Room within a room - Can't fit decoupled joists - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 10 Old 01-09-2020, 05:19 AM - Thread Starter
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Room within a room - Can't fit decoupled joists

We are having a new extension built. It will include a small cinema room, see pictures. https://www.avsforum.com/forum/attac...666946&thumb=1
https://www.avsforum.com/forum/attac...666948&thumb=1

On that rough plan of the room:
Left wall and top wall are new exterior walls (1 ft thick, concrete block and brick with cavity)
Bottom wall is existing exterior wall (1ft) , kitchen is on the other side.
Right hand wall is new interior wall - 4" concrete block.

Original plan was to build a room within a room, 2x4 timber, 2 layer PB and then sit independent joists on that structure, spaced between the joists of the new roof. As per the diagram (Sketchup). https://www.avsforum.com/forum/attac...666958&thumb=1

BUT.. architect/Building Control has specced timber binders on top of the joists due to the span - so I can't put my joists in between as the roof joists will be in the way of the binders for the cinema ceiling joists. I also can't afford to lose headroom by having them underneath.

If I keep the walls decoupled, but fix them to the ceiling joists, I'm worried about noise transferring along those joists to the wall plate and resonating in to the main house. Another option would be to do this but then decouple the ceiling boards using clips and channel? I just thought this added complication for the builder and more to go wrong....
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Last edited by Harkon; 01-09-2020 at 05:21 AM. Reason: missing picture
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post #2 of 10 Old 01-09-2020, 05:28 AM
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build the wall framing one inch short and anchor the top plate with IB3 clips, If you can slip rubber pads under the bottom plate do it. This will keep the wall decoupled from the ceiling joists and floor, then use a clip and channel system to decouple the ceiling PB. Consider using Green Glue between layers of PB. It is a dampening layer not a glue.



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post #3 of 10 Old 01-09-2020, 06:16 AM - Thread Starter
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Thanks Big, really appreciate your advice/experience.

Any acoustic rubber mat? Seems to come from 1mm up to like 5mm thick.

I need to see if there is a UK supplier of IB3 clips and also clips and channel. If not order from Sound Proofing company and pay for shipping.
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post #4 of 10 Old 01-09-2020, 06:19 AM
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the thicker the rubber the better, here we can easily get horse stall mats (or gym mats) that are 1/2 to 3/4 inch thick and cut into strips with a hook nose utility blade.


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post #5 of 10 Old 01-09-2020, 07:32 AM
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With the rubber mats, do you rely on the weight of the wall to hold it in place on top of the mats, or do you secure it by running nails or bolts through the base of the framing into the subfloor?
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post #6 of 10 Old 01-09-2020, 09:27 AM
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you will still need a few nails/screws to satisfy an inspector, If they want a lot I would do screws than after you pass inspection back most of them out.
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post #7 of 10 Old 01-09-2020, 12:52 PM
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Quote:
Originally Posted by HunterG View Post
With the rubber mats, do you rely on the weight of the wall to hold it in place on top of the mats, or do you secure it by running nails or bolts through the base of the framing into the subfloor?
I just ran standard masonry nails right through them IIRC I went with 3" long and my mats were from TSC
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post #8 of 10 Old 01-10-2020, 04:13 AM - Thread Starter
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Quote:
Originally Posted by BIGmouthinDC View Post
build the wall framing one inch short and anchor the top plate with IB3 clips, If you can slip rubber pads under the bottom plate do it. This will keep the wall decoupled from the ceiling joists and floor, then use a clip and channel system to decouple the ceiling PB. Consider using Green Glue between layers of PB. It is a dampening layer not a glue.


Big

I've emailed a few companies to see if I can source decoupling brackets in the UK. I found these on Amazon which look similar?
https://www.amazon.co.uk/Acoustic-Br...pcontext&psc=1

What do you think?
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post #9 of 10 Old 01-10-2020, 05:02 AM
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They look fine, you only need one at the corners and every 4 ft. I also add one directly over the hinge side of door framing, 100 will do four or more theaters
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post #10 of 10 Old 01-15-2020, 09:34 AM
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looking forward to following this thread and learning more about building a room inside a room and so on.

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