Roof rafters for dormer conversion.

[David hackett]

Hi all, just looking for help with my dormer conversation. I’m installing new roof rafters 150x50 and sitting these on the load bearing eaves to which the original rafters from this to the wall plate are to remain but I have a couple of problems.

-replacing the whole rafter will make the roof higher than next doors if I birds-mouth this new 150x50 to the wall plate.

- how to I join the 70mm original rafter to the new 150mm rafter when this is being birds mouthed onto the load bearing eaves.

the photos might make more sense.

 

[Feck]

The drawings are not the greatest but my understanding is as follows.
Existing 70mm rafters stay in place. New 150 rafters glued & screwed to the side of existing rafters from ridge down to the new Eaves closure wall where they will be birdsmouthed. Top of new rafters will be level with tops of existing rafters and bottom of new rafters will be about 80mm below bottom of existing rafters. The new rafters don't appear to go all the way to the existing wallplate but could do if required with a seat cut to wallplate.
If in doubt ask your designer/engineer to clarify.