PIR board under floor slab - jointing tape required

[garyo]

Do I need to tape my boards together with foil tape, or will the fact that I'm placing a thin membrane over the top to prevent concrete getting between the cracks suffice?

Thanks!

 

[PrenticeBoyofDerry]

It's up to you Gary, the recommendation are tightly butted joints.

Installation Guidelines
Over slab installation guidelines
• Install a damp proof membrane over the top of, or below, the slab. The damp proof membrane must provide continuity
with the damp proof course in the surrounding walls.
• Level the surface of the slab; it should be smooth and free of projections.
• If required, use a thin layer of sand blinding on a rough, tamped slab to ensure that the insulation boards are
continuously supported.
• Use the Celotex Insulation Saw to cut and fit insulation upstand to floor perimeter, to meet a minimum R-value of
0.75m²K/W, (i.e. Celotex TB3020). The upstand depth should be equal to the sum of the slab insulation and the screed
thickness. The upstand thickness should not exceed the combined thickness of the wall plaster and the skirting.
• Lay the insulation boards directly onto the prepared slab with all joints tightly butted.
• Lay a polythene vapour control layer (VCL) over the insulation to minimise the risk of condensation forming at the
insulation/slab interface and to prevent liquid screed migration.
• Apply a sand/cement or self levelling screed over the VCL and Celotex insulation boards to a minimum thickness of
65mm.

 

[r896neo]

I usually fir an extra thinner dpm over the top and tape that. So as you suggest but make it something thick enough that a barrow,rake isn't going to tear through it dead easy.

 

[garyo]

Cheers chaps.

The BCO visited this afternoon. He seems to think I should put the DPM over the top of the insulation, rather than beneath. I know it's been a contentious subject on the forum in the past, and the plans I've submitted to LABC state that the DPM will be beneath the insulation.

I think I go along with him though - he's the one signing it off, after all.

Gary