Hi peelabee,
Your information appears to be too limited to give detailed opinions or advice about what you're doing.
Lots of questions arise that need to be answered first, for example; -
Firstly, the roof is the least of the issues that can arise, and I would raise the following queries in relation to the design of the existing works:
- How do you know the foundations are adequately sized to take a first floor extension?
- How do you know the walls are built adequately plumb and wide enough to take a first floor extension?
- Were the foundations designed to have a slip joint suitable for a single storey building or were they drilled and bolted enough to take a second storey without excessive settlement?
- If they were bolted, was the joint existing extension walling similarly secured?
- Was the ground supporting the furthest wall properly compacted, tamped and prepared to prevent settlement and rotation about the joint = otherwise you'll get cracks when you build?
- Was an engineer involved making these comments, was it a builder, is this your own opinion?
- Is the roof of the existing extension flat, and if so were timbers of the existing flat extension sized to be 1st floor joists - if not you'll need to replace them and/or add new properly sized ones?
Secondly, the design of the proposed works:
- Have you actually appointed your architect - if so he should be in a position to answer all your questions?
- Have you had him draw up plans for the extension over the ground floor rooms - whatever incarnation of spaces you desire?
- Have you had an engineer check the drawings and propose a competent structural solution?
- If you have these drawings have you gone out to minimum three builders for prices?
All that having been adequately answered, if you don't extend out the full way on the first floor, you will have to hold back a wall or two from the edge and these will probably need beam supports underneath, either in the walls or using a column or columns internally.
Unless you masterplanned this from the start to allow for an agreed first floor extension - and stick to what was agreed back then - it is unlikely that your existing ground floor has point supports for beams in exactly the right location to support the wall(s) position(s).
Anything other than a full perimeter extension will probably need to have this beam in place.
Even the full perimeter extension may require remedial work to the walling to help carry this load to ground perhaps involving provision of additional lateral support.
Ddon't just assume a ring beam will carry the load - ring beams with too much steel can lead to differential expansion and cracking.
Do get this all this structural work checked by an engineer.
New work needs to comply with Part L of the building regulations as well as the other eleven regulations.
Given your existing extensions, you may need planning permission.
Corner houses in particular need careful handling if the house isn't to look terrible with a blank gable.
It will need windows ti "lighten" the look of it and these will usually need planning permission.
There is a lot ot consier here, and a lot to do once you've considered it all.
The Askaboutmoney website isn't the place to undertake detail design.
You need to appoint a building professional and move forward.
ONQ.
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All advice on AAM is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent legal and building professionals should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.