My next door neighbour in a row of Edwardian terraced houses has begun a loft conversion. I can see RSJs being hauled up. He has planning for a dormer window and 3 roof lights (conservation area). No party wall notice. What chance he can do a loft conversion without putting an RSJ into the party wall?
He /might/ be putting the RSJs in parallel with the existing beams, front-to-back, then doing crosswise joists for flooring, but it's unlikely.
The roof conversion where the developer didn't get party wall consent, flooded the downstairs flat into uninhabitableness, and had to pay the downstairs neighbours ££££ for permission to dig trial pits to get load on the foundations past the BCO was one of the best episodes of Property Ladder.
Depends on which way the joists need to run, and what he has in the way of supporting walls to perch them on.
Can't see that even if he did need to fix to the party wall it is going to be much of an issue, a few heavy joist hangers and some rawl bolts. Not exactly in the same league as putting up shelves on it, but certainly closer to that than a "knocking out a chimney" class job.
Our conversion (don by Econoloft) a while ago was done "the wrong way round". They put a single steel front to back (the direction that is "tucked into the eaves" on our deteched house) and then wood joists out both ways to the end (gable) walls and new floor joists parallel to the steel. So, no steels whacked into the walls - it just rests on top of the front and back walls (on steel spreader plates).
The main problem is that the whole steel has to fit UNDER the new floor, so the height of the new floor is about 400mm above the first floor ceiling. Makes for a much reduced usable area up above, as the height of the new floor should have been about 250-260mm above the existing ceiling if they had stuck to the agreed plans.
Anyway the point is, as others have pointed out, you can run the steel or steels either way.
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