Best way to cut roof insulation around these little dormers...?

[Dannyboyski]

We're having a new roof on our renovation.

building control are onboard etc. Replacement roof will have a u value of 0.16.

I'm using superfoil sf40BB which is insulation foil and breather membrane in one.

this should be a simple job but for my little dormers.

Ive laid a couple of sheets on the roof with clamps for now, while I decide whether its best to cut or fold the bottom sheet where it goes up the little dormers...

any advice please....?

looks like a straight cut in the membrane at the top of each dormer then put a fill piece over the top of each dormer ridge.

Many thanks

Dan

 

[^woody^]

Is there a manufacturer's guide for cutting and sealing? I would suspect that it needs to be cut centrally to the valley, and then both pieces sealed with tape on both sides of the insulation. Alternatively cut a little longer than the centre line and lap the insulation on a central batten.

Running insulation in this way over the valley means that the valley boards themselves need to be raised (replicated) above the insulation.

 

[datarebal]

cut tight at the top no gaps, tape all cut edges.tape all joins then a strip of underlay to weather the ridge as you suggest. avoid double thickness of the insulation content it will cause slight humps in the battens.
A problem if you are having a slate roof

 

[Dannyboyski]

it will cause slight humps in the battens.
A problem if you are having a slate roof

Yes I suspected this. It is being slated.