Joists - built into wall or set on hangers - Building Regs?

[Steve_W]

Afternoon all,

Just a quick question about Building Regs since I can't get through to our council at the mo.

Is there a rule on first floor joists regarding it no longer being ok to build them into the supporting walls? I.e. are joist hangers the only allowable solution now?

Also, if the joists for two walls are run onto a supporting wall between those rooms, by how much must the joist sit on or overlap the top of the wall (if that's allowed)?

Ta,
Steve

[mackg]

I'm not 100% sure but I think the joists have to go into hangers for some reason, I think it may be because of heat loss round the joists if they shrink! As for sitting on load bearing walls they have to sit on the full width of the wall and can fly through by a couple of 000mm but no more

[Tom_C76]

Assuming solid joists, you can build them in still, but you have to run round all 4 sides with mastic to seal against air leaks.

[mrmaggit]

Not strictly true, the air test changed since this was brought out, and if the plasterboard is sealed around the edges, there is no need to have joist seals, as the test is for the room, not the space between floors.

So says the man who has quite a few joist seals in stock that he is going to struggle to sell.

You live and learn.

[Tom_C76]

But if you seal at the board edges you'd then have to seal every opening in the boards if you want to be sure of passing. Could be a load of grief if you have a thing for downlighters...

[Steve_W]

Hmm - hadn't thought about airtightness.

Luckily, since we're only putting up an extension, I don't think the test applies to us?

So, as long as I seal round the joist ends, I should still be ok to build the joist into the wall?

Thanks,
Steve