How to Insulate Basement Walls

Three Methods:Choosing a Type of InsulationInstalling a Hybrid Insulation of Rigid Foam and FiberglassInstalling Spray Foam Insulation

Homes in colder climates lose a tremendous amount of heat through basement walls. An energy-efficient basement can help to prevent much of this loss, while saving you money on energy bills. If you know how to insulate basement walls, you can easily make your basement energy efficient, by keeping it both warmer and drier than a non-insulated basement.

Method 1
Choosing a Type of Insulation

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    Choose an R-value. R-value is a measure of how well an insulation does its job of reducing hot or cold airflow. A higher R-value, per inch of thickness, indicates better insulation. The R-value you will need depends on the climate where your home is located and on how well insulated you’d like your home to be.
    • For example, if you live in a warm climate, you would want a minimum value of R-30.
    • Cold climates would require a minimum value closer to R-60.[1]
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    Evaluate your insulation options. R-value will help you choose the level of insulation that you’ll need. There are many basement insulation types. Three of the most popular types of insulation are batt-and-roll (blanket), loose-fill, and sprayed-foam.
    • For blanket or batt-and-roll insulation, simply nail or staple the insulation into your wood frame. Blanket insulation is usually available in standard wall-frame sizes.
    • For loose-fill insulation, install drywall over the studs before adding the loose-fill insulation.
    • Sprayed-foam insulation is the most energy-efficient option for insulating a basement. It may be necessary to rent equipment to insulate your basement with wet-sprayed cellulose. This equipment is available at most major hardware stores. Sprayed foam can be open-cell or closed-cell.
      • Open cell simply means there is air between the many bubbles made by the sprayed foam.
      • Closed-cell, though slightly more expensive, is filled with non-air chemicals that are more efficient at insulation.[2]
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    Consider additional treatments for your insulation. Additional treatments can help protect against moisture and can be more fire retardant.
    • Faced insulation uses vapor barriers that control moisture movement between walls.
    • Unfaced insulation does not have vapor barriers, but you might not need a vapor barrier if, for example, you’re applying over existing installation or if moisture control is unnecessary.[3]
    • Fire-rated coverings are often necessary, since many types of insulation release toxic gases when ignited. Consult your local building code to see if this is necessary.[4]

Method 2
Installing a Hybrid Insulation of Rigid Foam and Fiberglass

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    Frame the wall with wood. (If you plan on installing a vapor barrier, consult that section now, as certain vapor barriers go between the wooden frame and the concrete wall.) Consider using composite decking on the floor of the basement for extra moisture protection, or you could use a pressure-treated 2x4 bottom board.[5] Otherwise, use standard wall-framing techniques to build the wall studs. Use a level to plumb the framed wall, and leave about a one-inch gap between the stud wall and your cinder blocks to provide plenty of space for insulation.[6]
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    Choose an insulation board. Boards can include molded expanded polystyrene (MEPS), extruded expanded polystyrene (XEPS), or urethanes such as polyurethane. For a basement wall, XEPS is usually recommended since it’s firmer and has a higher R-value than MEPS, which is the least expensive option but not as strong. The urethanes, another option, are solid and often used with plywood.[7] A minimum of 1.5 inches of board thickness is usually recommended.[8]
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    Cut the board and position it in place. Cut the board to fit between the studs from side to side and against the concrete wall.[9] Use constructive adhesive to attach the board to the wall and use caulk or expanding foam around the edges of the board and against the studs.[10] Remember to install from the bottom all the way up to the top of the wall.
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    Seal the board's seams. This is an important part of securing the vapor barrier. Examples of sealants include tapes, such as Tyvek Tape and Dow Construction Tape or canned foam like Great Stuff.[11] Cover the seams or cracks between the boards and between the boards and studs or concrete.
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    Install fiberglass. The fiberglass will be placed in the wall cavities created between your frame and the foam insulation board. Nail or staple the rolls or sheets to the wooden frame. A nail gun can be an efficient way of nailing in the rolls or sheets. Remember to take safety precautions here, and to wear protective goggles and gloves.
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    Add a vapor barrier. This is an optional step, but some people like to add a vapor barrier between the fiberglass and the drywall. This is particularly recommended if the foam insulation board you initially installed is less than 1.5 inches thick. Concrete or block walls absorb moisture like a sponge, and will periodically release moisture toward your drywall, studs, and joists.[12] The vapor barrier helps prevent moisture from causing mold to develop in your insulation, which can be very expensive to fix.
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    Cover the insulation with a wall surface. Whether you use batt-and-roll insulation, loose-fill insulation, or sprayed-foam insulation, you do not want to leave the insulation exposed. You have many options for wall surfaces. Drywall is commonly used to cover the basement insulation, but if aesthetics are not a concern, you can also cover the insulation with plywood.
    • Cover your insulation with drywall. Drywall usually comes in 4’x8’ sheets that you will need to measure and cut to fit your walls. When hanging drywall, start at a corner. Prepare the studs, joists, or strapping by applying glue to the surface immediately before you plan to hang the drywall. Then, use screws or a nail gun to nail the drywall. After all the drywall is hung, mix your mud and apply it with a putty knife along the seams between the drywall panels and in the corners. Cover these areas with drywall tape as well. After the mud dries, sand down and smooth over each mudded area.
    • Alternatively, use plywood over your insulation. Plywood might require bending to cover up all of your insulation. This might involve laminating multiple pieces of plywood; steaming or soaking the plywood; or cutting kerfs (i.e. grooves) and reinforcing them with wood glue. Also, try to find plywood without knots, particularly in areas that are to be bent.

