Insulation of Timber Floors

Insulation of Suspended Timber Ground Floors

Very often, when people are insulating a house, they insulate the roof space, double glaze the windows but forget to insulate the floors. If the rest of the room is insulated, the floor becomes a thermal weak point. A solid ground floor is difficult to insulate retrospectively.

However, if there is enough room to increase the height of a floor slab or if it is a suspended concrete slab construction, one can sometimes get access under the floor making it possible to improve insulation.

A suspended timber floor can often be insulated and, depending upon the space under the floor, the floorboards may not need to be removed and the job can be carried out within a day.

These floors often let in drafts between the floorboards from the under floor airbrick ventilation that needs to be there to allow the timbers to dry out and to ventilate the under floor cavity.

Such floors can be insulated below the timbers by insulating the space between the joists. This insulation sometimes needs fastening with battens or similar to hold it in place.

Under the joists, a sheeting material such as Airtec, which is like bubble wrap with foil to one or both sides, can further be used and simply stapled to the undersides of the joists. This will provide thermal insulation and, as a bonus, sometimes removes musty smells where present.

It is important to check that the ends of the joists can breathe if they are set into solid walls without damp proof courses or other protection. Should no access be available to the under floor void, insulation needs to be applied on top of the floor or by lifting the floorboards and “dropping” the insulation down (ie. suspending) the insulation between the joist and then relaying the timber floor.

Arguably the least disruptive way to improve the internal environment while occupying a property is to adopt a thermal underlay to a carpet to improve the internal environment. This is less thermally beneficial but to some this would be the easiest method of improving the insulation.

Should you wish to obtain advice on the application of insulation to floors, many competent builders would be happy to advise. Some DIY stores and builders’ merchants may also be able to offer advice including Advice Sheets explaining the principles.

For a larger floor, or where the job requires professional input or supervision, do not hesitate to consult your local independent chartered surveyor on the website.

November 2009