Any advise comments appreciated regarding this project.
I have a single story flat roofed extension on the rear of my thatched roof cottage. I would like to remove the flat roof in exchange for a single pitched roof. However, I am unsure regarding the slope required, the thatch comes down to about one foot above the flat roof and the extension is about ten feet wide. I am hoping that I can use slates on the pitched roof.

Technically 17.5° is about as low as you can go in slate, I work your proposed roof out to be about 6-10° after you've raised it which my friend, is what is technically know as a flat roof not pitched!

Not 100% clear from your description exactly what you have tbh. Any chance of a piccy.

You wont get slates on that pitch! which would be regarded as a flat roof.

Can you raise the pitch by tying into the thatched roof?

Thanks for replies, I will try and get a pic' up but to be honest I am a techi hopeless case. I can't disturb the thatch so the only way I can get the 17.5% is by cutting the height of the external kitchen walls down. Its getting expensive now so perhaps I will leave flat roofed. Thanks again.

Thanks for replies, I will try and get a pic' up but to be honest I am a techi hopeless case. I can't disturb the thatch so the only way I can get the 17.5% is by cutting the height of the external kitchen walls down. Its getting expensive now so perhaps I will leave flat roofed. Thanks again.

You could (assuming you have deep pockets) build on a proper roof up to the height of the main roof and thus create a valley either side and then thatch the new roof. Simple really.