Warm Pitched Roof = 2 membrane layers?

[Duncan62]

Or very good carpenters are saying I should have 2 methane layers on the roof. 

 

First as a house wrap.

Second draping between a counter batten, before the battens and tiles installed. 

 

Build up is: 

Insulation filled rafters

External 60mm wood fibre insulation

House wrap membrane

Counter batten

*Secondary membrane layer*

Batten

Tiles.

 

Is this standard practice on a warm fit design?

 

My thinking was a single membrane layer against the wood fibre?

[JohnMo]

15 hours ago, Duncan62 said:

should have 2 methane layers on the roof

Methane?

 

What do your drawings state?

 

Is you house wrap certified for roofing applications? 

 

Suspect the joiners are wrong. 

[Duncan62]

That should be membrane.

 

Yes certified: Rothoblaas Transpair Evo 160.

 

I did the drawings.

 

Roofer said single membrane. Will add butyl tape under each counter batten too. Belt and braces. 

 

Hopefully this sounds sensible?

[Iceverge]

Woodfiber boards don't need any membrane in some applications so the carpenters are over killing a little. 

 

Their understanding may be based on some older membrane types which demanded a ventilated layer at both sides as the weren't of sufficiently low Sd value. 

 

But for me in this situation:

 

Rafters with insulation 

Woodfiber.

Membrane (taped at joints) 

Battens

Counter battens 

Tiles.