How You Insulate Under Floorboard Insulation

When your home is old or has no under floorboard insulation adding it can make a big difference to your comfort and save you money on energy bills. But under floorboard insulation isn’t the whole story and to get full benefits you need to also seal draughty doors and windows.

How You Insulate Under Your Floorboards

The most convenient way to install underfloor insulation is in an accessible space, like a crawl or basement, where you can fit blanket batts or rolls of mineral wool, foil-faced polyisocyanurate or rigid foam. This is a job for a professional installer as it involves drilling through floorboards and fitting new ones, as well as installing a vapour permeable airtight barrier (to stop moisture from entering the joists).

In older houses with suspended timber floors you may be able to insulate from below without taking up the floorboards. In this case you can friction-fit semi-rigid insulation boards or slabs, or tack tongue-and-groove wood-fiber board to the undersides of the floorboards. Alternatively, a layer of netting can be fixed to the undersides of the joists and then filled with quilt or cellulose insulation to form troughs. The netting is then tacked to the insulation to hold it in place.

It is possible to insulate a suspended timber floor from above, but this is a more disruptive option. You would need to lift all or some of the floorboards, and if you have old floorboards that are valuable aesthetically or historically, this might not be an option.