Insulating A Suspended Timber Ground Floor

Fintan from our technical team discusses the thermal loss issues associated with suspended timber floors and outlines a best practice approach to tackling them.

Insulating a suspended timber ground floor.

All methods of installation. Insulating a suspended timber floor can eliminate floor draughts and reduce heat loss through the fabric of the floor at the same time. Ideally a fibrous insulation such as mineral wool or sheep s wool performs best between timber because it will take up thermal movement and cut down air movement around the insulation. This floor insulation method is commonly used for upgrading the thermal performance of existing timber floors as it has no impact on floor levels.

If the ground floor in question is of a suspended timber construction and whether this is a renovation or new build project then the insulation would normally be installed in the joist zone that is installed between the joists. Side nail 25 mm x 25 mm timber battens to the joists or partially drive galvanised nails into the side of the joists in the appropriate position to hold the boards in place. Why are some suspended floors cold. A best practice approach to insulating suspended timber floors.

The insulation would need to be secured ideally with a taped membrane a vapour open membrane such as solitex fronta wa taped at joints such as tescon vana would be ideal stapled to the underside of the joists to cut. Care must be taken however not to harm the character and significance of the building or impede subfloor ventilation for example by blocking air vents so promoting timber decay. Thermal bypass affects performance so cutting out draughts is preferable. All ground floor constructions unless very large commercial floors will require some insulation to be included within the floor zone to comply with building regulation requirements.

At the turn of the 18th century when construction techniques moved from boarded floors installed directly on the ground to suspended timber floors over a ventilated chamber the innovation solved a significant problem. Push the cut insulation boards between the joists so they are flush with the underside of the floor boards.