Hi Everybody,
I'm in the planning stages of upgrading an already converted loft (pre-regs, very little insulation etc) so that I can legally class it as a bedroom. I've paid the fee to Building Control and the surveyor has made their initial visit.
I'll be using SuperQuilt for the insulation (confirmed by the surveyor it complies with regs) and the existing stair case to the room is fine. If I can maintain the existing floor height (give or take), I will have sufficient headroom at the top of the stairs.
The existing floor is comprised of the original 75x75mm rafters, with additional 75x75mm spans between the lower purlins (I forget the proper name for these), and then chipboard flooring on top. The lower purlins are approx 130x50mm and span about 5.5m, built into the brick walls at either end.
My initial thoughts on the design can be seen below, using 75x170mm C24s (mostly) spanning (3.7m max, 450mm centres) from the roof plate and being sistered together over the central supporting internal brick wall. According to the span tables I have access to, the double member trimming joist (red arrow) will not comply with regs - assuming a flitch plate be an option here? Is there anything I need to consider by removing the lower purlins (I plan to mechanically attach the rafters to the new joists)?
I was discussing the above with the surveyor and she suggested I might be better reusing and adding to what's there already, which given what I know about the existing construction, has confused me a little. Ignoring the fact I'd never be able to get a 5.5m span of whatever into the room to sit alongside the existing lower purlins (with flitch plates), I'm under the impression that adding to existing rafters/joists etc is frowned upon?
Cheers
Tim
I'm in the planning stages of upgrading an already converted loft (pre-regs, very little insulation etc) so that I can legally class it as a bedroom. I've paid the fee to Building Control and the surveyor has made their initial visit.
I'll be using SuperQuilt for the insulation (confirmed by the surveyor it complies with regs) and the existing stair case to the room is fine. If I can maintain the existing floor height (give or take), I will have sufficient headroom at the top of the stairs.
The existing floor is comprised of the original 75x75mm rafters, with additional 75x75mm spans between the lower purlins (I forget the proper name for these), and then chipboard flooring on top. The lower purlins are approx 130x50mm and span about 5.5m, built into the brick walls at either end.
My initial thoughts on the design can be seen below, using 75x170mm C24s (mostly) spanning (3.7m max, 450mm centres) from the roof plate and being sistered together over the central supporting internal brick wall. According to the span tables I have access to, the double member trimming joist (red arrow) will not comply with regs - assuming a flitch plate be an option here? Is there anything I need to consider by removing the lower purlins (I plan to mechanically attach the rafters to the new joists)?
I was discussing the above with the surveyor and she suggested I might be better reusing and adding to what's there already, which given what I know about the existing construction, has confused me a little. Ignoring the fact I'd never be able to get a 5.5m span of whatever into the room to sit alongside the existing lower purlins (with flitch plates), I'm under the impression that adding to existing rafters/joists etc is frowned upon?
Cheers
Tim
