Installation of underfloor heating pipes between suspended timber joists

This technique requires that the floor joists be notched to allow the pipe to pass from one space to the next. You can end up with multiple notches in passageways, particularly near the manifold where all the pipes transit from the manifold to each of the rooms. It is essential that you check with your architect or a structural engineer as to the suitability of this technique to conform to building regulations.

This technique may be used where it is not possible to lay the pipes above the joists, e.g., where floor levels are fixed and cannot be altered. This method is more labour intensive but the end result is the same as the preferred ‘pipes above’ method. The joists are notched to allow the pipes to pass between the spaces. The space around the pipe is infilled with a dry sand/cement mix which provides the thermal mass needed to conduct the heat through the floor. Insulation should be a minimum 75mm rigid polystyrene.

Please note: If using this method you should check with your architect or structural engineer as to the suitability of this technique. We cannot accept responsibility for loss or damage to property due to the increased weight loading and stresses on the joists due to notching.

Insulation: Rigid insulation boards must be used for ground floors, recommended at least 75mm fitted hard up against the under side of the sub-base. Mineral wool or similar can be used for upper floors, but all through draughts between the joists must be eliminated.

Photo - Underfloor heating installed between the joists

Suspended timber floor construction diagram

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