Method 3
Installing Spray Foam Insulation

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    Choose your preferred spray foam insulation. Spray foam insulation is more expensive than foam board and fiberglass insulation, but it can be preferable since it yields a higher R-value. Remember, you can use either open-cell, closed-cell, or a combination.
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    Use safety equipment. At a minimum, you should wear a disposable coverall suit with hand and foot coverings as well as a respirator. (While a simple mask might work for fiberglass installation, you’ll need a respirator when dealing with foam.) You’ll also want a hood and goggles that fit securely around your eyes and temples.[13]
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    Leave space between the frame and the wall. Make sure your frame is set off of the wall about 4 inches. This will allow you to spray a continuous foam barrier behind the 2x4s that is uniform throughout the basement.[14] As the foam expands and as you continue to spray, you’ll want to examine the walls to ensure this uniformity.
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    Spray closed-cell foam. Spraying foam insulation is usually a job for professionals, but if you do it yourself, you will need closed-cell insulation’s two main ingredients, often called components A and B. Use a heated hose to send the components through a mixture gun (a chemical reaction will begin immediately upon mixture), and spray onto the surfaces that need to be insulated.[15]
    • Spray about 2 inches on walls. Consult your energy codes, if any, but 2 inches on walls and 3 inches on rooflines is customary.[16] Spot check in various areas to see ensure that the foam thickness is uniform throughout.
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    Remember to spray sparingly. Closed-cell foam will expand to about 25 times its liquid size and form a moisture barrier. Since it also has a higher R-value than open-cell foam, you’ll get more insulating power for a smaller amount.
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    Alternatively, use open-cell foam or a combination. If you plan on spraying with open-cell foam, which also expands considerably, you’ll want to insulate your band board and basement joists first.[17]
    • Here, you can save money by applying closed-cell foam just to the band boards and joists. Before spraying the open-cell foam, spray small amounts of closed-cell foam onto these areas. You’re just trying to seal up the cracks to reinforce the insulation. Then, spray the open-cell foam upon the insulation areas.
    • Alternatively, you could use caulk or Great Stuff, a polyurethane-based insulating foam, on the band boards and joists.[18] Again, you’re just trying to form a seal to prevent air and moisture from seeping through the cracks.
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    Spray open-cell foam. After your band boards and joints are insulated, you’re ready to spray. Apply open-cell foam in the same way that you apply closed-cell foam: with a heated hose and mixing gun. However, you’ll likely use a thicker layer of open-cell foam since open-cell’s R-value is lower.[19] Use about a 3 to 5.5-inch-thick layer of open-cell foam.[20] Fortunately, open-cell foam expands and fills framing cavities better than closed-cell foam. So, it will be easier to track your spraying progress.[21]


  • Check local codes to determine if you are required to add fire-rated protection over the insulation. Even if not required by code, adding fire-rated covering can add additional protection.
  • Because the basement is connected to the rest of your home, insulating the basement ceiling does not afford as much energy-efficiency as insulating the basement walls. Insulating the walls does more to protect your home from outside temperature and moisture. Insulating the walls is also easier and requires less insulation.
  • If you are building a new home, ask the contractor about concrete block insulation or insulated concrete forms, which can be installed during construction and provide additional energy efficiency in your basement.

Sources and Citations

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Categories: Interior Walls Ceilings and Floors