Types Of Floor Insulation

Most insulation products can be used to insulate floors. Choosing the right type of insulation directly affects the result. 

Why Insulate a Floor?

Floor insulation is important for several reasons:

  • Reduces energy consumption–saving money.
  • Reduces drafts along the floor.
  • Increased comfort in the living area.
  • Helps with moisture control–reducing mold, pest, and rot problems.
  • Increased soundproofing between living areas.

7 Floor Insulation Options

7 Common Floor Insulation Products

Concrete floors and suspended timber floors often require different insulations to be effective. Most of the following products can be used on both.

1. Fiberglass

Fiberglass batt insulation is often the most popular type of insulation. It is cheap, effective, and easy to install between open floor joists. Strapping is usually required to prevent it from falling out. Fiberglass absorbs moisture and needs a vapor barrier. Encapsulating a crawl space is a better option than insulating but it is more expensive.

Fiberglass can also be used as insulation on a concrete floor if the floor is being built up. Lay a vapor barrier down first.

2. Spray Foam

Spray foam insulation is one of the best and most complete options available to insulate the undersides of suspended timber floors. It seals all gaps and cracks and has an R-value of R-6.3 per inch. It is waterproof and does not support mold or pest infestations. DIY spray foam kits are available online or from home improvement outlets. Or it can be contractor-installed. Spray foam can be used between sleepers on a built-up concrete floor without a vapor barrier.

3. Cellulose

The wet form of cellulose insulation can be sprayed onto the undersides of suspended timber floors. It stays where it is installed and will not fall off when dry. The wet spray application fills gaps and voids around pipes, wires, and framing members. Wet cellulose application is not a DIY project.

Loose-fill cellulose can be installed from above by removing the flooring and subfloor. Netting or 6 mil poly is installed between the joists and cellulose installed. Subflooring and finish flooring are then replaced.

Loose cellulose can be installed over concrete–between the seepers of a built-up floor. Install a vapor barrier first.

5. Rigid Foam

Rigid foam board insulation like extruded polystyrene and polyisocyanurate qualify as a vapor barrier if they are at least two inches thick. Cut to the proper size, they can be used on concrete and between floor joists.

The boards can be friction-fit between joists from above or below. They can also be nailed or screwed to the undersides of joists. A can of spray foam or a tube of acoustic caulking can be used to fill any gaps.

5. Mineral Wool

Mineral wool insulation batts can be used in the same ways and places as fiberglass batts. Mineral wool absorbs less moisture than fiberglass but still requires a vapor barrier. It has very good soundproofing abilities and is often specified as insulation between floors and walls in apartments and office buildings.

6. Insulating Screed

Insulating screed may be the quickest, cheapest, and least intrusive floor insulation. It is a mixture of concrete and expanded polystyrene beads, perlite insulation, etc. Screeds can be applied over concrete, wood subfloors, rigid foam boards, and even sand to level the floor and provide extra R-value and soundproofing.

Insulating screed is applied by contractors or as a DIY project. It is lightweight and eliminates thermal bridging. Provides the ideal covering for basement floor heating systems.

7. Carpet

Heavy carpets or area rugs with thick heavy underlay provide good insulation value and soundproofing. Flooring underlay like QuietWalk Plus acts as a vapor barrier for carpeting laid on concrete floors.