How (and Why) to Insulate a Concrete Floor

Basements are notoriously damp and cold, especially in older homes. Whether you use your basement for storage, laundry, or a bonus living space–or all of the above–choosing to insulate a concrete floor will benefit you in a variety of ways. 

Here, we look at why insulating concrete floors is so important and offer tips on choosing and installing concrete floor insulation.

Why It’s Important to Insulate a Concrete Floor in the Basement

Three key benefits of insulating the concrete floors in the basement are heat loss prevention, moisture prevention, and a higher level of comfort.

Heat Loss Prevention

An uninsulated or under-insulated basement floor is a major source of heat loss in the home. The basement walls and floors of older homes are generally uninsulated. In these homes, the basement accounts for one-third of the home’s heat loss. Adequate basement floor insulation can reduce this heat loss, improving comfort, conserving energy, and lowering your utility bill.

Modern basements built to code are generally insulated, but more often than not, inadequately so. Although building codes differ by region, builders typically use R5 and R10 insulation under the concrete slab, but floors insulated with R20 contain the heat in your basement far better than those insulated with lower R-values.

However, even a newer slab insulated with R-20 may not be adequate, depending on a few factors, including the type of ground your home is built on. For example, if your home is built on rock, heat will be drawn from your home more quickly and easily than if it’s built on clay. Heat will move out of your home more quickly through clay than it will through soil. Consider what your home is built on when choosing insulation for the basement floor.

Moisture Prevention

Although concrete appears to be pretty solid, it’s actually quite porous, and moisture from the ground easily permeates it. Any flooring laid directly on top of the concrete, whether carpet, laminate, or vinyl, will be affected by moisture that seeps through. This may manifest in mold, mildew, or water damage. Insulating the basement floor starts with laying a vapor barrier, which is a sheet of 6-millimeter polyethylene designed to keep moisture at bay. Some concrete insulation panels are made with a vapor barrier already attached, which makes a DIY job easier.

Greater Comfort

Insulating the basement floor before installing finished flooring dramatically improves the comfort of a basement living space. Hard flooring laid directly on concrete is often very cold and tends to suck up the heat around it, making the basement feel cold even when you’ve got the space heater on or the fireplace going. For the highest possible level of comfort, consider installing radiant heating mats before putting down your finished floors. 

How to Choose the Right Basement Floor Insulation

The type of insulation you use in the basement will depend on a number of factors. The most important is ceiling clearance. Most building codes require a basement ceiling height of six to seven feet, and some types of concrete floor insulation add more height than others. 

When Ceiling Height Isn’t an Issue

If you have enough clearance in the basement to add a few inches of height to the floor, one of the most effective ways to insulate the floor is to first install a sheet of polyethylene as a vapor barrier over the concrete, extending it about three inches up the walls. Then, lay down a layer of rigid foam insulation and seal the seams with Tyvek tape or something similar. Install 3/4-inch pressure-treated sleepers, which are long, evenly-spaced planks of wood to which the sub-floor will be nailed. Glue the sleepers down with foam board adhesive, and use masonry nails to attach them to the concrete below the insulation. Finally, install a sub-floor of 3/4- or 5/8-inch exterior-grade plywood or OSB panels, nailing them to the sleepers. Install your finished flooring of choice on top.

When Ceiling Height is an Issue

If your basement has low ceilings and you can’t afford three or four inches, or if you want to simplify the insulating job, opt for an insulated subfloor panel system. Specialty subfloor systems consist of rigid foam insulation sandwiched between a vapor barrier on the bottom and a sub-floor material like plywood or OSB on top. This all-in-one product comes in tongue-and-groove panels that snap together over the concrete. Different types of specialty subfloor systems have different height profiles, but they’re all generally much lower than the height of an insulated subfloor installed on sleepers.

Installing Radiant Heating in the Basement

A radiant heating system installed on top of the subfloor will send heat up through your floor, keeping you toasty during the cold months of the year. Electric heating mats can be used with laminate and vinyl plank flooring, carpet, and tile, which are installed directly over the mats as a floating floor or glued down with adhesive. Wires from the mats connect to a wall thermostat that controls the heat.

Flooring Options for the Basement

Although concrete floor insulation helps reduce water and moisture damage, they don’t completely eliminate the risk. This makes carpet a less-than-ideal flooring for the basement. But if you’re looking for a cozy family room vibe, hard flooring topped with thick, comfy rugs provides versatility and comfort.

Flooring options for the basement include luxury vinyl planks and laminate flooring, both of which are extremely durable and water-resistant. Vinyl plank flooring closely mimics the look of wood or stone, but it’s less expensive and easier to install. Laminate flooring offers a more authentic hardwood look than vinyl planks, and it’s very easy to install and maintain. Both of these flooring options are installed as floating floors, which means they’re not glued down but rather snap together directly on top of the substrate.

Insulating the basement floor is a fairly straightforward DIY project. Once you adequately and properly insulate a concrete floor, your comfort level will go up while your heating bills go down. As always, using high quality materials will produce the best results. Follow the manufacturer’s directions, and have everything you need at hand before you begin.