cellulose insulation is sold. They give instructions there on how to use the blower.

      • If the gables are unfinished, insulate them with fiberglass batt insulation as explained above.

      • If the inner surfaces are covered by drywall, fill the wall with loose fill cellulose insulation. Rent an insulation blower at a hardware store, home center or rental store, at many places where loose fill cellulose insulation is sold. The store renting the blower should have someone to give instructions on how to use it.

        This is basically what you will do: 1) Drill a 2” hole every 16”, between the wall studs, at the top of the wall and blow it in; 2) Stick the hose into each hole and blow in the insulation; 3)Repair the holes with 4” wall patches. You can buy them at a paint store, where you can ask how to use them and they can sell you the plastering tools you will need.

      • If your attic is finished, check if the small areas of the gables that are behind the knee walls are insulated. Use 3½” thick fiberglass batt insulation to insulate them, with the Kraft paper facing inward, whether the wall is 3½” deep or 5½” deep.

      • In the heating season, warm air can escape from the house by flowing under the knee walls between the floor joists, and out through the attic vents. There is normally fiberglass insulation under the knee walls, but air flows through this, drawn through forcefully by the “chimney effect” when the central heating is on. Wooden blocks could be inserted between the joists, below the knee wall, to block this flow of air.

        If you put in wooden blocks, glue them in with construction adhesive. This is as thick as caulk, so it seals gaps. Tightly-packed cellulose insulation may also be used, which can be stuffed in by hand. Spray foam insulation is not recommended because it can allow mold to grow.

      • If walls separate your attic from your living space, as they do in split level homes, check if they are insulated. If you touch a wall from the living space side on a very hot day it will feel hot if there is no insulation. To insulate these walls:

      • If your air conditioning costs are high but not your heating costs, you could insulate these walls for the cooling season by only covering the attic side with radiant barrier insulation. This reflects heat radiation (UV radiation). It takes very little work to mount; staple the barrier material to the wall as you unroll it. It is described above in Radiant Barrier Insulation.

      • If there is a skylight above the attic with walls around it to direct its light to the floor below the attic, the walls may be made of a single layer of drywall mounted to wall studs. Insulate these walls using 3½” fiberglass batt insulation with the Kraft paper facing the attic.

        If your home is very old, these walls may be made from 4” wide tongue and groove boards without wall studs. This could be insulated by stapling on 3½” fiberglass wall insulation with the Kraft paper facing the attic. Some types of rigid board insulation could also be used to insulate tongue and groove boards but most types can only be used when covered by drywall because they release toxic fumes in a fire.

Other Places In the Attic to Insulate

      • If a stairway leads to your attic and you live in a very cold climate, fill the space under the stair treads with insulation and insulate the stairway wall. To fill the spaces under the stair treads, pry off the top step tread and pour in loose-fill cellulose insulation. It will slide down and fill the space under all of the stairs.

        This insulation is available at home centers. The stairway walls could be insulated with 3½” fiberglass batts if the wall studs are exposed. On very old homes, the inner wall surfaces may be built of 1′ thick boards. Remove the top board and pour in loose fill cellulose insulation.

      • If the entrance to your attic is a hatchway, weather strip it to make it air-tight. A gap here may greatly raise you heating costs. There is often a large gap where the hatch rests on the frame, either because the frame was poorly built or because the hatch is built from thin plywood and it has warped.

        If your hatch is built from thin plywood and has warped, straighten and strengthen it by screwing 1” thick boards to the back of it. Cover the top of the hatch with insulation if you live in a cold climate. Buy a roll of 1” or 2” thick fiberglass insulation that is used for water heaters and cover the hatch with several layers of it.

        Seal the gaps between the hatch and frame by laying ¼” thick foam self adhesive weather strip onto the top surface of the frame and stapling it to last longer. This type of weather strip will compress to a paper-thin thickness to seal a gap that varies in thickness around the edge of the hatch.

      • If a stairwell leads directly from the basement to the second floor, there may be a large path for air to flow from the basement to the attic, between the wall studs in the stairway walls. Locate the top of the stringers in the attic. One is on each side of the top of the stairway. These are 2″x 12″ boards that support the stair treads. If there is a gap in the floor next to a stringer, seal the gap with expanding foam sealant.

