Best Practices for Basement Insulation

Best Practices for Basement Insulation


Installing basement insulation is different than insulating other places in the house because of the likelihood of mold forming.  Strangely enough, concrete acts like a sponge since it is extremely porous.  Due to its porous nature, you use foam board to insulate instead of fiberglass.

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Make Sure Everything Stays Dry:

The first thing you want to do when installing basement insulation is to make sure your foundation is sealed.  One way to test is to tape a plastic sheet to the cement wall and let that sit for a week.  If no condensation forms between the plastic and the concrete, your basement is sealed.  However, if condensation does form, you will need to seal and waterproof your basement.

There are various ways to seal your foundation.  Typically, what you want to do is use a hydraulic cement to fill any cracks or holes in the foundation.  Look for rust marks on the walls.  Often, they are indicative of where there may be a crack or leak.  If you are still having issues with moisture, it may be necessary to use a product that is like a paint and paint that product on the concrete walls.  A sales associate at a hardware or home improvement store should be able to guide you to these products.  Once you are confident there is no moisture coming in, you can begin to insulate your basement.


If there is a stud wall:

Make sure your rim joist is insulated.  Start by sealing the rim joist above the stud wall.  Use 2-inch foil faced polyiso to insulate the rim joist.  Seal the edges of the insulation and the utilities with spray foam.

Now, to insulate the stud wall, what you need is a vapor barrier.  Luckily, you can use the same insulation board you use to insulate any concrete wall as a vapor barrier.  For the foam board to act as a vapor barrier, it must be, at minimum, 1 ½ inches thick.  You can screw it in place into the stud wall.  Your stud wall should now be insulated.


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To insulate a concrete wall in the basement:

You can apply your foam board directly to the concrete.  Use an adhesive made specifically for foam board.  Always avoid use adhesive with a solvent because adhesives with a solvent deteriorate foam insulation.


After you’ve attached your foam board to your basement walls, you have insulated your basement.  Typically, the process goes quickly and it is not as daunting as it may sound once you start.  Remember, avoid fiberglass for basement insulation as much as possible.  Aside from that, you should be good to go.