I have to build a floor in a loft. At first this will provide a platform for some roof timber repairs to be carried out but ultimately it will be used for storage, not living space, so there are no formal BR requirements but, of course, I’d like it to be robust enough that it doesn’t all wind up in the bedroom below.
At present, there is a lath and plaster ceiling, with rather wimpy-looking ceiling joists, so not the most stable platform to work on. It’s in pretty good condition (as a ceiling, not a floor) so I’d like to keep it that way, which means installing joists clear of the ceiling timbers. This will, of course, create a void for a good depth of insulation.
So question 1: To work above the ceiling, I’m thinking of supporting it with boards on acro jacks, possibly moving these according to where I’m working as I go and putting some boards on the ceiling joists to spread the load (mostly me!). Does this sound like a sensible thing to do – ie any better suggestions?
One side of the space is an internal wall and the other side is a chimney breast with single-brick party walls in the recesses each side (these look pretty weak). Each end is the outside wall of the house running up about 60cm from the ceiling to the eaves of the roof. Since the shorter span (about 4m) is from the internal wall to the chimney breast/party wall, the joists for the new floor will run this way (ie parallel to the outside walls).
The plan is to use ledger boards (wall plates if you prefer) and joist hangers to mount 50 x 200mm (-ish) joists at 400mm centres. I know that socketing into the brick is favoured by some but that isn’t going to happen for many good reasons. To avoid going near the single-brick party wall, I’ll have to use trimmers across the (approx.) 1.8m recesses each side of the chimney breast, mounting joist hangers on these, so this is where the greatest loads will be: With 4 or 5 joists on each trimmer, their mountings will be carrying approaching 1/3 of the floor loading. The short ledger boards that these trimmers will mount on will, of course, run at 90 degrees to the others (ie along the returns of the chimney breast and along the outside walls).
So question 2: What’s the panel’s view on the best way to mount the ledger boards, particularly those that carry the greatest loads? I’m thinking of resin studs between each pair of joist positions (in the past I would have used expanding bolts but this is Victorian brick), but would a single large stud (M16) be better or worse than a couple of smaller ones (M12) and is there any benefit in supplementing these, with anything further (eg a pattern of multi-montis)? For the short ledger boards, I’m thinking four studs in a rectangle around each joist hanger. Using more mountings spreads the load, but over-perforating the boards would weaken them (though I suspect it would take a lot for this to be a big issue).
Lastly, to get decent access into the loft space (currently a 2x2’ hatch in a cupboard), I need to create a new doorway. The only way I can approach this is from the inside of the loft (due to obstructions I can’t practically re-position until the opening is formed). Normally, cutting a new opening would be best done using strongboys to support the triangle of brisk above until the lintel is installed but I’d hesitate to jack against the top of the ceiling and getting them through the hatch wouldn’t be easy.
So question 3: Instead of using strongboys, would a board (4x1 or so) fixed to each brick (multimonti into the brick centre) above the lintel do an adequate job of stopping everything moving while I get a lintel in? (A bit non-standard I know, but the best option I can think of in the circumstances!)