OSB for loft boarding

In article , The Night Tripper writes

I can understand you reservations.

It helps if you have some Celotex/Kingspan lying around as you can see how tough it is in compression.

As a test, I just took a spare small piece of 'tex and placed it over a couple of 18mm wide battens before adding a small board on top and jumping up and down on it. It did creak and deform by about 0.5mm at the battens so it was at the limit but that was 80kg+ over only 50cm2 of narrow contact on the battens. Scale that up to 50mm joists at say 500mm centres and the test was equiv to 3200kg/m2 so it suggests that a few

100Kg/m2 would be well within safe limits.

As to alignment, if you lay the 'tex and mark the joist positions on the top foil surface with a marker pen then it is relatively easy to keep track of their positions. If you were then to align the OSB with the edges within 25mm of the joist position then I would say that was safe enough. I wouldn't even screw the boards down (unless it proved necessary) but would float it and tape the seams with good quality duct tape. Just keep the 'tex joints away from the joists.

How does that sound? It seems a lot less work that cross joisting.

Reply to
fred
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Hi Fred

Thanks for this; I'm aware that my reservations are in part due to lack of real experience with Celotex. I've tried to press my thumb into a sheet in Wickes; that's about all ;-/

What thickness of Celotex are we talking about here anyway?

That all sounds reasonable, and as you say much less work than cross joisting. I'm still not too sure about the relative staggering of the Celotex and OSB panels though - especially if they're both of a similar size to go through the loft hatch. I will do a few layout doodles and see what I can come up with. I would quite like to be persuaded that this is the way to go ;-).

Cheers J^n

Reply to
The Night Tripper

In article , The Night Tripper writes

The sample I used for the crush test was an offcut of 25mm but I think it would be the same result for thicker stuff. PIR foams are close to twice as effective as fibreglass so a 50mm sheet plus say 4" of fibreglass that you may already have between your existing joists would be about right.

Perhaps a bit more difficult with the short sheets but maybe a staggered arrangement will work somehow, get sketchin :-!

Forgot to say, there are places you can buy Celotex and Kingspan in light seconds grades at much reduced prices, google for Celotex/Kingspan seconds. Here's a couple from my bookmarks, don't know if they're any good:

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Reply to
fred

Hi Fred

Hmm. I had 50 or 100mm in my head, that's maybe one reason for my concerns. I haven't done the relevant U-calculations, will have to get around to that.

If 50mm Celotex would do thermally (I have some decrepit fibreglass between the joists at the moment and already have some new rolls up in the loft ready to lay prior to anything else) then I'd be reasonably happy with this construction.

are based in Wales. Seconds seem to be closer to be (Tunbridge Wells - I'm near Brighton) but i'll check both of them out.

Cheers J^n

Reply to
The Night Tripper

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