smart51 Posted September 7, 2022 Share Posted September 7, 2022 I'm planning a new build that will have a flat roof with something like an 8° pitch. I want to avoid it being noisy. We currently have a loft conversion. The roof is made of 175mm timbers with a plywood deck and EDPM covering, plasterboard underneath and foam board insulation between. Birds walking across the top are loud and so is rain. I guess the whole think is like a drum skin. How do you make flat rooves quiet? My guess would be that pitched rooves have separate timbers supporting the tiles and the ceiling. Two sets of timbers sound expensive. What are people's experiences with posi-joists? Are they equally noisy or do they acoustically separate the plaster board from the roof deck? Link to comment Share on other sites More sharing options...
nod Posted September 7, 2022 Share Posted September 7, 2022 All of the above Plenty of insulation Then you need to install an MF ceiling 100 mill below With 25 mil of acoustic insulation in the void One layer 15 plasterboard will make a massive difference Link to comment Share on other sites More sharing options...
Temp Posted September 7, 2022 Share Posted September 7, 2022 For stud walls one technique to reduce sound transmission is to have two staggered sets of studs, each supporting the plasterboard on one side. That way no sound transmitted through the studwork. Sound insulation can be woven between the two sets of studs. Sometimes two layers of plasterboard are used each side to increase the mass. Applying that to a flat roof you would effectively add a false ceiling. Eg one deep set of rafters would support the thermal insulation, OSB and EPDM etc. Then below/between that another set of ceiling joists (can be less deep) supporting just the plasterboard. if its a warm roof (all thermal insulation above the rafters not between) then this would increase the depth of the roof by perhaps another 50-75mm. Again sound insulation would be woven between the two sets. Another possibility would be to use resilient bars between the regular rafters and plasterboard, possibly doubling up the plasterboard to increase its mass. That would probably add 25-30mm. 1 Link to comment Share on other sites More sharing options...
JohnMo Posted September 7, 2022 Share Posted September 7, 2022 Our flattish roofs 12degs. EPDM/PVC with fleece below, 18mm ply, posi rafter 256mm deep. Underdraw with 2x counter 50mm battens, full filled with spray foam insulation. Then vapour control airtight membrane and a further 50mm counter batten and then 12.5mm plasterboard. Rain is a soft patter not intrusive, strangely you can hear grows on the roof but nothing else. 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted September 7, 2022 Share Posted September 7, 2022 3 hours ago, smart51 said: I'm planning a new build that will have a flat roof with something like an 8° pitch. Good to hear. You have quite a lot of options with a new roof. Existing roofs are a bit trickier as you invariably end up adding more load to the roof so you need to check this out SE wise. I have a warm flat roof on part of the house. Starting from the underside. Skimmed plasterboard, 195 x 45 timbers @ ~600 centres, 18mm timber sheeting, vapour barrier, 200mm of PIR, 18mm timber sheeting and then EPDM. Yes.. you can hear birds etc trundling about and heavy rain, but we have a roof lantern and like to hear the weather and wild life. This roof is over our living area.. would be different if over the bedrooms, worse if you live by the sea and have gulls waking you up at 3.00 am at times. Yes you can put an acoustic make up on the inside under the main joists. Problem is that if you have a lantern the roof thickness becomes even more of an issue. But you can also use a Sedum roof. That will act as a good cushion. You can make an allowance for a bit of extra load. As I have put an extra layer of sheeting directly under the EPDM I could also put some thin slabs on runners or stools on top of the EPDM.. less risk of a puncture, again this I think this would work well. We are plagued with slugs here so have an idea of putting some small plant pots etc up there for a bit of fun. Yes it may mean that you need a few extra timbers at closer centres. But the good thing about a warm roof is that you can do this without loosing performance due to repeating bridging of the joists, all the wood is on the warm side so it has no impact on the performance of the roof. The good thing about the above is that often you find that when you are interfacing a new roof with an existing house it ends up too high and you can't flash it in easily under the upstairs windows. Also, with a lantern you often need a 150mm kerb. If you put sedum or slabs on top you keep them back from the perimeter a bit so you still get the kerbs and flashings to work as you have not increased the roof thickness where you struggle for height. There is another benefit around putting stuff on top and setting it back a bit. It can soften the roof edge and help you not end up with fascia's and verges that look unpleasantly deep. Lastly you can also look at inverted roofs... these are more common on commercial stuff and can be tricky re drainage etc. Have a look maybe to just rule that option out. 1 Link to comment Share on other sites More sharing options...
Happy Valley Posted September 7, 2022 Share Posted September 7, 2022 We have a 10 degree monopitch warm roof (not the garage). It's steel. There is no noise at all inside. It is very well insulated and there is a void between the roof and the ceilings. BTW you'll need oversized gutters/downpipes. 2 Link to comment Share on other sites More sharing options...
smart51 Posted September 7, 2022 Author Share Posted September 7, 2022 14 minutes ago, Happy Valley said: We have a 10 degree monopitch warm roof (not the garage). It's steel. There is no noise at all inside. It is very well insulated and there is a void between the roof and the ceilings. BTW you'll need oversized gutters/downpipes. I suspect it is the void between the roof and the ceiling that silences the rain. Nice looking house BTW. 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted September 7, 2022 Share Posted September 7, 2022 1 hour ago, Happy Valley said: We have a 10 degree monopitch warm roof (not the garage). It's steel. There is no noise at all inside. It is very well insulated and there is a void between the roof and the ceilings. BTW you'll need oversized gutters/downpipes. Cool. Are the gallows brackets structural? Link to comment Share on other sites More sharing options...
Happy Valley Posted September 7, 2022 Share Posted September 7, 2022 3 minutes ago, Gus Potter said: Cool. Are the gallows brackets structural? Yes, they hold up a warm flat roof of about 1 meter. There's a hidden steel box section on top of the gallows running the full length along the front. 1 Link to comment Share on other sites More sharing options...
Gus Potter Posted September 7, 2022 Share Posted September 7, 2022 Like it! Some pretty smart lazer cutting there in the webs. Can I be rude and ask what the brackets cost? 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted September 7, 2022 Share Posted September 7, 2022 Put posi-joists in and create a 400mm void. Pump it full of cellulose and it will be graveyard quiet and very well insulated. Still run with resilient bars and 15mm SB plasterboard for cherry on ‘t cake. On another MBC PH TF atm and the silence inside is remarkable. 1 Link to comment Share on other sites More sharing options...
Happy Valley Posted September 8, 2022 Share Posted September 8, 2022 (edited) 10 hours ago, Gus Potter said: Like it! Some pretty smart lazer cutting there in the webs. Can I be rude and ask what the brackets cost? The 3 brackets (all with different cut outs) together with hidden stainless fixing points behind and all the box work (everything galvanised) was in the region of £3000 Edited September 8, 2022 by Happy Valley Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now