Loft room

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Can anyone advise what are the key things to look for when converting an existing loft room to building regs, ie thickness of floor joists, board type, sidewall insulation requirements, purlin supports?
What is required to add a dormer or velux?
Is a stairway required? I'm not looking to extend but make a useable space and convert the existing space to building regs, and possibly add a stairway ( though there may not be enough room.
Thanks.
 
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You look at head height, and stair location. Everything else is part of the conversion, but those two are the most onerous and expensive to achieve if not already available.
 
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Sorry don't think made I made it clear. There is a boarded floor space and plasterboard sides there at the moment however joists don't look that thick and it doesn't already have BR. There is good head height. 2m id stay. Staircase could be added to the centre in the hall. Does it need staircase to get building regs on putting a window in? Would be prepared to add a staircase, but don't want to gave to redo the floor%sides, it's a bit g area. What's size joists are required? Or maybe steels?
 
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It's not a grey area at all, if you want to ever be able to sell the property with an additional bedroom it will need building regs and so will need a stair. And 2m won't be enough, the existing floor joists will be inadequate so the floor will be thicker, insulation at roof level can easily add 100mm, budget about £25-30k for a dormer conversion. A steel beam each side with new joists spanning between is pretty typical, a steel at the ridge too for a dormer, though these could be timber. Your questions are too vague/open ended atm to give any better advice.
 
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Are you saying you can't get BR if the head height is less than 2m?
 
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No, oddly there is no minimum ceiling height in the regs that is except for above a stair, which is 2m, or 1.9m depending on where its measured. But as mentioned if you only have 2m from existing floor to the underside of the ridge, even wih some clever design and ballbreaking building you'll only end up with about 1.8.
 
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OK thanks that clarifies the height then. Is there a minimum size for floor joists? Or do bthey just need to be suitable for tgtghe span?
Does it have to be insulated to 100mm to get BR too?
 
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OK thanks that clarifies the height then. Is there a minimum size for floor joists? Or do bthey just need to be suitable for tgtghe span?
Does it have to be insulated to 100mm to get BR too?
About 150mm of Celotex. That would be 100mm between the rafters with a further 50mm across (beneath) them. If your rafters are not deep enough to accommodate 100mm of Celotex between plus a 50mm air gap then you will need to add thickening battens to the rafters.

When you factor in deeper joists, floor deck, additional insulation and plasterboard beneath the rafters, then you are looking at a considerable reduction in the amount of available living space remaining between. As Woody says, it is where the stairs enter the loft that is critical.

We are fitting 225mm deep joists over a 4m (clear) span in the cavernous loft we are converting at present
 
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