How To Insulate A Floor From The Top

How To Insulate Floor From The Top

There are several good reasons you would want to learn how to insulate a floor from the top. One of the most common reasons is when you have concrete floors in your home. Unlike hardwood floors that have some kind of crawl space underneath and can take a wide variety of insulation, concrete floors only have one solution – insulation from above. Of course, this is assuming the insulation was built-in as part of the subfloor itself.

Learning how to insulate a floor from the top involves working with materials that can act as buffers between the floor itself and the rest of the room. This involves materials such as plywood and filling in gaps using rigid foam insulation, then layering all that with a nice thick carpet.

This is undoubtedly a simple and effective approach. Here are the steps you have to take to achieve this kind of floor insulation from above so it can also act as an air barrier and prevent heat loss during the winter.

Step-By-Step Guide To Insulating A Floor From The Top

Whether you are converting your garage into an extra guest room or just tired of walking into a house with ice-cold concrete floors, insulating that surface is the answer. While there are several complicated alternatives to this solution, professional contractors often advise DIY enthusiasts to choose the simple and most effective option. One that won’t cost too much time, too much money, and doesn’t call for too much technical know-how. That’s exactly what this option represents.

Step 1: Gather The Tools And Materials

Although this step often goes without saying, many DIY enthusiasts skip it with the notion that they will get what they need when they need it for their concrete floor insulation. The problem with this approach is that it wastes too much time (all those trips to the hardware store take a lot of time), and you might improvise with tools that aren’t always the best.

That being said, here’s a list of the equipment and materials that you might need:


  • Circular saw
  • Concrete trowels
  • Screw gun
  • Tape measure
  • Utility knife
  • Sawhorses


  • Leveling compound
  • Threshold or edging strips
  • 6-mil polyethylene sheeting
  • Construction tape (heavy-duty)
  • Compression grade rigid foam insulation (as needed)
  • 1/2-inch plywood sheets (exterior-grade)
  • Utility screws (outdoor-grade and corrosion-proof)

Step 2: Repair And Clean The Floor

Before you start insulating the current flooring, you need to make sure that it’s in good condition. This means inspecting the flooring and repairing it as necessary. If all it has is a few minor cracks and some unevenness, you can take care of that with a leveling compound. Once all the repairs are done, make sure that the flooring is thoroughly cleaned.

Step 3: Cover The Floor With A Vapor Barrier

If you are going to insulate a concrete floor from above, one of the most important steps is to lay down a vapor barrier. This barrier is designed to prevent moisture from seeping through and up into the room through the concrete floor beneath.

The vapor barrier is simply a layer of 6-mil polyethylene. When layering this vapor barrier over the solid floor, be sure to overlap the seams. A good approach is to overlap the seams by about 6 inches and then seal them using waterproof construction tape. Once that is done, run some of the polythene up the wall for maybe 4 inches and use construction tape to secure that to the wall.

Step 4: Lay The Rigid Foam

Once you have the polythene secured onto the floor, the next step is to lay the high-density rigid foam insulation board over that polythene. Again, you can use a hacksaw, drywall saw, or even a utility knife to cut these down to the appropriate size for your underfloor insulation. Be sure to leave about a 1/4-inch space around the perimeter before taping the seams of the high-density foam using heavy-duty construction tape.

Step 5: Lay Plywood Panels

The next step to your rigid insulation is to lay down your exterior-grade plywood sheets over the rigid insulation foam. The idea here is to make sure that the plywood sheets are running perpendicular to the foam that the seams aren’t aligned.

In this case, you want to space the plywood panels at 1/4 inches apart and leave at least 1/2-inch space around the perimeter so that the plywood sheets have some room when they inevitably expand with temperature changes.

Once the first layer is complete, lay another layer of plywood sheets on top of that one; this layer should also run perpendicular to the first one using the same spacing. Once that is done, fasten the two layers using 7/8-inch utility screws (outdoor).

Step 6: Install Transitions Or Carpet

Depending on the location of the concrete slab or floor you are insulating, you will have to either install transitions for the floorboards or carpet. If you are simply transforming your garage into a livable space and you might still want to use it as a store for your vehicles, then you might want to install transitions. Otherwise, installing a nice thick carpet over your work will finish it off nicely.

Why Insulate Floors From The Top?

You might be wondering why you need to go through all this trouble while you could simply buy a thick rug or carpet and lay it over the floor. The truth is that, while the rug or carpet will probably do the trick, they can only do so much.

During those very cold winter days, the frigid temperatures tend to seep through the ground, especially when it’s concrete. To protect against this, you will need more than just a layer of cloth or rug. Besides, these solutions don’t have the all-important vapor barrier that ensures the cold doesn’t get through.

This is how to insulate a floor from the top. As you can see, it’s a simple enough process that doesn’t call for extensive technical know-how, nor does it need you to confirm with your local government whether or not you need a permit. It’s a project that can be done over one weekend if you call over a bunch of friends.