      • In split level homes, there is often a serious source of air leakage into the attic. In the stairwell leading to the second floor, the warm air in the stairwell walls may rise unobstructed from in the second floor walls to the attic. In the attic, locate the top of the stairwell wall studs. If there are open spaces between them, fill these spaces with expanding foam sealant.

      • If your attic has dormers, check if their walls and ceilings are insulated. If un-insulated, they will feel cold on a cold day and hot on a hot day.

        If the walls are drywall or hardboard, remove it. Hardboard can be removed and re-used because it was nailed on. If so, try to pull the nails with a cat’s claw. Put in 3½” fiberglass roll or batt insulation with Kraft paper removed, and replace the wall.

        The Kraft paper must be removed because it must face the warmer side of the wall, or else water vapor will be trapped in the wall. On hot summer days, if the house is air conditioned it could be hotter outdoors, and in winter it is always hotter in the attic.

        If the inner surfaces are built from 1” thick boards, you could remove the top board and pour in perlite insulation if it is available. It is available at some builders supplies. You may be able to use loose fill cellulose insulation. For this, remove a board near the middle of the wall and stuff the insulation upward and downward to fill the space, using a long, flexible brush such as a toilet bowl cleaner. Spray foam insulation is no longer recommended because it can result in the growth of mold.

Cover Recessed Lights and Other Electrical Fixtures with Air-Tight Covers

There are several ways to cover non-IC recessed lights, bathroom exhaust fans, and electrical boxes for ceiling lights to make them airtight. Building boxes from plywood is not included because they may eventually warp and not remain airtight. Non-IC recessed lights are described above in Seal the Air Leaks in the Attic Floor. There are three types of airtight covers:

Spun Stone Recessed Light Cover
Spun Stone Recessed Light Cover

    1. Spun stone recessed light covers. These are made from a fire retardant material. They are easily bent to fit irregular spaces. They are sold at some home centers and can be ordered through a home center. They require the least work to mount and the material is easily cut with a wallboard knife.

      They should not be used if you have new construction recessed lights because four slots would have to be cut in them for the support bars and the slots would be very hard to make air-tight.

    2. Box in the recessed lights or other electric fixtures between floor joists or rafters. If you have joists, you can box in recessed lights by cutting two pieces of 1” thick wood of the width of the joists and nailing them in crosswise between the joists on either side of the fixture. You cover the top with plywood or other electric fixtures See How to Box In Electric Fixtures Between Floor Foists or Trusses.

    3. Five gallon plastic buckets. These are inexpensive to buy and you may already have some. They are the containers used for paint, joint compound and cleaning products. They are sold for about $5 at home centers, hardware stores and paint stores. When working in the attic, always wear a respiratory mask and be sure that the attic is well lit to prevent stepping on wires or electric cables.

How to a Mount Spun Stone Recessed Light Covers


        • Wallboard knife
        • General purpose construction adhesive
        • High grade caulk
        • Duct tape (to hold down light cover while adhesive dries)


        1. Cut notches for the electric cables using a wallboard knife. Cut them for the cables to fit in tightly because gaps around the cables must be filled with caulk.
        2. Carefully clean the surface of the floor where the light cover will lay.
        3. Trace where it will lay and apply a thick bead of construction adhesive. Set the light cover into the bead and tape it down with duct tape to hold it while the adhesive dries.
        4. Apply caulk around the cable

How to Box In Recessed Lights and Other Electric Fixtures Between Floor Joists or Trusses


If the attic floor joists are standard 2” by 10”, you can probably box in the recessed lights and other fixtures between the joists between two 1”x10” boards, with a plywood cover. As explained above, only non-IC recessed lights allow air to pass through, and these can easily be replaced by an “LED recessed lighting kit” to make them air-tight. If your attic is built from trusses, the floor is probably built from 2”x 6” truss members. You can box in recessed light fixtures by building boxes with four 1”x10” walls and nailing one wall to a truss member. The other electric fixtures, such as flush mounted ceiling lights, can be boxed in with two 1”x6” boards that extend from one truss to the other. After boxing in a recessed light or other fixture, cover it with ¾” plywood.

