How to insulate a pre-existing concrete pad

How to insulate a pre-existing concrete pad

Are you looking for information on how to insulate your existing concrete slab? Or you may have a cold space in your house that you would like to heat now and then.

To do that is not impossible, but you have to be prepared to work and invest a little bit. When installing insulation afterward, you need to set up proper conditions so it won’t cause trouble.

When insulating concrete floors that are already built, you must employ sleepers and install floor planks. You will insulate the raised floor over the concrete floor, as we can’t go under the slab to do that. This will be a simple generalized instruction to achieve that.

How to insulate a floor from the top

Before doing anything else, we first need to check the regional R-value. R-value stands for how well something resists the conductive flow of heat. In this case, it will be the insulation we’ll install.

We check regional value because the R-value will vary depending on climate. Cold places will naturally need more insulation than warm places, etc.

A few things about R-values before we begin

Most floor R-values range from 11 to 22. To get the best return on your investment, you are sure to get the proper R-value. Refrain from over or under-insulating; otherwise, you will be defeating the purpose of insulating the concrete pad in the first place.

Measure the surface area you plan to cover. Add a little extra to your flooring and insulation materials total to allow for cuts and margins of error. I usually take 10% extra if accidents happen and so on.

Materials Needed

To insulate a pre-existing concrete pad, you will first need to assemble the following materials and tools;

Roll of a polyethylene vapor barrier, hammer, masonry nails, 2×4 board, waterproofing compound, brush, and paint roller for applying the waterproofing compound, tape measure, spread out a polyethylene vapor barrier, rigid foam insulation, construction adhesive, and flooring planks.

Installing floor insulation

The first thing that needs to be done is repairing the cracks and holes on the surface of our concrete pad. Once the floor is excellent and fault-free, we can continue with the waterproofing compound to help us prevent future moisture issues.


We do waterproofing as wet insulation is like having no insulation, so a dry, smooth floor is imperative for success. As waterproofing compounds can vary, apply them to the floor using the manufacturer’s instructions. After waterproofing, we must let it dry when it says on the product.

After the concrete pad has been adequately prepared, please take out the polyethylene roll and lay it out lengthwise, ensuring it covers the entire floor surface. The polyethylene will act as your insulation’s vapor barrier.

2×4 sleepers

Next, take the 2×4 boards and lay them on top of the polyethylene in 16-inch intervals. “Sleepers” mentioned at the beginning are the 2x4s. It would be good to measure the distances well, as it will help us when we cut the insulation boards. We can cut even shapes.

Then, we permanently fasten the sleepers to the concrete pad every 16 inches using masonry nails. Once the sleeper boards are securely attached to the floor, it is time to lay out the rigid insulation boards.


It’s essential to measure and cut the rigid insulation boards so that they will fit properly in between the sleeper boards. Then, we can affix them to the polyethylene using construction adhesive.

Note: Some parts of the country have codes that disallow rigid insulation boards. If this is the case in your area, alternative insulation materials must be used. Consult with your local building code enforcement agency or insulation specialist for clarity.

Expanding room

When fitting the rigid boards, allow some room for the board to expand and contract during extreme temperature changes. Insulation that has no room to breathe coupled with radical temperature changes could cause condensation to form.

Floor planks

Once the sleeper and insulation boards are in place, it is time to install the floor planks. As you measure, cut, and lay the floor planks, be sure that you cut them so that the plank joints are centered over the sleepers.

Securely nail the floor planks to the sleepers until the entire surface has been covered. Now, we have an insulated floor on top of our concrete pad. We may or may not want to add a finished floor on top of your new sub-floor. In the case of covering a concrete pad, a finished floor is entirely optional.

Also, one thing to remember is to double-check all the regulations and materials that undoubtedly are a good fit for this project. I’d even outsource the project if I felt uncomfortable doing it. Insulating or sealing a bad concrete pad can also lead to future troubles. Hence, it’s good to consult professionals about the topic.


If you are considering insulating your floors with a pre-existing concrete pad, it’s important to understand the specific requirements of the project. One way to insulate such a pad is to ensure that the concrete slab is in good condition and that issues of moisture are not present. If moisture does penetrate the waterproof layer, it can lead to serious problems with the wood.

Before committing any money to the project, it’s best to make sure that your floors are suitable for insulation. Many homes are built in this way and can present problems, such as sunken slabs or poor water drainage. Therefore, it’s important to carefully inspect your floors to ensure that they are healthy and free from any moisture issues before beginning any work.

However, if you have a healthy slab and are confident that your floors are suitable for insulation, then insulating your floors can provide you with some extra comfort. You can enjoy spending time in the warmth and comfort of your home, and insulating an unheated concrete floor can also help to bring down your energy bills. With proper care and attention, insulating your floors can be a great way to improve the comfort and energy efficiency of your home.