Underfloor Heating in a Suspended Timber Floor Construction

Most upper floors have suspended timber joists and we use this technique for incorporating the underfloor heating pipes. Don't let anyone tell you that you can't have underfloor heating on upper floors. When architects or builders (or even some underfloor heating suppliers!) say that it can't be done it is usually because a method they have seen before is complicated or expensive. This technique is simple to install and provides good conduction from the underfloor heating pipes to the floor surface. An added bonus is that the sand/cement infill provides a significant reduction in sound transmission between floors. We always use this method when installing underfloor heating on a timber joisted floor.

 

Using this technique, the floor loading will be approximately 30 Kg per square meter at an infill depth of 25mm. Joist spacing should not be greater than 400mm. It is the responsibility of the architect, structural engineer, builder, or project manager to ensure that the joists are engineered to bear the load.

Sterling board or plywood provides a sub-base onto which the pipes are attached. Spacer battens are screwed through into the joists between the sub-floor and the final flooring material. These spacer battens must not be less than 25mm thick (recommended 30mm). Battens are included around the perimeter of the room. The ends of the battens are left clear by 100mm to allow the underfloor heating pipes to pass from one space to the next.

After the underfloor heating pipes have been laid, the space is infilled with a semi-dry sand/cement mix to the top of the battens to provide the thermal mass of the floor. This also provides some sound insulation between floors.

Rigid insulation must be used for timber joisted ground floors, fitted hard up against the underside of the sub-base. Mineral wool or glass fibre can be used for upper floors, but all through draughts must be eliminated.

Photo - Suspended timber floor with underfloor heating pipes installed

Close-up Photo - Suspended timber floor with underfloor heating pipes installed

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