Insulating a groundbearing floor below the slab brings the thermal mass of the slab within the insulation envelope, helping to maintain the building at an even temperature: the construction is suited to buildings which are continuously heated. This construction is compatible with masonry wall constructions and underfloor heating. Below slab insulation is well suited to new build and to refurbishment projects where a timber floor is to be replaced by a concrete floor.
The properties of Ballytherm Insulation match those required for this application: it is robust and moisture resistant, whilst its low thermal conductivity minimises the thickness of insulation within the floor construction.
The thickness of Ballytherm insulation required to meet regulations may be determined from table 4.
Design guidance
The Ballytherm boards should be laid on top of the DPM / Radon barrier to protect the boards from ground moisture and contaminants. The DPM should be laid on sand blinding (maximum permissible deflection +/- 5mm over 3m length) to prevent puncturing and joined to the DPC at all edges. Any Radon barrier should be laid beneath the slab and should extend across the whole footprint of the building. A correctly specified membrane can function as DPM and Radon barrier.
A VCL, such as 1000 gauge polyethylene, is recommended between the insulation and the slab to prevent condensation at the interface and to stop concrete penetrating between the insulation boards.
Edge insulation at least 20mm thick should be installed around the perimeter of the floor to eliminate thermal bridging at the edge of the slab
(see figures 2 & 4). The depth of the edge insulation should be equal to the combined thickness of the insulation, slab and screed.
Loadbearing partitions must not be built off the slab, but must have their own foundations.
Sitework Installation sequence
Blind the hardcore with sand to give a smooth surface.
Install the DPM / Radon barrier.
Cut Ballytherm boards to height and fit vertically around the perimeter of the floor.
Lay boards across the floor surface in broken bond. Butt boards tightly together and cut to fit neatly at edges and around penetrations.
Lay VCL: lap and seal all joints.
Pour and tamp slab.
Pour screed.
Points to watch
Test any embedded services before pouring the slab,
Protect Ballytherm boards from damage while the slab and screed are being poured: use barrow boards.
Protect the exposed edge of the Ballytherm boards when levelling the slab.
