Studio Conversion 2 - Air Gap issue

[geoff_fry01]

Hi guys, with your guys help I converted my previous garage into a very will soundproofed Drum Room (about 15 years ago.) However I have now moved house and am now working on Studio 2.
I have hit a problem... due to a bit of bad communication I now have a wooden shell allowing a 5' gap between inner and outer leaf on the sides (as planned) BUT only 3.5inch in between the ceiling leafs.

I cant find many post saying one way or another how much difference there might be between an 5' or 3.5' gap, Though I do read that the bigger the gap the better and the bigger the gap the better low frequencies are stopped?

The space is limited so I decided on a 5" gap all around.

So my question is
1. what difference does a 5' to 3.5' make?

or 2. what would you do?

Few obvious options I have considered, I can rip the whole lot down and start again. many man hours and £££ wasted
or I can continue with the 3.5' gap on the ceiling and change the planned 100mm rockwool for 50mm rockwool (the inner leaf is to be 2 layers of 12.5 boards plus greenglue.) (the layer above the inner room is to layers of plasterboards with green glue and is also hung from the garage rafters on genie clips.
or I guess I could put more wood (3x2's) on the underside of the current inner room ceiling and to bring the layers apart to 5" (or use genie clips).. any help or advice gladly received.

some pictures below for better ref.

20210614_135536-800.jpg

20210614_135552-800.jpg

before-800.jpg

full studio-800.jpg

Thanks
Geoff

[gullfo]

the air gap is helpful and if you can go larger that's good, however, the 2" difference is going to matter less than the mass on either side of that gap, and an coincident resonances, etc which limit the transmission loss.

so i'd keep going.

[geoff_fry01]

thanks Glenn appreciate your time and thoughts!

[Paulus87]

full studio-800.jpg

Thanks
Geoff

It looks like you have a three leaf assembly - Outer brick, middle block and then a inner plasterboard leaf. Just wondering why that was necessary?

[DanDan]

In all cases it is best to fill the gap entirely with fibre. Light cheap rolls work exactly as well as rigid batts. But fill fully,

[geoff_fry01]

In all cases it is best to fill the gap entirely with fibre. Light cheap rolls work exactly as well as rigid batts. But fill fully,

I seem to be getting different info on the Batts touching the outer leaf or having a gap. I have "thick enough" that I can have either option, at the moment the batts leave about a inch gap BUT they are easy enough to give a little "fluff up" and expand the full space.

So is the latest advice fully fill the gap?

Thanks
Geoff

[geoff_fry01]

full studio-800.jpg

Thanks
Geoff

It looks like you have a three leaf assembly - Outer brick, middle block and then a inner plasterboard leaf. Just wondering why that was necessary?

Hi Paul, for most builds I dont think it would not be necessary (infact for lots I understand it would be worse not better, but for my build the red brick has the pitched roof rafters literally sticking through it to the outside. I decided I didn't want to risk the sound going straight into the ceiling joists which at connected to the rafters and out the red brick so I used dense blocks in the hope that the '3 leaf effect' would be less from red and grey brick than from the flanking of the rafters. time will tell.

20210617_101936-800.jpg

[Paulus87]

full studio-800.jpg

Thanks
Geoff

It looks like you have a three leaf assembly - Outer brick, middle block and then a inner plasterboard leaf. Just wondering why that was necessary?

Hi Paul, for most builds I dont think it would not be necessary (infact for lots I understand it would be worse not better, but for my build the red brick has the pitched roof rafters literally sticking through it to the outside. I decided I didn't want to risk the sound going straight into the ceiling joists which at connected to the rafters and out the red brick so I used dense blocks in the hope that the '3 leaf effect' would be less from red and grey brick than from the flanking of the rafters. time will tell.

20210617_101936-800.jpg

So third leaf effect aside - have you taken in to account interstitial condensation risk? I can't see exactly what is going on but suffice it to say that as long as you have either a vented cold roof or a warm roof design then you will be ok. If you are not sure or have something different to that then you may end up with condensation building up under your roof deck which will rot out your timbers without you ever being able to see it until it's too late.

I am not saying this to be a party pooper, I am just saying it to help you in the long run as it is becoming more and more common to see many failed builds due to this issue alone - it is not talked about enough on the forums - probably as it has very little to do with acoustics and isolation, but it has everything to do with structural integrity.

[geoff_fry01]

yea its vented. you might see on pic. c. 10mm mesh around edge

[Paulus87]

yea its vented. you might see on pic. c. 10mm mesh around edge

Excellent