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How to achieve 3m Flat Roof height for my extension

Anonymous user 03/03/2024 - 3.45 PM

UPDATE: I have employed a professional to deal with it so NO HELP NEEDED, thanks very much ! I am planning to do extension - 6m wide 4m deep Bi-folding doors (rear and one side) would be 240cm tall and the internal ceiling height would be 260cm (including support to place RSJ beams on Bi-fold doors). A 30cm thick RSJ would then be placed, taking the total height to 290cm. There would then be 20cm-30cm thick timber placed on top of the steel beams to form the flat roof overhang/projection (where spot lights would be installed). This would take the height to 310cm - 320cmm tall.. Thing is we want a Flat roof (GRP) and not a pitched roof as we will have a roof lantern on top in the end. so really confused how to achieve a 3m height and have the overhang too? Catnic Lintels are out of question so how do we achieve a 3m height is proving to be a massive challenge...??? Our Roof height cannot exceed 3m as this is what has been approved by the BC… So, I am wondering if the overhang or the roof should be formed in a different way ?? please advise... Many Thanks in advance.

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3 Answers

GBS Design Services

Rating: 4.8 out of 5

Holywell

To answer your question about the overall height: the usual height for patio or bifold doors is 2100mm / 210cm - so I think your door height can be reduced. Secondly, the overhang of the roof (called the soffit depth) is achived by using the timber joists and allowing them to project beyond the wall plate by usually between 200mm to 300mm. You will also need to consult span tables for the correct size and timber grade for the joists. I suspect that you are trying to do this build without having detailed plans and I strongly recommend that you get a professional to draw up the plans and specifications and submit these to building control for approval. This would be money well spent in the long run!

Answered31 January 2023

Yorke Architecture Ltd

Rating: 4.9 out of 5

Doncaster

This is a detailed design issue, which is certainly solvable but surely the question should be directed at the designer you have employed to do this job rather than trying to get an answer for free, which comes with no design liability or adherence to CDM regs, etc. This needs looking at by a Chartered professional, paid for the expertise provided.

Answered31 January 2023

Cranleigh Planning and Architecture

Rating: 5 out of 5

Cranleigh

All good answers, but I think Building Control will ask for a 140mm thick Celotex to be sandwiched between 12mm OSB boarding which they term: A Warm Top. The Warm Top is a relatively new Bld. Reg. requirement for flat roof construction and sits on top of the roof rafters leaving the space between rafters free for aid flow. All this makes for a very deep roof construction. Hope this helps generally, but works against reducing height in your case.

Answered12 February 2023