Sound Proofing in Timber joists

eagerbeaver1

doing a new house build in the country and contemplating whether to use concrete pre-cast 1st floor or go with timber joists - the latter being a significantly cheaper option but pre-cast offering must better sound insulation qualities. Already got a quote for ~3k pre-cast but that doesn't include the top finished screed + mesh and suspended ceiling - will be 5k before I'm finished - will put in a lot of timber joists for that.! There are sound insulation methods out there for timber joists but not sure how well they really work - place rockwool between joists + place acoustic tape on top of 2" joist + lay down plywood and then roll an acoustic material out over the ply before laying down your finished floor (timber / carpet etc) ..... but who has it done and does it work well ?

bb12

would be interested in hearing people's experience of this also. i've no choice but to opt for timber joist. initally my builders quote came back without anything between them at all, but when i queried him on it he offered to put 150mm of rockwool in between. don't know what effect it will have on sound issues though.

KingPuck

If going for timber joists consider using 9x3s rather than 9x2s to take some of the spring out of the floor. Alternatively use 9x2s and double up every third joist.

Also take care to use as short a screw as you can to get a proper fixing. Sound/ vibration travels through the screws.

If it's a 2 storey it wouldn't be too expensive, however if it's a dormer you'll have some heap of expensive floor behind the knee walls.

RKQ

eagerbeaver1 wrote: »

There are sound insulation methods out there for timber joists but not sure how well they really work - place rockwool between joists + place acoustic tape on top of 2" joist + lay down plywood and then roll an acoustic material out over the ply before laying down your finished floor (timber / carpet etc) ..... but who has it done and does it work well ?

I would also double slab the ceiling. Look at plasterslab manufacturers for details of their accoustic 19mm boards that can be fitted between joist on metal tophats.
Soundproofing is improved by adding layers and preventing vibration. Sound does travel along screws.

From experience I can say that double slabbing the ceiling gives better sound insulating performance.

martin46585

with relation to my own build the pre cast route is by far the better option.
the price quote will be supply and fitted which allows trades straight back in, secondly pre cast allows you to build your upstair wall where you like with solid blocks, which adds to the soundproofing with toilet flushes & showers, no notching or boring joists for pipes /cables, and lastly the fire rating is again way better.
so perhap weight up the difference in the two, the timber floor will be more labour and with items like gysum resilient bars,insulation, soundblock plasterboard costs will soon mount up.
just a point to finish on the precast does need 9" walls to meet on and may also need some added rsj's

sinnerboy

Either construction method will perform poorly if all services penetrations are not completely sealed . You know when the car window is down the traffic noise remains right up the point when even the tiniest gap remains - thats sound penetration for you. Cables , water pipes ( heating , DHW , drainage ) all need to pass between stories . Make sure all are sealed before plastering over .

eagerbeaver1

thanks for de tips lads - spoke with a builder earlier and he's sometimes used RSJ's across the widest span and then ran joists at right angles into them thereby shortenning the joist spans .... basically making the floor structure more solid. going to get some pricing done both ways anyway and will see how it work out but if there's only a grand or two in it then the pre-cast sounds a better option and less labor intensive afterwards - no tapes, acoustic membranes etc