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Sister joists for loft conversion

Postby andy654321 » Thu Mar 31, 2011 9:22 am


I am going to convert my loft space into a bedroom and bathroom. It currently has 6x2" floor beams with 16" centers for a total span of 17feet. I would like to know if I sister these joists to some 10x2" will it be strong enougth for a 17feet span and do i need to use joist hangers on the ends of the new 10x2?

Thanks for any advice info

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Postby chris_on_tour2002 » Fri Apr 01, 2011 11:01 pm

this is notifiable work - Building Control need to approve and sign off the work, both on principle and on completion to ensure that it meets not only with structural regs but also fire regs as well. in order to get BC approval you will need to consult a structural engineer anyway - they will tell you what will need to be done.

a proper staircase will need to be put in for fire safety reasons unless evacuation in an emergency can be done safely from a window in the loft space.

in some circumstances you can get away with 6x2" if steel beams are inserted though it can be a tricky job getting them in.

many people carry out loft conversions without the necessary approval - all well and good but it will not add value to your home as you can only class it as a loft space, not an extra bedroom. not to mention what happens if there is a fire and inadequate provision for evactuation has been made.

the advice has to be to get in a structural engineer and get BC involved.
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