Gluing and screwing on top of existing joists in the loft. Does shrinkage cause problems?

The CLS stuff they sell for studding etc is kiln dried IIRC. It's not going to shrink much, especially if the loft is unheated

Use plywood?

How do you mean? built up in layers to add another 4 inches?

No -I mean use plywood which should not shrink.

Sounds as though the OP is insulating the rafters, so presumably there is no point in raising the floor level by 4". Ply would be ideal if, for some reason, the floor needs strengthening

That would be good but I want the floor space to be available from eaves to eaves, no walls.

I think CLS timber is the tip that I have been looking for. Just need to see if I can find it in 5 metre lengths.

Could you get 5 metres into your loft?

I think you want KD. CLS is KD, but also meets other unnecessary specs. Practically speaking it neednt necessarily be C16 rated, as you already have enough sound wood in place.

It'll be fun getting 5m thru the hatch :)

NT

Yes you are right. I was in Selco today and everything seems to be kiln dried already. Seems I was worrying needlessly. I'll probably take a few tiles off the roof somewhere to get them in.

Thanks all.

top will meet that need? I am a bit surprised. I thought one normally laid a full sized joist next to the old one. Have building control approved the method?

This is known as "sistering" and my understanding is that if the ceiling joists are 4x2 and a floor joist in the same situation would require an 8x2 then the BCO would ask for an 8x2 to be sistered with the existing 4x2.

I'm interested to be told different as I'm still vacillating over whether to do a proper job or just use the space for storage.

AJH

Or above a window cut a hole in the ceiling and slide them in through window and ceiling and patch ceiling afterwards.