How do I calculate ceiling joist size and spacing ?

I'm installing an independent ceiling just below the existing one for sound insulation purposes, so the only load it will carry is an acoustic quilt above and plasterboard below. Assuming maximum span of 4m and plasterboard thickness of 25mm, what size joists do I use and at what spacing ? Is there a generic formula I can use if I vary the span and plasterboard thickness ?

Reply to
Señor Chris
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Done this a number of times before ( its my day job)..... We always use 6x2 at 600mm centres unless its a really short span of say less than 1.5m where you might get away with 4x2. Normally we fix a wall plate using frame fixings, then fix the cross members directly onto them. Leave about a 50mm gap between bottom of existing cieling and top of new joist and you should be fine. You don't want any movement in your secondary ceiling, you don't want to go to all the effort and then it still fails to pass regs, so we always tend to over spec.

Reply to
ch8rlie2000

minimum size will be 2x2, but since you want acoustic insulation the bigger the better, preferably much bigger than 2x2.

NT

Reply to
meow2222

Thanks for that. However, 6x2 doesn't leave me with much space for the acoustic quilt which is supposed to sit on top of the joists. Could I get away with 4x2 if I halve the centres ?

Reply to
Señor Chris

4x2" at 400mm centres sounds like it ought to do it.

You may find it helpful to have a play with the demo version of SuperBeam:

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a joist, and apply a uniform load based on how much weight you need to hang on it, and see how it performs.

Reply to
John Rumm

The formula is that for a timber beam. It requires some engineering knowledge to do from first principles but there are bound to be tables available on the internet or in a library. Basically if it is lightly loaded as it is - just quilt and plasterboard and its own self weight - you will not need a huge depth for a span of 4 m. I have used

225 (9") for a similar span that is a floor load that will be reasonably highly loaded so 150 mm sounds about right to me at 400 cc odd. Any less and your deflection would be too great and dont forget duration of load effects if you go too small Chris
Reply to
mail

CLS equiv may be an alternative to consider 148 x 38

B&Q had a great deal on this ... cheaper than local timber yard .... great for this type of job as it's all gauged and planed.

Reply to
Rick Hughes

put quilt between on netlon support

Reply to
Rick Hughes

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