Best Insulation to Use When Insulating Floors

snow shovel by door - best insulation to use when insulating floors

With colder weather upon us, you might be turning your attention to winterizing your home. The average home loses up to 15% of its heated air through floors, so if insulation is part of your winterizing efforts, it’s smart to consider insulating floors, as well as the usual suspects like attics.

This article will walk you through your choices for floor insulation and try to help you find the best insulation for your home.

Flooring Considerations

First things first, though. Know that you needn’t insulate every floor of your home. You’ll only see a benefit from insulating floors above an un- or under-insulated space like a basement or crawlspace.

Also be aware that depending on your home’s construction, you have some choices about where your insulation goes, i.e. under or above floor.

Under floor insulation, as the name has no doubt suggested to you, can be applied where there’s an unfinished space beneath the floor. This is the easiest and most cost-effective way to insulate, and it will give you more options for materials.

Above floor insulation goes in between a subfloor and the finished flooring. The best time for this project, of course, is when you’re already replacing the flooring. If you don’t have access to a space under your floors, however, you can still insulate by pulling up and reinstalling the floor.

When choosing your materials, consider your climate, in addition to the type of access you have to your floors. ENERGYSTAR advises insulating floors to an R-value of R-13 for those of us in more temperate climates, all the way up to R-30, for those of us in the north.

The R-value you need will play a huge role in the cost of this project, so have that information in your mind as you begin to think about materials.

Batts or Rolled Insulation

Batts, or rolls of insulation, are typically composed of fiberglass or mineral wool. They’ll have an R-value of R-3 to R-3.5. Manufacturers will often use paper, foil or other facing as an air or vapour barrier.

Recycled denim insulation, which is a kind of cellulose insulation with an R-value around R-3.5 per inch, is a less carbon-intensive option for those interested in going green.

The advantages of using rolls and batts to insulate floors include their low price tag and ease of installation. Cutting the batts and fitting them between the joists is a straightforward job for a DIYer.

The disadvantage is that you won’t be able to keep the insulation from settling over time, even if you install something underneath it. Eventually, the insulation will simply be ineffective because it will sag away from the floor.

Moisture is another consideration when installing batts. They’re prone to mold and rot when they get wet, which can be an especially big problem when you’re laying the insulation in a damp crawlspace.


cork tree - best type of insulation to use when insulating floors

Cork is an excellent option for above floor insulation, as it reaches an R-value of R-3.6 to upwards of R-4. It comes in semi-rigid boards, which are typically laid underneath flooring material. Cork flooring itself, it should be noted, is not an effective insulator because the tiles are too thin.

Cork is environmentally friendly, extremely long-lasting and straightforward to DIY. The big disadvantage here could be cost, depending on where you live. While cork is increasing in global popularity, it’s not as common in the U.S. as other options on this list.

Loose Fill

Typically made of fiberglass, loose-fill insulation has an R-value of R-2.2 to R-3. Many environmentally friendly loose-fill alternatives are on the market, such as sheep’s wool or mineral wool. Sheep’s wool is more expensive, but has an R-value upwards of R-4.

Cellulose insulation is a more common and less expensive option. It’s usually made from largely post-consumer recycled paper, although loose-fill denim and recycled cotton insulation are also becoming more mainstream. Their R-value (R-3.5) is a bit better than fibreglass, and the increased density of paper insulation makes it better at blocking air leaks.

While loose fill is great for attics, it’s more labour intensive when you’re insulating floors. As with batts, it needs plastic sheeting or some other barrier to hold it in place. Even then, sooner or later you’ll face the same issues with settling as you would with rolls or batts.

Rigid Foam Boards

This type of insulation is made of polyurethane or extruded polystyrene (XPS) and has an R-value of R-5. Facings like aluminum foil are often used as a radiant barrier.

Foam boards are better suited for under floor applications than loose fill or batts. They can be cut and pressed between the joists, and their edges can then be caulked or taped to reduce airflow. Foam boards also have the advantage of being moisture-resistant.

This is a more expensive option, material-wise, and it can be tricky to use around venting and pipes. Polyurethane and polystyrene are also some of the less environmentally friendly materials on the list, although the potential for improving home energy performance could work out to be an acceptable trade-off for you.

Spray Foam

Made from polyurethane, spray foam can have an R-value of R-3.5 for open-cell and R-6 or greater for closed-cell foams.

It’s one of the more effective ways to insulate a floor, since it will adhere to the underside of the floor and can be sprayed around mechanical systems like vents. This makes it much better at preventing air leaks.

The advantages of spray foam also make it one of the most expensive options. A big part of that expense is that you’ll need a professional to apply it. Other cons include spray foam’s poor environmental track-record. It’s energy intensive to produce and install. It’s also recently been made with HFCs, which have very high global warming potentials (GWP).

While HFCs are being phased out, be aware that you’ll still come across them as the industry shifts to less harmful hydrofluoroolefins (HFOs).

Your Best Choice for Insulating Floors

What makes the best option is ultimately up to you and the criteria you’ve set for this project. For us, we think cork is a fantastic option for above floor insulation. For under flooring, consider a spray foam that uses water as a blowing agent and natural oil-based components like soybean or castor oil.

Feature image: Greta Hoffman; Image 1: Mathis Jrdl

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