How To Insulate A Concrete Floor

How to insulate under concrete

Most modern homes with concrete floors should have had insulation installed during construction, typically with a thick layer of polystyrene in sheets between the hardcore base and the completed surface. This insulation layer could be missing from solid floors in older homes; however, it is undoubtedly worth considering installing concrete floor insulation if your home is feeling cold or you want to reduce to reduce your heating bills and carbon footprint.

At a time of high heating costs, it is prudent to ensure that your home is adequately insulated. While the cost of retrofit insulation on a concrete floor can be expensive, costing anywhere from a few hundred to several thousand pounds depending on how much insulation is required, the savings generated each year will mean that your investment is more than worthwhile.

How Does Floor Insulation Work?

Heat loss through flooring is more apparent in homes with solid concrete ground floors, which are commonly found in newer build homes. They can be insulated by laying rigid insulation boards on the flooring. Internal insulation can also be installed, but this requires replacing the concrete floor, which is best done when the floor already needs replacing.

Suspended timber floors are typically found in older homes. If your home has a suspended timber floor, you will most likely notice that you have air or ventilation bricks on the outside walls below floor level. Inserting insulation into these air bricks to seal the holes may seem to be the obvious solution; however, this is something that you should never do.

Lifting the flooring and laying insulation between the joists is required to adequately insulate timber floors, which an insulation specialist best does. By sealing gaps between the floors and the skirting boards, you can limit heat loss by draught-proofing, reducing cold air and drafts.

Laying Insulation Boards on Top of Concrete Floors – Pros and Cons

There are insulation boards available that can be installed on top of an existing floor or embedded in the floor. Here are some points to consider before using this method.

Pros of Insulation Boards

  • Simple to handle – Insulation boards are very light, easy to manoeuvre, and simple to cut to size.
  • Rapid Room Warming – By placing insulating boards over the concrete floor, the room will warm up quickly.
  • Versatility – Insulation boards can be installed over suspended timber flooring and concrete.
  • Levelling Floors – A coating of insulation can aid in the levelling of unevenly finished concrete floors.

Cons of Insulation Boards

  • Thickness – Many insulation boards are approximately 50mm thick, boosting the floor.
  • Not a finished surface – You will need to add height by laying a chipboard sheet over the insulation boards.
  • Room Alterations – Consider increasing skirting boards, trimming doors, and even shifting plugs.
  • Price or Materials – Good quality insulating boards are not inexpensive. You’ll also need chipboards and a damp-proof coating.
what is insulation under concrete
Image: Insulation under concrete

Laying a Floating Floor

A floating floor is created by laying boards on top of an existing concrete floor to level the surface, add insulation, or both. Here is the simplest and most popular DIY floating floor installation method.

Step 1 – Preparing the Floor

If you want to insulate a solid concrete floor in a finished room, you will most likely need to remove the existing skirting boards. After that, ensure the floor is stable, dry, and clean. Next, repair any cracks in the concrete. Finally, if it’s wet, figure out where the moisture is coming from and fix it before moving on.

A concrete floor sealer may be necessary if the concrete is starting to crumble or flake.

Step 2 – Installing Floor Insulation Boards

Measure the width of the floor and cut the insulation board to the appropriate length. You don’t have to cut the first one if the room is wider than the board is long. Place the first insulation sheet in the corner of the room farthest away from the doorway.

Insert it tightly into the corner. If the board is too short, measure the distance between the end of the insulating board and the wall and cut a section of the board to fit. Place the next insulating board against the cut end, so the joints are somewhat staggered instead of running straight across the room. As you lay each board, make sure they are closely pressed together.

Step 3 – Installing the Damp-Proof Membrane

You can proceed to the following stage once the room has been entirely covered with an insulating board. A damp-proof membrane is not required; however, it is recommended (considering the minimal cost, there is no real reason not to add one).

The damp course membrane must be cut wider and longer than the room to lap up against the walls. You may need to cover the floor with several damp-proof membrane sheets; if this is the case, it is recommended that the joints overlap by at least 300mm, and then seal with waterproof tape.

Step 4 – Laying the Chipboard

Lay the first sheet of tongue-and-groove chipboard at the corner of the room farthest from the doorway. Allow an expansion gap of approximately 10mm around the room between the chipboard sheet and the wall. Apply the proper glue to the tongue of the initial chipboard sheet before inserting the second.

Joints should be staggered where sheets have been set end-to-end, just as you did with the insulating board. There should be no need to use screws or nails in the boards. Wipe away any residual glue from the joints before laying the remaining boards.

Step 5 – Fitting Skirting Boards

You can now install skirting boards around the room. Trim the overlapped membrane to 20mm above the chipboard floor if it protrudes too far. Before attaching it to the wall, ensure it is placed behind the skirting boards.

The skirting boards will conceal the expansion gap you left around the room. You should contact a qualified electrician if plug sockets need to be raised.

Solid Floor Insulation – Alternative Options

The approach described above is the most effective way to insulate a concrete floor without the need for digging it up and re-laying it with insulation placed beneath the finished surface. However, it is not cheap and might cause other issues, such as excessively raising the floor level.

Lining a concrete floor with chipboard sheets and carpeting over it is a less expensive and easier way to insulate it. In addition, a high-quality rubber underlay will further increase the feeling of warmth. Of course, this will not be as effective as proper insulation; however, it will make a difference.

Ground-floor floors, walls, and roofs are common areas where a building can lose heat, and while floor insulation often refers to adding insulation material around floor space on a property’s ground floor, when you have floors on upper levels above unheated areas, such as a garage, you may lose heat here, and these floors may also need insulation.

On This Page
Get Your Insulation Quote