To flank or not to flank

[Studiobuild]

Hi folks, inexperienced builder doing a garden studio for music purposes.

Making a 6 by 4.5m studio in a limited space in my garden. I based the design on a tried and tested timber frame twin stud with Rockwool and double layer of plasterboard on the interior with green glue between the boards. So to be clear from outer to inner, wood cladding, OSB on timber stud with Rockwool, 1” gap, stud with Rockwool, double plasterboard with green glue. This will apparently give good acoustic isolation.

My problem is that I have dug down in order to gain internal height and can’t put timber below the DPC so have been advised to use concrete blocks up to soil level then put the timber stud on top of that. The concrete slab is in a hole with sloping sides so the depth goes from 50cm at one end to 1.3m at the other. I plan to lay the blocks on the flat at the deep end for strength but for the rest I will put them on edge.

Will a timber stud on a block wall be unstable?

I was going to do just the outer skin with block to ground level and the inner skin with timber right from the slab. Now I am worrying the blocks might be unstable without being tied in to another wall. I thought about doing blocks to the same height on the inner wall again with timber stud on top, so I could use wall ties between the blocks but I don’t want to get flanking issues with vibration going from the inner leaf through the ties into the outer blocks and straight into the timber stud above. I can’t find much info on how much type A ties will flank. Or how much the vibrations will make it through two layers of board, through a dense block and the up to the outer timber stud.

Oh and by the way the roof will be much the same as the walls except 7 by 2” rafters across the width.

Any thoughts would be hugely welcome.

 

[noseall]

a tried and tested timber frame twin stud with Rockwool and double layer of plasterboard

Never heard of it. What is twin stud?

Why are you using rockwool and not say foil sandwich PIR which is more efficient and can help deal with vapour control?

What considerations have you given to vapour control both internal and external?

the depth goes from 50cm at one end to 1.3m at the other. I plan to lay the blocks on the flat at the deep end for strength but for the rest I will put them on edge.

Are you saying the base is acting as a retaining wall? A sketch would give a better impression.​

 

[Studiobuild]

Hi thanks for replying. Re vapour control, I will have mechanical ventilation from the inside to outside but nothing from the space between the walls. I can’t have any openings in the outer skin other than doors for sound insulation and the two vents to the inner room.

re Rockwool, the mineral wool needs to be fully exposed to the air for the sound insulation system to work so no foil lined stuff.

yes the base as a retaining wall. Terrible sketch attached

 

[Studiobuild]

It’s based on the building shown in this YouTube vid. Perhaps will be more clear than my description

 

[Studiobuild]

Oh again re vapour, I will have an inner and outer door. I will have a 1” gap between the two which I will not seal across the threshold or between the architraves so hopefully this would be one way for moisture to evaporate from the void between the walls. This will be at the front and rear of the building, so two entrances, each with an inner and outer door. No windows.

I do have a DPM in place to bring up above the blocks on the outside but open to further ideas on stopping moisture coming through.