Timber room in a garage

[BojanL]

Building a timber music studio room in a single brick/breeze block garage, to act as a double wall (photo below).

30-50cm distance between the outer wall and inner studs - big cavity because of soundproofing technique as advised on music studio forums. Insulation in between with 10cm air gap + double plasterboard.


Do I need any DPM, vapor barrier or similar on the inner side of the studs?

I am thinking as there is a huge gap the air would circulate and flow through the soffit vents so no need for any membrane or such?

 

[noseall]

Building a timber music studio room in a single brick/breeze block garage, to act as a double wall (photo below).

30-50cm distance between the outer wall and inner studs - big cavity because of soundproofing technique as advised on music studio forums. Insulation in between with 10cm air gap + double plasterboard.


Do I need any DPM, vapor barrier or similar on the inner side of the studs?

I am thinking as there is a huge gap the air would circulate and flow through the soffit vents so no need for any membrane or such?

Depends how you insulate. You can effectively create a VCL using foil covered PIR and foil tape, along with Duplex plasterboards.

 

[BojanL]

Depends how you insulate. You can effectively create a VCL using foil covered PIR and foil tape, along with Duplex plasterboards.

Do I need a VLC if I put 20cm of fiberglass behind duplex plasterboards? 10cm gap between fiberglass & outer walls.

 

[^woody^]

With a brick external leaf and timber frame, the concept is to protect the frame (and insulation) from moisture entering the cavity from external, and also entering from the internal room as vapour or heat - which condenses to form moisture.

This is done via a membrane on the cavity side of the frame, and a vapour check layer on the room side of the frame.

The cavity should also be drained as well as vented, or the frame otherwise protected at floor level.

You will struggle now with protection on the cavity side of that frame, so there's a risk. If the external is rendered or clad, it may be OK, otherwise, if any of the external walls are brick and exposed to direct rain, consider coating them with a quality water repellant. In not sure that water repellant work on bare blockwork.

The frame is a bridge for sound. Ideally, your insulation should have been across the internal face, so you should consider that as an additional layer.

 

[Deluks]

The 30 - 50cm gap seems excessive, you will lose a lot of space that way. Although I see that you've already started, so you are where you are.
Good practice is to completely fill the air gap with insulation, the densest you can find, which is usually rockwool slab.
The downside to this is the risk of any moisture getting in making the insulation damp, this could be mitigated if you use an insulation product designed for full cavity fill.

I would err on the side of caution and leave an air gap, 50mm here would be plenty to deal with moisture penetration, although with your studs spaced so far away from the outer wall, I don't see how you'd fix it in place, you may need to build another stud wall close to the outer wall, just to build a supporting frame for the insulation.

You only need duplex plasterboard as the first layer, (or staple a sheet of polythene vapour barrier to the inside of the studs and use regular plasterboard)
Consider making your first layer out of MDF or OSB, then 2 layers of plasterboard on top of that. You can't rely on insulation alone to block sound, that's not really how it works. The change of density from plasterboard to wood will increase the range of frequencies that you will be blocking.

Also consider that if your soffit vents can pass air, they can also pass sound. Ideally you would have 2 way mechanical ventilation through an acoustic plenum chamber.
Consider fitting something like that now, or at least build in a way that you can easily retrofit later.

 

[BojanL]

With a brick external leaf and timber frame, the concept is to protect the frame (and insulation) from moisture entering the cavity from external, and also entering from the internal room as vapour or heat - which condenses to form moisture.

This is done via a membrane on the cavity side of the frame, and a vapour check layer on the room side of the frame.

The cavity should also be drained as well as vented, or the frame otherwise protected at floor level.

You will struggle now with protection on the cavity side of that frame, so there's a risk. If the external is rendered or clad, it may be OK, otherwise, if any of the external walls are brick and exposed to direct rain, consider coating them with a quality water repellant. In not sure that water repellant work on bare blockwork.

The frame is a bridge for sound. Ideally, your insulation should have been across the internal face, so you should consider that as an additional layer.

Cheers.

Soffit is completely open full length left & right 6cm, shouldn't that be enough for most of the moisture to be released and not cause any issues like damp/mold...?

Everything is rendered externally and painted except front wall (rendered internally) which sometimes has wet patches inside after rain but that dries completely in one day. My plan is to coat with water repellent and if that doesn't help I would rather do a thick render than any plastic sheets inside - my logic is better to prevent it getting in.

And yes, there is gonna be acoustic panels on plasterboard for the actual room sound - double wall is for noise isolation as it's residential area.