50mm Rockwool in cavity wall not 100mm

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Hi lads
Can I use 50mm or 75mm in cavity walling and not use the 100mm, its a small music room extension and trying to cut back in costs? 100mm fully fills the cavity I know but would it be k to not totally fill it.
Thanks
S
 
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The difference in price is very marginal considering it's your house.
Invest a little more and you won't regret it.
Otherwise you could have a 50mm cavity and the bricklayer will curse you for a good time.
 
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The difference in price is very marginal considering it's your house.
Invest a little more and you won't regret it.
Otherwise you could have a 50mm cavity and the bricklayer will curse you for a good time.

Thanks, t works out about £12 more perpack for 100mm and then there is less slabs too for coverage, is there anything else I can use cheaper than rockwool at 100mm for the cavity. I intend to also put 50mm acoustic sound slabs on the inside of the build.
 
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See if you can get some 75mm Dritherm 32 from B&Q - cheapest you will get and it's performance is not far off standard 100mm batts, however it won't quite meet the regs with standard brick/block construction (but may if your acoustic insulation has any thermal properties, but you'd have to prove it).
 
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Ok thanks a lot for feedback and the *******ing :) I will stick with 100mm Rockwool cavity in the 100mm cavity between the 2 skins, assuming I push into place as its a 100mm into 100mm, also then I will add 50mm internal on the inside walls then plasterboard.
Thanks
 
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my freind built his summerhouse and used 75mm rockwool all round so he could practice drumming in it
he was thoroughly disappointed when i walked past the back in the next door back garden talking to someone and the conversation was easily heard
off course i pointed out sheet material and a frame backed with sheet material and cladding was a good sounding board
 
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To avoid the sounding board, build a timber frame that sits on neoprene inside the brick structure . Do NOT fix it to the brickwork. Fill the timber frame with rockwool and plasterboard it. Ideally two layers of PB. Use filler on all PB joints- Skim.
The idea is two independant boxes - one inside another- with no mechanical fixings breaching the gaps
 
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