Garage Conversion Roof query

Hi Everyone,

I'm planning on converting my garage in to a habitable room which I also plan to extend by 2.6 meters at the rear of the existing attached garage to maintain a small garage.

The original plan was to build a timber stud wall (insulated and with vapour barrier) to form a cavity in the garage which is currently single skin which seems to be a popular choice for garage conversions. The garage currently has a flat roof which would be changed to a pitched roof (hopefully vaulted inside).

My question is, would it be possible to have the rafters of the new roof resting on top of the newly installed timber stud work and if so, would I need a Structural engineer to make sure there isn't too much weight on the timber stud wall? Or;

Would it be better to dig foundations inside the garage and build a new block inner skin and tie it in to the existing garage wall? If this is a better way of doing it, can I use a narrow foundation (but still go down a meter) so that is doesn't impact on the garage wall that would remain in situ?
I hope this makes sense and any information would be greatly appreciated.

Thanks in advance
Jim

If you put the roof on a new inner leaf, timber or masonry, then that leaf should be on a suitable foundation.

So put a wallplate and the rafters on the external wall.

Perfect, Thanks Woody I've been trawling the internet for the answer so that's much appreciated!