Sound proofing a warm flat roof

[Alex]

Hi All, 

 

Got a question I'm struggling to find an answer too...  I have a flat roof (warm construction) so all the insulation is on top of joists/rafters (never know which term to use for flat roofs!). The space under the flat roof is divided into a 2 rooms by a timber stud wall. As I understand things the space between the joists is left as a void as insulation is above this so to avoid condensation issues. One of these rooms is  our utility room with washing machine/tumber drier in it, which seem to be on almost constantly! 

 

The question I have is can I pack out the void with acoustic insulation above where the stud wall meets the ceiling? I'm insulating the wall but am concerned that at the ceiling there's nothing to stop the sound travelling between rooms over the wall other than plaster board. We've switched some rooms around and the room next to the laundry is now going to be my office so want it as sound proofed as possible.

For info the stud wall, whilst running parallel to joists doesn't come up directly under a joist so has a number of noggins running perpendicular to it that it is going use as fixing points.  Joists are at 400mm centres. What I was think was just filling that space between these 2 joists with acoustic insulation so that there is some soundproofing above and to either side in the ceiling above the stud wall. 

 

Anyone see any issue with this? and should I leave air gap above the insulation or completely fill void (joists 200mm deep)? 

 

Thanks

A.

[ProDave]

I don't see an issue.

 

My "warm roof" has insulation over the rafters AND insulation in between them. This seems pretty normal on most builds now, and the design was accepted by building control. So I don't see why adding extra insulation as you suggest will cause an issue.

[nod]

1 hour ago, Alex said:

Hi All, 

 

Got a question I'm struggling to find an answer too...  I have a flat roof (warm construction) so all the insulation is on top of joists/rafters (never know which term to use for flat roofs!). The space under the flat roof is divided into a 2 rooms by a timber stud wall. As I understand things the space between the joists is left as a void as insulation is above this so to avoid condensation issues. One of these rooms is  our utility room with washing machine/tumber drier in it, which seem to be on almost constantly! 

 

The question I have is can I pack out the void with acoustic insulation above where the stud wall meets the ceiling? I'm insulating the wall but am concerned that at the ceiling there's nothing to stop the sound travelling between rooms over the wall other than plaster board. We've switched some rooms around and the room next to the laundry is now going to be my office so want it as sound proofed as possible.

For info the stud wall, whilst running parallel to joists doesn't come up directly under a joist so has a number of noggins running perpendicular to it that it is going use as fixing points.  Joists are at 400mm centres. What I was think was just filling that space between these 2 joists with acoustic insulation so that there is some soundproofing above and to either side in the ceiling above the stud wall. 

 

Anyone see any issue with this? and should I leave air gap above the insulation or completely fill void (joists 200mm deep)? 

 

Thanks

A.

I had the same issue 

BC told me As soon as you put insulation on top

ie warm roof construction 

Pack as much as you like underneath No air gap required 

[ADLIan]

In a warm pitched roof it is acceptable to put a limited amount of insulation between the rafters (depends on thermal resistance of this layer). In a warm flat roof additional insulation should not be used between the roof joists. Probably OK in a limited area, but keep to minimum above the wall head, to improve sound insulation.

[AliG]

Is the ceiling already built? If not why not run the stud wall right up to the insulation and seal it. This would considerably help sound travelling between the rooms.

[Alex]

On ‎05‎/‎01‎/‎2018 at 19:32, AliG said:

Is the ceiling already built? If not why not run the stud wall right up to the insulation and seal it. This would considerably help sound travelling between the rooms.

 

Stud isn't built as yet but I like that idea. So basically run the stud up to the underside of the roof deck and insulate the stud as normal. Can add some noggins to help brace the stud between the joists so nice a solid.

Thanks.

[Temp]

If the stud wall hasn't been built use two sets of studs one for each side like this with sound insulation. Ideally two layers of plasterboard both sides. View from above..

 

Edited January 8, 2018 by Temp

[Temp]

I would use deeper studs than normal to avoid needing noggins that could create a sound bridge.

[mvincentd]

Can I revive this thread @Alex and ask what you ended up doing and building control’s reaction?

I now face this same question with 373 deep x122wide posijoists at 400 centres.

thanks.

[Alex]

I ended up moving the stud wall slightly and running it under a joist. I insulated the wall with rookwool slabs and I also put rockwool either side of the joist. I didn't do with the design as shown by @Temp above but did double board on both sides.