Warm Flat Roof - Vapor Barrier

14 May 2018
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United Kingdom
Hi, we are building a large flat roof and the following is what the engineer has specified:


For the vapor barrier (point c), there seems to be no such product available that I can find. The engineer is not helping.

Could you please suggest a suitable alternative that is effective in both its purpose and cost?

What is usually used for this step?
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Iko Easyseal
You can get self adhesive self healing vcl but it's expensive, a plastic sheet will if you are using pir then a DPM is fine.
If you are using eps or fiber batts you want a high performance VLC.

Thank you both for your replies. We are using PIR - Quinn Therm 150.

The self adhesive VCL is quite expensive. If we use that under the insulation, do we still need all 3 layers (venting layer, underlay, mineral cap sheet) above the insulation?
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What is the engineer doing specifying the roof finish and insulation etc :?:
Anyway, aren't there better modern flat roofing finishes nowadays than 3 layers of built up bituminous roofing felt :?::!:

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