Loft conversion joist detail

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Hi,
I am converting my loft and i have a question regarding how best to fix the new floor joists.
We are lucky with the construction of the house; the new floor joists can run from the current inner wall plate under the eaves to the central spine wall.
My question is how best to fix them.

option 1 - lie the joists as close to the current rafter as possible and fix to the side of them.

option 2 - lie the new joists in between the rafters and fix the overlapped ends in the middle.

Both options have the downside of only one end being fixed; but i am unsure what is best.

  • They will rest on 18mm packers so that they do not touch the ceiling below.
  • A dwarf wall will be built off them around 1m from the eaves in place of a purlin.
  • Current rafters and ceiling joists have plenty of twists and bends

BC are happy with the general design and the engineer has specced the joists as 47*225.
Thanks for your help.
james

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I would suggest 2 things; a structural engineer and building regulations.
 
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Dependant on what your structural engineer specifies an option would be to fit a timber of 47 X 225 at right angles to the existing rafters, either sat into the outer walls if possible or on brackets or hangers and notched to sit in between them providing a fixing point for the ends of the new timbers and it would also spread the load over the rest of the surface.
 

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