If the Attic Floor Has 2″x 10″ Floor Joists:


        • 1”x 10” or 2”x 10” boards
        • ¾” plywood to cover the tops of boxes
        • 2” drywall screws
        • One tube of caulk for each 4 fixtures. “Window, door and siding sealant” is more durable than interior/exterior caulk. Sealant is caulking, but more elastic than most types of caulk.
          general purpose construction adhesive


        • Tape measure, combination square or small framing square (to check if joists are vertical)
        • Miter saw, table saw or rotating electric saw
        • Hand saw (to cut notches)
        • Pliers (to break out the notches)
        • Cordless drill
        • Clamp-on trouble light
        • Respiratory mask
        • Wisk broom or paint brush (to clear surface of attic floor)
        • Caulking gun
        • 5/16” drill bit


        1. Remove any objects from your pockets. They could fall out while lying on the attic floor and be buried in the insulation.

        2. Put on a respiratory mask and hang a clamp-on trouble light.

        3. Check that the board you will cut for the side pieces is exactly the same width as the joists. If it is wider, trim it with a rotary saw.

        4. At each location, measure the distance between the joists. Check if any are leaning to one side from being slightly warped. If any are leaning, measure the distances between the joists at the top and bottom, to cut each board to fit. Cut two pieces of that length from a 1”x 10” or 2”x 10” board.

          If you measure at all the locations before you begin cutting, you will probably find that all the pieces should be cut same length and all at right angles, so you can save time by cutting them all at once.

        5. Allowing 3” of space on each side of each fixture, measure and cut pieces of ¾” plywood to mount on the top of each. If a board must be closer than 3” due to an obstruction, allow more than 3” for the other board.

        6. At each fixture, use a hand saw to cut notches for the electric cables. Make two cuts and break out the piece with the pliers. Make the notches a tight fit so that the gap can be filled with caulk.

        7. Carefully clean off the surface of the floor where the side pieces will be mounted and glue them down using construction adhesive. The adhesive must be thick to seal any gaps.

        8. Screw the side pieces to the joists. First, drill 5/16” holes into the edges of the side pieces at 45° angles, to lead the screws into the joists.

        9. Caulk the interior corners with heavy beads of caulk and press it into the cracks.

        10. Lay a bead of caulk along the top edges of the two boards and the joists and set the the top piece down onto it. Drill 5/16” holes around the perimeter of the top piece for screws and screw it down using 2” drywall screws. The holes prevent the wood from cracking and create a tighter seal. Use many screws to prevent the wood from warping in the humid attic.

        11. Seal around the electric cable with caulk.

If the Attic Has Trusses with 2”x6” Bottom Members:

If your roof is built from trusses, then the floor will normally be made of 2”x 6” truss bottom members spaced 24” apart. The fixtures that are not recessed lights will be less than 6” high, so they can be boxed in using 1”x 6” boards. These fixtures include ceiling fans, bathroom exhaust fans and flush mounted ceiling lights. Use the tools and instructions above, except use a 1”x 6” board in place of a 1”x 10” board. Recessed lights are higher than 6” so you must build a box around them with 1”x 10” sides and screw it to a truss.



        1. If 1”x 10” boards are used, cut four pieces for walls of a box, allowing 3” between the fixture and the walls of the box.

        2. If the fixture is too close to the truss to put in a four-sided box, make a three-sided box and leave more than 3” on the side opposite to the missing piece to compensate. Screw the pieces together and mount the box to the truss. Cut a piece 4” wide to mount on top of the truss to fill the space.

        3. If 1”x 6” boards are used, cut three pieces to make a three-sided box and screw it to a truss.

        4. Follow the instructions and use the tools and materials given above in If the Attic Floor has 2”x10” Floor Joists

How to Mount a 5 Gallon Plastic Bucket


        • Hand saw
        • Metal shears or sharp wallboard saw to cut notches in bucket
        • Polyurethane construction adhesive
        • Caulking gun
        • Scrub brush
        • Minimal expanding spray foam to seal around cables
        • One brick or other heavy weight for each bucket to hold it while adhesive dries


        1. Cut notches in the bucket for the cables using metal shears or wallboard saw. Make each notch a close fit so that the gaps around the cables can be well sealed.

        2. Use a scrub brush to thoroughly clean the area on the floor where the bucket will lie to prepare it for gluing.

        3. Lay the bucket on the attic floor and trace around its perimeter. With a caulking gun, lay a large bead of polyurethane adhesive along the circle to lay the bucket into. Lay the bucket into the adhesive and put a weight on it.

        4. Seal around the cables using minimum expanding spray foam.


I hope you will do many of the things described in “DIY Attic Insulation”, and if you do, Be Careful!