"Inverted" dormer detail

[mittuck]

I am working on a relatively large rear lean-to extension.

The roof clashes with two windows above (even at the very low angle I have the roof) and, thus, I need to create, what I can only describe as an inverted dormer, so as I can meet wall min. 150mm below this windows and flash my roof. (example picture attached)

My problem is I don't know which roof system to use so as I can marry it with my pitched roof, which is an unventilated, between & below rafters insulation construction (image attached).

Any suggestions would be welcome as I am unable to get through to Kingspan for their suggestions.

Many thanks
Michael
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[^woody^]

Like this?

Untitled

• ^woody^
• 20 Jan 2012
• 5

 

[hardmetalking]

A warmfast zinc roof would be appropriate and the same material can be used for the whole roof including the inverted dormer and flashings. Even the gutters and down pipes can be fitted using matching zinc.

 

[noseall]

So, what you propose is a shallow pitch vaulted roof with insulation between and below the rafters?

If so, why do you state 'unvented'? Surely you can use breathable membrane or am i barking up the wrong un?

The flat parts in Woodplanks image would typically be insulated with foam board insulation on top of the timber deck (horizontal) and between the uprights of the vertical bit with additional insulation across the uprights internally.