How to insulate a pre-existing concrete pad

How to insulate a pre-existing concrete pad

Are you looking for information how to insulate your existing concrete slab? Or maybe you 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 you’re installing insulation afterwards, you need to set up proper conditions so it won’t cause trouble.

When insulating concrete floors that are already built, you will have to employ sleepers and install floor planks. You’re basically going to insulate 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, first, we 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.

The reason we check regional value is that the R-value will vary depending on climate. Cold places will naturally need more insulation than warm etc.

Few things about R-values before we begin

Most floor R-values range from 11 to 22. In order to get the best return on your investment is sure to get the proper R-value. Do not over or under insulate otherwise you will be defeating the purpose of insulating the concrete pad in the first place.

Measure the surface area that you are planning to cover and be sure to 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

In order 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 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 our concrete pads surface. Once the floor is good 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 at all so a dry smooth floor is imperative for success. As waterproofing compounds can vary be sure to apply them to the floor using the waterproofing manufacturer’s instructions. After waterproofing is done, we need to let it dry the time it says on the product.

After the concrete pad has been properly prepared take out the roll of polyethylene and lay it out lengthwise being sure to cover the entire surface of the floor. 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 proceed to 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 layout the rigid insulation boards.


It’s important 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 the use of rigid insulation boards. If this is the case in your area, alternative insulation materials will have to be used. Consult with your local building code enforcement agency or insulation specialist for clarity.

Expanding room

When fitting the rigid boards be sure to so allow some room for the board to expand and contract during extreme temperature changes. Insulation that has no room to breathe coupled with extreme 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 in such a way so as 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. At this point, 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 they surely are a good fit for this project. I’d even outsource the project if I didn’t feel comfortable doing it. Insulating or sealing a bad concrete pad can lead to future troubles as well so it’s good to consult professionals about the topic.


This is one way to insulate a pre-existing concrete pad. To do it like this, the concrete slab should be healthy and moisture shouldn’t be a problem. If the moisture gets through the waterproof, it will cause problems in the wood naturally.

What does it mean to anyone who wants to insulate their floors? You should be sure it will work before committing money to a project like this. A lot of houses are actually built like this and there are problems with some of them.

The slab might have sunken or the water around the house isn’t getting out in a controlled way. In such a situation careful inspection needs to take place before committing money to the project.

On the other hand, if you have a healthy slab and you know you’re good to go, there’s nothing stopping you from getting little extra comfort. We all like to walk and spend time in the comfort of warmth. When you insulate an unheated concrete floor, it should also bring down your energy bill.

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