OSB for loft boarding

[The Night Tripper]

Hi All I'm planning to board up the loft properly this winter - putting down 4x2s at right-angles to the current joists and filling in between with a new layer of insulation (Celotex/Kingspan or the normal roll insulation stuff), then boarding over the result.

I'm unimpressed with the T&G chipboard panels the sheds sell for this purpose and was thinking of using OSB, probably cut into eg. 4ft x 2ft panels for easy of fitting.

Any thoughts on the right thickness of OSB to use? 18mm seems a whisker OTT, but I don't think I would trust 11mm. I guess I'm thinking of around 400mm 'joist' spacing.

Thanks J^n

[Stuart Noble]

What don't you like about the chipboard panels? They're designed for the job.

[PeterC]

Been looking at this recently and same feeling re. T&G chipboard - also want to be able to lift individual sheets for access to various things.

Wickes' chipboard and OSB seems good, not just cheap water-soluble stuff.

For OSB, have a look at

stock: OSB/3 Load-bearing applications in humid conditions

Plywood - exterior/WBP is an option, although expensive. 18mm would do, be heavy and expensive. 12mm might be too thin, but I've tried an offcut of

12mm across 3 joists; it does flex a bit but not badly and in wider pieces and with a few screws in might be OK.

In another thread, whitewood plain (non-T&G) floorboards were mentioned (from Jewson, IIRC). That would be an easy, modular, way od doing the job. The wood would have to be treated and normalised (but even OSB needs normalising).

[NT]

putting down 4x2s

google sagulator, it'll tell you how much flex you'll get with the various flooring options.

I prefer non-T&G chip for easy access.

NT

[geraldthehamster]

putting down 4x2s

For what it's worth, if you can get to the ends of the existing joists (4x2?) where they sit on the wall plate, and glue and screw your new

4x2s on top of them for their full length, you will make a much stronger floor than by just laying 4x2 across the joists. Effectively you would be creating new 8x2 joists, which is almost up to current Building Regs for a proper floor.

My bungalow is a good illustration of this principle. The chap who built it used 7x2 joists for half the first floor, and 4x2 for the other half (don't ask me why; much of the material was scavenged so it's probably what he could get hold of). When he had a family he made some rooms up there. To have a level floor he laid 3x2 over the 4x2 on that side of the house. So - one half of the floor was on 7x2, and the other on what you propose. The 7x2 side was rock solid, and the 4x2 + crosswise 3x2 tended to move up and down, which not only felt unstable but produced cracks between the plasterboards in the ceiling below (I've since removed the overlayed 3x2, and installed new 7x2 between the original 4x2).

You're not converting your loft to habitable space, but it's worth considering making the floor as strong as you can, so you have the option of storing heavy stuff up there without worrying about the loading.

Cheers Richard

[Dave Liquorice]

The price? At least that is the impression I have compared to buying similar chipboard in 8x4 sheets. I guess they are fine if their dimensions also happen to coincide with the joist spacing. Personally I'd rather buy enough sheet and cut to fit the spacing I have rather than faff about trying to fit silly little panels to the spacing and still ending up cutting or fitting noggins etc.

[auctions]

putting down 4x2s

Saw this when I was in BnQ the other day - don't know if it's any good, and I've not worked out the relative costs, but would be an easier solution possibly:

[Stuart Noble]

Depends whether you regard t&g as beneficial. If the joists aren't level, it at least makes the joints flat. The 8x2 t&g sheets are handy if you have the space to handle them in the loft. I always end up laying the small panels across the joists anyway, but I've been lucky with the spacings, so the wastage wasn't too serious.

[fred]

In article , The Night Tripper writes

Have you considered laying Celotex directly on the old joists and boarding over without the additional cross joists? Celotex is pretty good in compression and as long as it's not pianos that you're storing up there, then it could be the way to go. Avoid having Celotex sheet joins on the joists, the edges would be more likely to crumble.

11/12mm would prob be a match for this sort of light, load spreading design.

[The Night Tripper]

Hi Stuart

IMO they are designed for doing the job to the very lowest level of acceptability and with low cost as the maind driver.

The ones I have encountered are very crumbly near the T&G edges and do not take screws well. They are also on the thin side and the sag they demonstrate when standing on do not give me much confidence. To me they are an example of something designed by the 'sheds' to appeal to those with little knowledge of what else might be available but for whom convenience of purchasing and packaging are major criteria

(I don't mean you by this, Stuart!)

