I want sound isolation and light PART II

[Almavague]

Hello all – I’m starting a new thread even though I’m continuing the same project. Hopefully it will make things simpler for anyone who wants to chime in without reading the whole previous thread. First off, many thanks to Glenn and Stuart for their great advice!

Here’s a summary of the project to date:
The original building is a barn attached to my house that is being converted for a rehearsal/teaching space. The goals are 50db sound reduction and allowing the south sun into the space. The original barn is made of 50cm pisé (rammed earth – very massive) with a wood beam structure supporting a tiled roof. The roof tiles keep out most of the rain, but are totally porous to sound. So to complete the outer leaf, I build a false ceiling out of 13mm OSB, and put 20cm of insulation above it.
Inside, I build a wood structure (framed walls and ceiling), decoupled from the barn walls/false ceiling. It’s sitting on a concrete slab that makes up the floor of the barn. The wood structure has a 4cm air gap with the barn walls, 145cm of wood fiber insulation and 2 layers of 13mm acoustic drywall. So the layers from outside to inside are: pise 50cm, air gap 4cm, wood fiber insulation 14.5cm, drywall 2.6cm.

Everything is well caulked. The door for the inner leaf is a sliding glass door (medium quality, I bought it used)
The unfinished part (see the photos) is the former “barn door opening” in the outer leaf. My plan is to do wood framing, with more wood fiber insulation, layers of acoustic drywall, with an outer layer of osb to protect from the elements. The main door is another that I bought used – it’s a unit with 2 French doors and a fixed window. The two doors and the leaves in this part of the structure are about 40cm apart.
I’m thinking that the osb will be the semi finished exterior for a number of years, until I redo the whole siding of the house, possibly years in the future. One day I’ll either cover it with render or wood siding. I believe the osb should be sufficiently weather proof. This part of the building is relatively well covered by a large roof overhang, so very little rain, etc. gets this far. I’ll probably paint/stain it to make it look acceptable for the time being.

Here are my questions:
- I presume used door will get around 25-30db of reduction, and I also presume that there’s no reason build outer wall for higher reduction than the door. Is this correct? Or would I be better off shooting a little higher on the wall sound isolation?

- Based on the answer to the previous question , how many layers of drywall do I need?

- Is osb a good material for this outer layer? If not, what?

- How would I seal the base of the osb and the cement slab ground? Is caulk sufficient? Or is there a better technique given that this is probably the spot most likely to be damaged by water, foot traffic, etc.?

- I’ll have odd gaps to fill between the wood framing/drywall/osb edge and the old barn wall made of wood, stone, cinderblock etc (photos may help to see this). I think the standard material to seal uneven surfaces like this is expanding foam. I’m not a big fan of this stuff for its environmental impact, and it may show on the outside because I’m not really “finishing” my exterior. Are there alternatives?

Many thanks in advance.

[gullfo]

using exterior grade products which have moisture protection is advisable for the lowest parts of the framing and panels. so check for treated products which are allowed (some countries have different treatment chemicals allowed). then on the exterior, i would try to mimic the rock surface where possible. on the inside - you will seal everything. seal everything. seal everything. then as far as interior sound isolation - depending - you want to match the mass all around, this may implie on walls and ceiling where the construction is lighter, you need to add mass (layers of drywall? etc) then your interior walls will be straightforward - the mass can be consistent (e.g. 2x layers of drywall) all around (ceiling, walls).