400 or 450 centres in studwork

[bluebaron]

Hi Folks,

now I know the standard framing would be to use 400 centres to work with plasterboard.

But.. If I'm insulating between the studs and using 2400x1200 solid PIR then that would create a lot of wastage. (350mm between studs is 3.75 boards).

Insulation is expensive, plasterboard is cheap. So wouldn't it be better to use 450 centres (assuming no structural issues) with no/little insulation wastage?

Thoughts?

 

[sxturbo]

Use 450 but put extra battens in to stop the plasterboard from bouncing

 

[Notch7]

Hi Folks,

now I know the standard framing would be to use 400 centres to work with plasterboard.

But.. If I'm insulating between the studs and using 2400x1200 solid PIR then that would create a lot of wastage. (350mm between studs is 3.75 boards).

Insulation is expensive, plasterboard is cheap. So wouldn't it be better to use 450 centres (assuming no structural issues) with no/little insulation wastage?

Thoughts?

You can join celetex -tape it with foil tape to make up a full board.

or cut it the other way and have one join - you may need to cut around noggins anyway

 

[^woody^]

You space the timber to suit the boards you're fitting to them, not the insulation.

The offcuts of insulation can be used, not wasted.

 

[big-all]

are you using sheet material on the other side ??

 

[bluebaron]

Yes 9mm osb

 

[Deleted member 174758]

If your sheets are 8 x 4ft (2440 x 1220mm - most timber derived boards are this size) your joists should be on 16in centres (anout 406mm) to ensure the joints are carried by joists. On metric sheets such as PB and T&G chipboard, which are 2400mm dead long, your joists need to be on 400mm centres.

You space the timber to suit the boards you're fitting to them, not the insulation.

The offcuts of insulation can be used, not wasted.

 

[bluebaron]

Yep it’s a nightmare, do I space joist for the osb, plasterboard or insulation? can’t believe no ones sorted this mess out over the last few decades

I probably stick with 400.

Thanks everyone.

 

[big-all]

Yep it’s a nightmare, do I space joist for the osb, plasterboard or insulation? can’t believe no ones sorted this mess out over the last few decades

I probably stick with 400.

Thanks everyone.

100% better to get your brain in the 400/406mm space as everything and every body works to those sheet material timber sizes most tradesmen work to those standards so can work simply on autopilot without wasting time
my neighbour decided 450 centres on his summer house floor joist without consulting those doing 80% off the work it took about 40% longer and used about 20% more board as every board had to be cut at say 2250 with no where to use the offcut as its150 rather than 400 space where board down screw next board down and screw where as any offcut at 400 will fit

 

[Deleted member 174758]

Yep it’s a nightmare, do I space joist for the osb, plasterboard or insulation? can’t believe no ones sorted this mess out over the last few decades

I probably stick with 400.

At the risk of repeating myself and others - if you are boarding with a metric size sheet, e.g T&G chipboard (2400 x 600) or plasterboard (2400 x 1200) then you set joists at 400mm centres and if needs be cut Imperial-size plywood sheet, etc to size, whilst if you are boarding out for full sheets of non-T&G plywood or the like (8 x 4ft = 2440 x 1220) and no PB is going on the other side you board at 16in centres (approx. 406mm). Insulation is always cut to fit

Since you can cut plywood, etc and you can't stretch plasterboard, it really isn't that difficult to get to grips with the centres you joist at, nor is it so much of a mess if you or the architect plan your approach.

And in any case for specific purposes it is still possible to get 8 x 4ft (2440 x 1220mm) sheets of PB. Just not from Wickes or B&Q. I installed some foil-backed 8 x 4ft (2440 x 1220mm) PB on a small job a couple of weeks back. It was special order, but it is available. It's just for most jobs it isn't worth the hassle

 

[mrrusty]

there's always 1800 x 900 PB

 

[Deleted member 174758]

there's always 1800 x 900 PB

I only really used on repair/make good jobs - you'd almost never find it on a new build. In any case take a look at joist tables and see what centres they use for calculations - it isn't 450mm...

 

[mrrusty]

Only really used on repair/make good jobs - you'd never find it on a build. In any case take a look at joist tables and see what centres they use for calculations - it isn't 450mm...

I know - the question is why did they pick that size for a small sheet? why not 800x1600? anyone know?

 

[Deleted member 174758]

Because 1800 x 900 does work for the 600mm centres which are used on MF (metal framed) ceilings and some lightweight partition walls and for repair work, but most installers on new build specify 2400 or longer PB (e.g. 3000 or 3600mm for ceilings, or 2700s for walls - installed vertically to avoid the need for short infills at the top of the wall) simply because it installs faster with fewer joints which makes for a better finish as well as making the taper and jointer's job a lot quicker. It's well worth noting that 1800s can be carried round the corners in most stair wells as well as being transportable in even small passenger lifts - 2400s on the other hand can be a nightmare in already complete or near complete multi storey buildings as they never fit into lifts and won't go round corners without a lot of effort.

600mm joist centres are used with some composite trusses, but as they often get floored with something like T&G chipboard, T&G plywood or T&G OSB (all metric size sheets) it isn't an issue. Whilst that allows you to fix 1800 x 900 sheets to the undersides of the joists I still can't see anyone doing that when the widely available 2400 x 1200 sheets would fit just as well and be cheaper to install.

TBH any architect calling for Imperial sheets on top of say timber joists with metric PB below should also be specifying a secondary fixing system such as resillient bars (always a good idea for noise attenuation) to accommodate thise size mis match

 

[^woody^]

Yep it’s a nightmare, do I space joist for the osb, plasterboard or insulation? can’t believe no ones sorted this mess out over the last few decades

It was sorted out over a century ago, but yes there are still people that don't listen or understand