Foil membrane on a new mono pitch roof

[DIYWell]

We're gonna have a little extension built on the north side of our house to create a bigger kitchen.

The roof will be mono pitched with the line of the ceiling running parallel to it to create a pitched ceiling and give the feeling that the room is bigger than it really is. The pitch is 15 degrees.

The architect has specified tiles, battens, Proctor Roofshield underlay, sarking boards then rafters. I'm wondering if there's room in the sandwich to either change the Roofshield for a breathable foil underlay, or put a foil layer in elsewhere just to up the insulation.

Has anyone here has experience of this type of sandwich before and can give me some pointers?

 

[freddiemercurystwin]

Get your architect to advise that what he's paid for.

 

[SurreyRoofingEstimator]

Agree with Architect comment (would be nice if they did their job properly once in a while)

There is a product available which combines a breathable underlay and multifoil insulation from a company called Webdynamix, the product is TLX (Thinsulex as was) Gold, this has been suggested to us by a local council where we have a similar situatuion (though on a refurb project). It costs around £10 per square metre, not too cheap but of course you do lose the cost of the underlay

 

[DIYWell]

Thanks. Always good to be able to state a product to an architect.