Roof rafters help

[David hackett]

Hi

I’m upgrading my roof rafters to accommodate a dormer conversion and I need to install 150x47 c24 timbers with a birdsmouth cut onto the wall plate. A third cut is 49.5 which the timber rafter will be 25mm to tall to the existing roof rafters of 75mm.

how do I loose this height difference so the roof stays the same height??

thanks

 

[Bonni]

So why 150mm timbers? Did you ask a structural engineer to spec 75mm timbers by doubling them up or/and with additional purlins etc..

 

[Terrywookfit]

So why 150mm timbers? Did you ask a structural engineer to spec 75mm timbers by doubling them up or/and with additional purlins etc..

Probably to accommodate the 100mm between insulation and ventilation.