Hi can someone help,
i am ready to install roof on a simple lean to extension to my kitchen, I have decided to install 2X velox windows and have been advised from Building Control that i need to supply Calculations.
The origonal size of rafters are 6x2 which we have upgraded to 7x2 because the span (3.75)mtr with 400 spacing. we have been advised also to bolt 2 rafters together either side of the velox's for added strength. The Inspector advised us he still needs to see calcs. How do i get calcs without consulting a structural design engineer and paying through the roof?
Obtaining strucutral engineers calculations are your only real option forward. If the BCO has requested them he will need to see them. If you take all the information you have a local engineer, the amount of design seems quite minimal. I'd have thought this will cost in the region of Â£250 - Â£300 + VAT.
It all depends on the layout of the roof. If building control are happy to sign off the work if you omit the windows, you are ok. If you are only having rafters and no ceiling joists, building control may be concerned about lateral forces in the roof, effectively trying to push the external wall over.
My advice, speak to the building inspector, get him on your side, otherwise you'll be making an enemy you could do without. Most of them are really helpful if you ask their advice and get them involved.
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