J^n

[The Night Tripper]

I would like to do this, and can get to the ends of the existing joists - but I can't get new timber the same length as the joists into the loft! I will have to cut them down into sections approx 3m long, which presumably would spoil most of the effect you mention.

I suppose one could find a way of re-joining the timber once up there - ideas?

Cheers J^n

[The Night Tripper]

Hi Peter

Thanks for the links etc.

Yes, I will price up floorboarding to check the relative costs. I've a feeling 4ft by 2ft panels will be easier to lay though.

by 'normalising' I assume you mean leaving in the appropriate atmosphere for a period of time?

Thanks J^n

[Tim W]

The Night Tripper wibbled on Thursday 08 October 2009 22:55

I'll add that all the ones I've been ripping up (later to bin) are filling my ceiling voids with not insignificant amounts of sawdust aka mouse fodder and fire tinder. I hate them. Brand new ones are OK (I bought one pack from Wickes just to give myself some short term boarding in the roof corners), but IME they really don't age well... Planks of wood or ply are way better.

[Stuart Noble]

Well, that's me alright! It's a loft, not a living room :-) They've been absolutely fine in my loft for the last 15 years or so, and I've had sawbenches and all sorts of heavy stuff up there. I've never seen the need to screw them to the joists at all. As long as the edges are fixed, how are they ever going to move?

[PeterC]

I'd like to know the results, please. I did look at Jewsons' site but couldn't see any and I'm too far from doing the job to ring atm.

I'd prefer panels but can't get them up there on my own (8x4 will just about go but need angling and steering carefully), so floorboards, in spite of the need to treat them, would be manageable.

Yes. I was surprised tha OSB needed this as it has a lot of synthetic content. Important for floorboards as there a many gaps (especially T&G). In a loft, of course, the conditions are far more variable than in a bedroom, so what is 'normal'?

[NT]

why would you need to treat them?

NT

[PeterC]

Untreated wood in a loft? I had that in a brick shed (similar conditions) and got woodworm. OSB, WBP and chipboard aren't so palatable to the little blighters.

[The Night Tripper]

Hi Fred

I have thought about this, but I don't like the idea of doing it with

*small* (4ft x 2ft) panels. It feels like it be a lot of work faffing around with lining the panels properly over the joists, with the Celotex in the way. I also have the picture of all the panels giving way to different degrees, with the whole thing ending up looking like badly laid paving slabs, if you see what I mean... (OK, i know, it's only a loft...)

I'm also considering doing only (say) half of the loft in one guy, but buying all the materials. if I cut down celotex to suit then I can stack it vertically for now.

But I'm happy to be convinced that this is a better way to do it than any I've come up with ...

[The Night Tripper]

Hi Peter

A few things I've found out:

eBay do reclaimed floorboards (see a thread from a month or so ago) but they tend to be of 'architectural interest' and be around £20/sqm. You could probably find some for £15 per sqm, not sure about delivery.

Wickes PTG softwood flooring - packs of 5 (18mm x 121mm x 3m) is £22.40, ~ £13.25 per sq. meter.

11mm OSB (2440 x 607 x 11mm) is £8.98, £6.07 per sqm 18mm OSB3 T&G Roof Deck (2440 x 1200 x 18mm) is £19.95, £6.81 per sqm. T&G on the long sides.

Loft Panels (ie. what I don't like) Pack of 3 (1220 x 320 x 18mm), £4.87, £4.17 per SQM.

FWIW I played with the sagulator a bit. Since the gradings for particle board are not ones I'm familiar with, nor know the UK equivalents of, this is all a bit handwaving. And I put fairly arbitary figures in for shelf load and span etc. However, for purposes of comparison only:

(all 18mm thickness) particle board sag: min 0.9mm, max 1.5mm MDF: similar to particle board OSB: min 0.30mm, max 0.55mm Various types of pine: < 0.3mm

The OSB is still looking good to me -I'm going to try to cost some 15mm OSB panels.

HTH J^n

[PeterC]

Intersting figures, thank you.

I'd be very interested in 15mm OSB as I've seen only 11/12mm and 18mm.

Trying an off-cut of 12mm WBP indicated significant flexure; this was across 2 joists and only about 60cm wide. Longer, wider and screwed down would help stiffen it a bit.