To get the necessary headroom in the new porch you will probably have to strip back the existing roof edges and fit roof timbers which will sit on the existing wall plates. A deck is then fitted on these new timbers with the whatever construction you want above this. Since the edges of the new roof will connnect with a ventilated roof space I would suggest a cold roof construction.
Depending on sub-soil conditions you could probably get away with a cast-in-situ concrete beam under the front door. This sort of building work is ideally dealt with under the Building Notice method and you could discuss solutions with your local BI.
I had overlooked the fact that i could sit on the existing wall plate, and i will re look at that fact.
The plan originally was to fit wall plates to the two walls in between the bays and joist hanger the joists across from them ( about 2m max) with a warm roof for the flat top and as i understand it, then to strip back the hip roof tiles to say 1 metre and add a flat marine ply board on the rafters for the roofing felt to lay on.
Then replace the tiles back as was.
Never cosidered putting the joists on the existing wall plate :oops:
As regards to the front door, its all part of the planning / building regs for the rear extension, just thought i would kill two birds with one so to speak.
I will see what local authority has to say as you advise.
I hear what you say about the cold roof, but i have read that these are frowned on so to speak these days, any further views appreciated !
The reason for the warm roof is that i like the idea of an all in one board, a' la celotex td3116, but i am happy to be converted.
Thanks again for your input, its set me thinking agin
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