Insulating your floor

This page is about insulating your ground floor. For advice about other sorts of insulation go to the Insulation FAQ.

I have suspended floors and they are cold and draughty. How can I stop the draughts and insulate?

Suspended floors are often draughty because there is a howling gale blowing through the space below the floorboards. The floor joists must be vented from below so you must have air bricks allowing free air flow beneath the floor. However, you don’t want that chilly breeze coming up into the living room. Draughts can seep in between the floorboards and also under or behind the skirting boards. Insulation will help but it is best to seal the draughts separately.

You should insulate your floor before you seal it otherwise you will have to break the seal again to get underneath. This story from Cambridge Carbon Footprint (pdf) explains very well how to insulate below a suspended floor. Ann and Tom describe their experiences coming at it from all angles – taking up the floor above or crawling underneath. They also talk about how they decided what materials to use. You can also consider under floor heating.

You do not necessarily have to take up the floor in order to insulate it. Some installers such as Q-bot use robots to spray foam insulation from underneath. This will stop draughts as well, as part of the process.

Alternatively, you can stop up draughts yourself. You can use just a sealant if the gaps are very small. However, for anything bigger you need to fill them first. Here is a review of some products for sealing between your floor boards from the Guardian. The cheapest option is to use old newspapers to make papier-mache as a filler between the boards.

For skirting boards you will almost certainly need a filler as well as a sealant. This video has a good description of the traditional technique. The demonstrator uses a foam core for a filler and then applies a sealant over the top. You can use silicone or a more traditional caulking. Alternatively, you can use caulking strip similar to window draught sealing strip.

There is an excellent guide here (Get Energy Savvy) with thermal pictures of the draughts as well.

I have solid floors. Do they need insulating too?

Solid floors are often a problem for heat loss. If your house is otherwise reasonably insulated you could be losing 15-20% through your solid floor. Check out the house heat loss model for an estimate for your house.

If you are installing external wall insulation around a room with solid floors it is a good idea to take the insulation below the floor level for a foot or so to stop heat leaking out sideways from just under the floor.

Insulating solid floors is very disruptive. Either you have to lay insulation over the concrete which raises the floor level – you have to adjust skirting, wiring, doors and door steps everywhere - or you have to excavate the floor to make room for the insulation. The good news is that you don’t need so much insulation to get a low U-value as you do for walls and lofts. This is because the ground does not conduct heat away as fast as the air. You may be able to get away with only 40mm of insulation to get a reasonable U-value. The Superhomes website has some good advice on this.

If you are excavating your solid floor it would be good idea to consider under floor heating at the same time. It may or may not be right for you but it is something to consider.

With underfloor heating:

  • You don’t need bulky radiators because you use the whole floor area.
  • You get the heat at floor level so it warms your feet nicely.
  • It does not require such high temperatures as conventional radiators because the surface area is so large. This reduces the drying effect that can make some people uncomfortable and contribute to breathing problems. Also it gives you the option of installing a heat pump instead of a conventional boiler.
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