False Ceiling Joists

[Adam Riley]

Hi,

So I have an extremely noisey neighbour above me and I cant afford to move so my only solution install a false ceiling with "sound" insulation. I have total of 175mm clearance to work with and my plan is to afix battens around the walls with coach bolts and then screw 45mm x 120mm joists from one side to the other. To stop any impact noises they'll be a 20mm gap between the original and false ceiling.

What I need to know is will 45mm x 120mm joists be able to hold the weight of plasterboard and insulation over a distance of 3300mm? They'll never be any other weight besides this and they'll be a total of 10 joists with a gap of 400mm between them .

 

[jacko555]

No. 2.4m @400mm

However, if you have to use 45x120 due to space, decrease the centers. Not sure what span 200 or 300 will give, the chart doesn't say. You get the gist though

 

[Deleted member 174758]

...will 45mm x 120mm joists be able to hold the weight of plasterboard and insulation over a distance of 3300mm? They'll never be any other weight besides this and they'll be a total of 10 joists with a gap of 400mm between them .

5 x 2s (120 x 45s) will probably cover 3.3 metres with a light load on 400mm centres if you go to C24 instead of C16 and add a load of strutting (say at 600mm centres) between them to stiffen the timbers, but a better, easier to install alternative might be to use resillient bars run at right angles to the existing joists (see here - there are other systems such as that by British Gypsum). Your plasterboards should be SoundBloc (acoustic) plasterboard and I'd recommend something like mineral wool batting (such as Rockwool RWA45) tightly fitted. Make sure that your plasterboard doesn't quite touch the walls at the perimeter, leaving a small gap which is sealed with an acoustic sealent such as Everbuild AC95. This is also useful to deal with gaps between the boards, too

A word of warning about soundblock boards - these weigh about 37kg for a 15mm thick 2400 x 1200mm board, so the hire of a board lifter to get them in place on the ceiling framework is highly advisable

 

[Dereekoo]

5 x 2s (120 x 45s) will probably cover 3.3 metres with a light load on 400mm centres if you go to C24 instead of C16 and add a load of strutting (say at 600mm centres) between them to stiffen the timbers, but a better, easier to install alternative might be to use resillient bars run at right angles to the existing joists (see herkge - there are other systems such as that by British Gypsum). Your plasterboards should be SoundBloc (acoustic) plasterboard and I'd recommend something like mineral wool batting (such as Rockwool RWA45) tightly fitted. Make sure that your plasterboard doesn't quite touch the walls at the perimeter, leaving a small gap which is sealed with an acoustic sealent such as Everbuild AC95. This is also iuseful to deal with gaps between the boards, too

A word of warning about soundblock boards - these weigh about 37kg for a 15mm thick 2400 x 1200mm board, so the hire of a board lifter to get them in place on the ceiling framework is highly advisable

Proposed joists are more than adequate to take proposed loads of less than 25kg/m² . Actual deflection 3mm with c24 or 4mm with c16, allowable deflection 9mm.
Strutting will add no value whatsoever except to add extra loads on the joists.
Ceiling joist table used above allows for concentrated point load of 90kg which is not relevent to your situation (i.e.no access)

 

[Dereekoo]

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[Deleted member 174758]

Proposed joists are more than adequate to take proposed loads of less than 25kg/m² . Actual deflection 3mm with c24 or 4mm with c16, allowable deflection 9mm.
Strutting will add no value whatsoever except to add extra loads on the joists.

No, but it will increase the stiffness of the ceiling which isn't always a bad idea.

Personally, as experience has taught me, I wouldn't do the job with timber as it reduces the amount of available sound proofing material you can get between the upper surface of the ceiling boards and the underside of the old ceiling. Presumably you can point us to a table for that, too

 

[jks7492]

Have a look at resilient bars, they can fix directly to the existing joists.
A lot cheaper and easier to install than a new timber ceiling...

 

[Dereekoo]

No, but it will increase the stiffness of the ceiling which isn't always a bad idea.

Personally, as experience has taught me, I wouldn't do the job with timber as it reduces the amount of available sound proofing material you can get between the upper surface of the ceiling boards and the underside of the old ceiling. Presumably you can point us to a table for that, too

Whilst the TRADA tables do advise strutting at edge supports and at various locations if the span exceeds 2.5m for floor joists nothing is advised for ceilings and why would they as ceilings have no upper or dynamic loadings on them that would provide twisting/sway forces to the top of the joist. Imagine a really long deep slender beam and standing on top of it, easy to see how it would want to bend over and flex to one side, hanging the load underneath it from a hook (say) wouldn't have the same effect.
Can't offer any advice on sound proofing as not in the scope of an SE.