How to insulate a concrete floor?

If you want to insulate an existing concrete floor, the easiest way is just to put insulation on top of the concrete. Keep in mind that the floor level will rise which may cause issues with building regulations due to unequal step heights at staircases and elevated step heights at external doors. This method may also cause a problem for doors which may need to be reduced in size due to the raised floor level. You also may need to reduce or adjust skirtings and radiators accordingly. If you’re planning on insulating concrete, you should always do it before installing flooring, because adding insulation adds a couple of inches to your floor.

There are many methods for concrete floor insulation. Most of them usually depend on cost and headroom for insulation. If you are finishing a basement, the basement headroom building codes are usually around 7” of headroom so you have to keep this in mind when choosing insulation for sub-floors. There are two main ways of insulating concrete. You can cover the concrete with rigid foam insulation, add two layers of plywood and add the finish flooring or you can attach wood sleepers to the floor, fill the gaps with rigid foam insulation, apply a subfloor and finish flooring.

Before insulating concrete, it is essential to control moisture bleeding through the concrete. Although concrete looks like a solid rock, it is actually very porous. Ground moisture easily migrates through the slab and affects whatever is on its surface. Moisture control is crucial even for the concrete in your garage that won't get insulated. Moisture control can be done by using exterior-grade plywood sheets laid over the foam for example.

When installing a rigid foam board, you should follow these 7 steps:

• Repair and clean flooring
• Install vapor barrier
• Add foam board insulation
• Tape seams on foam board
• Add sleepers or plywood
• Add flooring or plywood
• Add thresholds as needed

Repairing and cleaning the flooring is a crucial step in properly installing house insulation for concrete floors. After installing insulation, it will be very difficult and expensive to make any repairs or cleaning of the concrete flooring beneath. The concrete flooring must be level to avoid any sagging, cracks, or imperfections that will persist through the insulation. That's why it is very important to clean and fix your concrete flooring before taking any other steps. If you have cracks in your concrete, you can use a concrete patching material to fix them.

After cleaning and repairing the concrete flooring, the next step is installing a vapor barrier due to the fact that concrete is very porous. Without a proper vapor barrier, the moisture will leak onto the upper layers of the insulation and can even damage the flooring.

The next layer after the vapor barrier layer is the main insulation layer, in our example the rigid foam board layer. Adding more than one layer increases the total R-value, thus lowering utility bills and increasing savings. The idea is to cover 100% of the floor, and that will probably involve cutting the foam boards in all sorts of sizes to make them fit the best. When cutting, leave about ¼ of room on all of the edges to account for expansion and contraction.

After laying down the foam and covering the entire concrete floor, you should cover up the seams with tape. It’s important to use heavy-duty construction tape. Duct tape or other household tapes just won't cut it in terms of strength and durability for this application.

The next layer is a choice between sleepers or plywood. You may end up asking yourself how much material do I need? ¾-inch pieces of lumber called sleepers will be enough to hold the subfloor and flooring up. If the wood is pressure treated it will last longer because it will be in close proximity to concrete. If opting for plywood, you need to make sure to use exterior-grade material. You usually need to use ½-inch plywood, two layers of plywood of this thickness are considered the best. Alternating the direction of the plywood from one layer to the next provides a much more solid final subfloor. For the first layer of plywood, you can simply lay it on top of the insulation. Foam board adhesive and/or masonry nails may be appropriate if you are having trouble getting it to lay flat.

After adding sleepers or plywood, the next thing to do is to add a subfloor or flooring. If you don't need a fine flooring, you can alternatively just finish the plywood with paint or stain. You can now add the flooring or subflooring as you would over wood framing, because of all the prep work. Be sure to cut the plastic vapor barrier that runs up the walls before placing flooring or subflooring.

The final and optional step is to add thresholds if needed. Thresholds help doors transition from the old flooring to new flooring smoother, because after all these steps you’ve added a few inches to the floor. Premade thresholds are easy to find for the most common heights, but you may be in a situation where you need to make a frame yourself.

There are three main benefits of installing insulation on the concrete floor of your basement: heat loss prevention, moisture prevention, and a higher level of comfort.

Heat loss prevention is probably the most significant benefit of insulating your concrete basement floor. Uninsulated basement floors are a major source of heat loss in homes. The basement in older homes in which the floors and walls aren’t insulated generally accounts for a third of the home’s heat loss. Adequate concrete floor insulation like under concrete prodex will greatly help in reducing heat loss, improving comfort, conserving energy, and lowering the utility bill.

Moisture is a big downside to concrete. Even though it looks solid, it is actually very porous, thus moisture can easily penetrate it. Any flooring laid directly on top of the concrete-like carpets or wood flooring will be susceptible to moisture buildup. Proper insulation of concrete flooring can help eliminate its moisture problem.

Insulating basement floors can drastically improve the comfort of the flooring. Walking on wood is much more comfortable than walking on cold, hard concrete, wouldn’t you agree? Hard concrete flooring can get very cold and is known to suck up the heat around it, making it feel colder than it actually is.

The most common types of insulation for concrete floors are:

• Radiant foam insulation (under concrete prodex)
• Rigid foam boards
• Fiberglass floor foil

• Plastic film vapor barriers
• Plywood or sleepers
• Flooring or subflooring

Radiant floor insulation and installing radiant heating can help in making concrete floors warmer. Radiant heating solutions are installed on top of subflooring to keep you warm in the coldest months of the year. This is a very effective method of making your concrete floor warmer, but with proper insulation, you may not even need radiant floor heating.