Thoughts of single leaf v double leaf and loss of head heigh

[LSB]

hi,

I’m building a garden studio in the UK under permitted development which limited my roof height.

My requirement for isolation is 45db. I’m planing a double leaf construction The construction is as follow

OSB& cladding >> insulation bats >air gap >> 15mm drywall > green glue > 12.5mm drywall

With the ceiling was planning on replacing the air gap with genie clips and RC.

However due to height restrictions that only gives me 2.05m head height, without clouds etc so this seems low.

One proposal is to use a cold deck roof system, this saves me 12cm, however this needs to be vented. This means my ceiling system is effectively a single leaf. My thoughts are I could take out the clips and go for a ceiling that is

OSB>15mm drywall > GG > drywall x2 - so effecitly a thicker single leaf.

Any thoughts on whether this is a good compromise or will undermine my whole system? Or should I accept the low ceiling

Welcome any thoughts, thanks

[Soundman2020]

OSB& cladding >> insulation bats >air gap >> 15mm drywall > green glue > 12.5mm drywall

You'll need some studs in there somewhere! Where are you planning to put them, and how big are they? Also, there's no advantage to having one layer of 15mm and another layer of 12.5mm. Yes, there is a slight improvement due to the different thicknesses, but that is offset by the lost mass. Make them both 15mm.

With the ceiling was planning on replacing the air gap with genie clips and RC.

Ditto: You need joists up there somewhere... Where are you planning to put them, and how big are they?

OSB>15mm drywall > GG > drywall x2 - so effecitly a thicker single leaf.

... and effectively isolation of about 35 dB... That's all you'll get from three layers of drywall...

When you have to have a vented roof deck, then there's not much choice: you are forced to have a three-leaf ceiling, where there's a "middle leaf" that completes the outer leaf envelope to provide continuity of mass and air-tight seals. That implies that you have to compensate for the third-lead problem by adding more mass to the middle leaf, and increasing the air gaps.

Any thoughts on whether this is a good compromise or will undermine my whole system? Or should I accept the low ceiling

Permitted development Class E sets the height of the eaves, and the height of the roof peak, not the height of the ceiling. That height is 2.5m for the eaves, 3m for the roof peak:

Permitted-development-eaves-extract.jpg

If you design your roof structure carefully, you should be able to get a ceiling height much higher than 2.05m.

Also, there's no restriction on digging down a bit, so your floor is below ground level. That allows you to have any height ceiling that you feel like.

- Stuart -

[LSB]

Thanks for your answers

Sorry yes 8 inch studs for ceiling

4 inch studs for walls.

Re permitted development. It’s within 2 metres of boundary so height can be a maximum of 2.5m - we’ve already dug down a bit so the concrete base is underground level, also we’re pushing the interpretation a little bit about why the ground level height is.

So that’s given the option to use a warm deck roof 2x OSB as one layer, 8 inch stud. Genie clips & RC - 2 layers of plasterboard with GG in the middle for the ceiling and get slightly more head height

Secondly, I’m toying between having 2 x plasterboard with Green glue attached to 4 inch studs with acoustic bat insulation and an external OSB leaf. Having this as opposed to the dual leaf, since this is the same system as my ceiling it seems futile to go for the dual stud approach as th system will be compromise by the ceiling. I’d also gain 30cm of floor space on both the length and width.

Any thoughts on this. I’m confused tbh.

Full studio dimensions 5m x 3.8m x2.1-2.2 - it’s a production room

[Gregwor]

Any thoughts on this. I’m confused tbh.

You're going to have a hard time achieving your desired isolation without a fully decoupled MSM system. Do the math using mass law to see what you're up against.

If I were you, I'd build an inside out ceiling because using clips like you described, you're going to end up with a hard reflective ceiling that you're going to need to hang a bunch of insulation on and end up having a visually low ceiling anyway. Building inside out kills two birds with one stone. And lastly, if height is an issue, dig into the ground deeper. It's that simple.

Greg