Insulation Below A Groundbearing Slab – Design Guidance

Do not build load-bearing partitions off the slab, all partitions require their own foundations. Any DPM needs to be positioned on sand blinding (maximum allowable deflection +/- 5 mm over 3m length) to avoid puncturing; attach to the DPC around all sides. Any Radon Barrier needs to be laid underneath the slab and must include the whole building’s footprint.

Install edge insulation no less than 20mm thick around the floor’s perimeter to eliminate thermal bridging. Edge insulation depth should equal the insulation, slab and screed thicknesses combined.

Correctly laid Ballytherm insulation boards, will be positioned on top of the DPM/Radon barrier to protect them from ground moisture and from becoming contaminated. In lieu of a DPM and Radon barrier a correctly specified gas tight membrane may be substituted.

Between insulation boards and the slab it is recommended that a VCL such as polyethylene (1000 gauge) be placed to prevent condensation at the interface where they meet and to eliminate concrete penetration between the insulation boards.

a. 20mm min. edge insulation at perimeters  b. heating elements 

Floor Insulation

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