Screed Floor Structure

This floor construction consists of 65-70mm screed on extruded polystyrene insulation over base slab on DPM, sand and compacted hardcore. This type of floor construction gives excellent results with UFH and is more responsive than the slab floor.

Screeded floors are commonly used in domestic applications; other buildings that would benefit are schools, hospitals, offices and nursing homes. The response time with this floor structure is more suited to buildings that are permanently occupied and require a day/night set back system.

Slab Floor Structure

This floor construction consists of 100 to 125mm concrete incorporating builders mesh (normally A142) with UFH pipes tied to the mesh, over extruded polystyrene insulation, on DPM, sand and compacted hardcore. Insulation is also required around the perimeter of the slab. Due to the large mass of the concrete, this type of floor structure will have a longer initial heat up time but benefits from having more thermal inertia.

Solid slab floors would normally be used in commercial buildings with high floor loads, such as warehouses and garages, but can also be used in domestic situations. The build up of this type of floor provides a large amount of thermal mass; subsequently the floor structure will be slower to respond to different heat.

Timber Joist Floor Structure

Timber joist floors have no thermal mass, for best results with UFH a small amount (25mm thick) of weak sand and cement can be laid between the battens to surround the UFH pipes. The sand and cement should be up flush with the top of the battens to ensure good contact with the underside of the flooring panels. It is essential that a rigid insulation board (not glass wool) be used to insulate hard up the underside of the plywood (see diagram). Using this method the floor is raised by 34mm higher than it would have normally been and adds approximately 25kg/m² in weight.

Timber joist floors, either ground or intermediate, can be addressed in different ways. A timber floor has no thermal mass and some adapting is required to the structure to enable floor heating to be installed and operate successfully.

The best results are obtained by fixing the pipes between battens and infilling with a sand cement mix, the floor panels are then fixed to the battens. This method can be used either on top of the joists, or by fitting battens between the joists it can be lowered so that the floor panels are still fitted onto the joists with no increase in floor structure height.

Another method is to use profiled metal plates as a means of spreading the heat energy under the floor panels, this method does not impose a weight penalty but the energy output is lower than the batten and screed method.