Warm Flat Roof - Vapor Barrier

[josh1000]

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?

 

[^woody^]

Iko Easyseal

 

[tomfe]

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.
https://www.roofingsuperstore.co.uk...MI7aem2d-e4wIVVON3Ch1TGgZ-EAQYASABEgI3ifD_BwE

 

[josh1000]

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.
https://www.roofingsuperstore.co.uk...MI7aem2d-e4wIVVON3Ch1TGgZ-EAQYASABEgI3ifD_BwE

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?

 

[Leofric]

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