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Basement Insulation

We get a lot of inquiries about remodeling projects, and the majority of them are basements. The basement is an interesting space that is often overlooked. When shopping for a home, buyers put a lot of emphasis on the above-ground levels of the home, because that's the livable space that you will spend most of your time in, and, frankly, the part that impresses your family and friends! But the basement is often an afterthought. Why is that? Usually, its because the basement is utilitarian and unglamorous. But basements are super important: they are the guts of your home. And a good basement can improve your quality of life.

Having just gutted and remodeled my own basement, I could go on and on about basement remodeling. But for this update, I want to focus on just the insulation. Why is basement insulation important? In a nutshell, it's the difference between a humid and moldy basement and a dry and safe basement.

Remodeling Contractor

Drain tile before the concrete is poured.

There is a lot of information on the web about how to properly insulate your basement. I think this is because for a long time people were doing it incorrectly and it takes time for opinions to shift and a new consensus to be reached. What we do know is you can't treat a basement wall like you would an above-ground one; that is a recipe for disaster.

The following is what I recommend to customers. However, sometimes customers have done research for themselves and have come to a different conclusion. We are happy to insulate using a variety of current techniques and materials.

Step 1. Assess your situation. What do you need? If you've had issues with flooding or dampness on your basement floor, then I highly recommend installing drain tile. It is a relatively inexpensive insurance policy for your basement remodel. I never want to have to replace carpet and drywall in a newly-finished basement because of a heavy rain or broken downspout! Let the pros install drain tile, it's not terribly complicated, but is a ton of work jackhammring and hauling rock and debris.

Step 2. Spray foam your rim joists. This is the most effective way to insulate your rim joists. I don't recommend this step as a DIY project. Have the professionals take care of this one, as this typically requires a lot of foam (you'd go through 100 cans of the kind you might buy at the store). Keep in mind that while this job will be done in one day, you'll have to vacate the premises for 24 hours due to the chemicals in the foam.

St. Paul

Rim joists are insulated with spray foam

Step 3. Apply closed-cell foam boards to the wall. You may also elect to spray foam the walls, which is the most effective way to do it, but also far more costly. The boards must be a minimum of 2" in thickness to act as a proper vapor barrier.

If you're looking to save some money on your remodel, this is a great DIY step. The foam boards should be in stock at any construction store. They typically come in 8'x4' sheets. You can cut them to size using a box cutter (I use a metal ruler and/or chalk line to help get a clean line.) The boards should fit snugly up against your joists (or ceiling if you've got one up already). Apply construction-grade adhesive liberally to the back of the board and then push the board up for a minute or two. Make sure the adhesive you use is anti-fungal.

Minneapolis

Foam boards applied to a basement wall.

Step 4. Seal your foam boards. Another DIY step, it consists of using an anti-fungal spray foam in between the seams and along the top near the rim joists. Use a silicone caulk along the floor and walls where the foam stops. The overall goal here is to prevent any air from flowing behind the foam boards. This is key in preventing mold and heat loss. Then use a tuck tape along the seams for good measure.

After your foam boards (or spray foam) is applied to the block walls and properly sealed, it is time to frame. The framing may or may not come in direct contact with the foam, but it is very important to make sure not to puncture the foam with nails or screws. Other framing tips: 1. Use green-treated lumber for the base. The wall boards can be standard. 2. If you're framing directly above drain tile, make sure to use Tapcon concrete screws to secure your base.

Remodeling Contractor

Framing up in front of the foam.

Step 5 - Optional. Once your framing is done, you may elect to use bat insulation between the studs as you would for above-ground walls. If you've got a walk-out basement, this will increase your R value on the walls that are not below ground. It is unnecessary for the walls that are. Remember, you already have a vapor barrier in place so do not use plastic between the bat insulation and the drywall, or you will create a moisture zone that will breed mold!

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