Best Insulation Method for Basement Walls

Basements provide for a very tasking insulation challenge due to high moisture levels and cooler temperatures. However, you can achieve great results when basement insulation is done the right way.

In this article, you’ll find a summary of expert experiences (wins and fails) and learn some of the best basement wall insulation installation practices.

Best Insulation Method for Basement Walls

Basement wall framing for insulation


Understanding Basement Insulation Challenges

You probably have lost count of the number of incomplete basements you’ve seen with wood-framed walls directly against the concrete and the cavities of the framing filled with fiberglass insulation material in direct contact with the concrete foundation walls. This type of detail almost always leads to a serious mold problem and obviously a potentially hazardous health concern for the property dwellers.

Most people don’t comprehend the microscopic composition of concrete and often overlook the high moisture levels present in concrete. We often hear people say to us, “the concrete walls are extremely dry.” We hate to be the bearer of bad news, but every concrete basement wall has significant levels of moisture present in it. If you were to look at concrete under a microscope, you’d be surprised to see how many small voids or “pores” exist in your wall. Concrete typically acts like a sponge, and those pores contain lots of water. So, you MUST assume that your concrete basement wall is fully saturated and full of water in order to properly insulate your basement.

Best Basement Wall Insulation Material Options

The secret to successfully insulating basement walls is selecting insulating materials that stop moisture movement into the house and prevent mold growth as well. Basements are the perfect location for foam type insulation materials. Cellulose is also an option for basements, but it’s not a product that we will cover here.

Spray Foam Insulation

Spray foam is considered the best basement and damp insulation material. Closed-cell spray foam is the best for locking “out” the water vapor that inherently wants to migrate from your damp basement walls to your finished basement rooms. Spray foam provides several benefits, including additional structural stability, easily covers pipes, great vapor barrier, wires, and other utilities, and it provides exceptional R values. The challenge with spray foam is its high price, and it’s a very messy task. However, if you can afford the cost and mess, then this is the ultimate basement insulation product.

Foam Board Insulation

The next best basement insulating method is the use of foam board products. Foam board insulation is a bit cheaper compared to spray foam insulation, so it’s an attractive alternative for many. There are lots of foam board materials on the market, and it would thus be best if you weigh your options carefully.

The key to applying foam board insulation is choosing the correct thickness and sealing it correctly to create an effective vapor barrier. If you’re just going to use foam board, then you’ll most likely require 2 to 4 inches in thickness depending on local energy code requirements in your state.


Insulation of Basement Walls

Basement wall insulation preparation


Fiberglass and Hybrid Foam Insulation

Fiberglass and hybrid foam board insulation is very economical and will perform well in basements that don’t have visual signs of water infiltration. However, this method should NOT be used if you have a history with water, even small amounts.
In this method, you’ll be installing a layer of foam board, sealing it as noted above. Then you will frame a wall in front of the foam board. Lastly, you’ll install fiberglass insulation in the stud cavities. Again, the key point here is to come up with the proper R-value based on local energy codes. Most references suggest that you should NOT use a vapor barrier over the fiberglass insulation in this basement insulation method. Some agree with this, but it’s certainly a gray area.

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