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How Do I Choose the Best Insulation for Floor Joists?

Selecting the best insulation for floor joists hinges on R-value, material compatibility, and climate considerations. High R-value options offer superior thermal resistance, while moisture-resistant materials prevent mold growth. Reflect on your regional weather patterns and consult a professional to match your needs. What factors will influence your choice for a cozy, energy-efficient home? Join the discussion below.
Dan Cavallari
Dan Cavallari

The idea that heat rises has prevented many builders in the past from insulating floors, but adding insulation for floor joists can actually improve a home's energy efficiency as well as its insulating capabilities. Part of the problem with adding insulation for floor joists is securing such insulation between joists underneath the floor. Batt insulation can be used, but it will need to be secured in place properly; blown-in insulation is also an option, though this can be messy and somewhat inefficient. Aluminum sheeting can also be used to insulate between joists, but this may not be the most efficient method for floors.

If you choose to install insulation for floor joists, it is best to first examine your floors and joists carefully. You will be at an advantage if you have a basement or crawl space, as installing batt insulation properly will be much easier. Otherwise, floorboards will need to be torn up in order to install insulation for floor joists properly. It may be possible to blow insulation into a small access panel or crawl space in order to properly insulate the floor, but this can be costly, and you will probably have to hire a professional to do it. Blown insulation can be messy and can coat pipes, wires, and other common items within floor spaces, and gaps may exist within the insulation, leading to heat loss.

View of second story floor joists from below.
View of second story floor joists from below.

In attics, aluminum sheeting is often used for insulation, and this same method can be used for insulation for floor joists, but this will not be the most efficient method for retaining heat within the home. It is inexpensive as compared to other insulation methods, and it is relatively easy to install, but the benefits may not outweigh the cost and labor. Aluminum sheeting is fairly lightweight, but it can also be damaged fairly easily.

Floor joists on new construction.
Floor joists on new construction.

Fiberglass insulation is usually the best option, though handling fiberglass can be dangerous and it is not the most eco-friendly option in some cases. Fiberglass rolls can be placed between joists, but the fiberglass itself will need to be cut to fit properly between joists. The insulation should press right up against the floor between joists; gaps between the insulation and the floor can lead to inefficiency and heat loss. The fiberglass will also need to be secured in place using wire mesh, twine, wood laths, or other securing methods, which can be an intensive project that adds to the overall cost.

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Discussion Comments


A wood floor gets cold. That's a fact. A layer of carpet is a good way to provide a layer of insulation from the cold outside air. Also, the carpet feels better beneath your bare feet than the wood. You can also use area rugs, but this is not nearly as good for obvious reasons.


@Feryll - I'm sure the batt insulation under the house will help reduce the problem with cold floors some, but maybe the real problem is not the lack of insulation under your floors. I was told that cold floors are a sign that the foundation of a house is not well sealed.

Many houses have vents in the foundation. This is a way cold air can get beneath a house and cause cold floors. The better insulated or sealed the foundation of a house is the less of a problem cold floors will be. I had an old house with a brick foundation, and there were some good sized cracks in some of the bricks and in the mortar.

Once I got the cracks filled in, I noticed an immediate improvement in the comfort level inside the house. I never did add any insulation directly to the floor joists.


We have cold floors. When the temperature drops outside the wood floors tell the story. We were told that we could install batt insulation under the house and that would help keep out cold air and keep our rooms warmer. Our real estate agent says she has done this with several of the old houses she renovated.

I have seen the batt insulation at the home improvement store where we shop. The good thing about the batt insulation is that we can buy small amounts as we can afford it, and I can crawl beneath the house and attach the insulation to the underside of the floors. This is relatively easy, and we don't have to pay anyone to do the job for us. This part is a bonus.

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    • View of second story floor joists from below.
      By: Howard Sandler
      View of second story floor joists from below.
    • Floor joists on new construction.
      By: Gord Webster
      Floor joists on new construction.
    • Batt insulation may be used for floor joists.
      By: brozova
      Batt insulation may be used for floor joists.