How To Insulate Basement Walls
Written by Todd Fratzel.
How To Insulate Basement Walls
Insulating a basement properly is rather challenging in cold climates. In this article I’d like to discuss how to insulate basement walls in cold climates.
Insulating basement walls in cold climates is a great way to keep your home warmer and drier. However, special care should be used when insulating concrete (or block masonry) basement walls. Below grade concrete foundation walls are very cool and damp. If you were to insulate the walls with regular fiberglass batt insulation it is very likely that a mold problem would develop.
Recommended Basement Insulation
Therefore I recommend using a combination of products to insulate basement walls. In order to create a vapor barrier and separation between the concrete walls and wood framing I like to use extruded polystyrene insulation (blue board from DOW).
Next we frame a traditional wood stud wall in front of the polystyrene insulation. We do take one special step in framing the wall. First we install a layer of composite decking between the concrete slab and the pressure treated bottom plate of the wall. Finally we install some type of insulation in the wall cavities.
Step 1 – Install Extrude Polystyrene Insulation Boards
The first step in insulating a basement wall is to install the polystyrene insulation (for more information we recommend reading: R Values Of Foam Board Insulation). We like to use a all purpose adhesive that’s approved for Styrofoam products. After the polystyrene insulation is installed each of the joints is taped with construction tape (there are several available from Dow, Tyvek, and other house wrap manufacturers) or some other approved tape that adheres to polystyrene insulation. By taping the joints you are helping keep moisture and cold air from infiltrating into the stud wall cavity.
I recommend you seal the top and bottom of the foam board using spray foam from a can. You can buy products like Great Stuff that will seal those joints very well. Be sure that you install foam board on top of the concrete wall up tight against the wall plate and seal that well.
Want to see how this is done? What the following short video:
Step 2 – Frame Basement Wall
Framing the basement walls is very straight forward. Use traditional wall framing techniques with two slight modifications. First I recommend installing a piece of composite decking (Trex, TimberTech, etc.) on the slab (use a Powder Actuated Tool to shoot the decking into the slab) below where the wall bottom plate will rest.
By installing a piece of composite decking (see arrow in photo) you will ensure that water does not “wick” up into the wall should there ever be any water leaks in the basement. Next just frame the wall with a pressure treated bottom plate and stand it up. Nail the top plate into the first floor joists and then nail the bottom plate into the composite decking. Be sure to plumb the wall with a builders level.
Step 3 – Insulate Stud Wall Cavity
Now you’re ready to insulate the stud wall cavity. There are a couple of options here as well. You can insulate the wall with fiberglass insulation, you can use wet sprayed cellulose insulation or you could use spray foam insulation. I insulated my basement walls with fiberglass insulation. For this house we’ll be using wet sprayed cellulose insulation. I’ll be sure to write several posts about the spray applied cellulose insulation when we get to that step of this project.
Rim Joist Insulation
Don’t forget to insulate your rim joists. Rim Joist Insulation is a very important component of the basement insulation process. There are several options including spray foam, foam board and fiberglass insulation. We recommend using rigid foam board insulation if you’re going the DIY route.
There have been tons of questions about whether or not to use a vapor barrier. The discussion is complicated so we wrote another article about the topic. Please check out: Vapor Barriers For Basement Insulation.
Step 4 – Finish Wall Surfaces
The final step is installing some type of finished basement wall surface. We’ll be installing normal drywall in this basement. You could certainly use most any material type that you want.
Short Basement Insulation Video
Many of the topics covered in this article are also discussed in a short video that I made. The basement insulation video highlights a basement with regular concrete walls and a walkout framed wall.
Basement Wall Insulation Summary
Insulating your basement walls will help keep your home warmer and drier. By insulating them properly and creating an effective vapor barrier you’ll be able to reduce the amount of moisture that enters into your basement from the damp moist concrete walls. Concrete is always full of moisture so it’s very important to keep materials like wood and fiberglass insulation away from the concrete surface. By taking the time to properly insulate your basement you’ll be able to enjoy the extra space for years to come with little maintenance.
Recommended Tools and Reading
I also suggest you check out the following insulation books: Insulate and Weatherize and The Homeowner’s Handbook to Energy Efficiency. If you’ve just recently moved into your home you may be able to take advantage of a Lowes Coupon for new home owners and save some money on your insulation supplies.
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