Internal garage partial conversion

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Hi,
Could someone advise on the following please?

I have an internal garage that I'm partitioning to create office space. One side is an external wall to a passageway into my garden, front is an up&over garage door, other two walls are internal.

A local building inspector paid me a visit and verbally advised;
Floor - DPM + 70mm foil backed insulation - fine with that, I plan to add 100mm + 22mm T&G to create floating floor to new level.

Outside Wall - It's a 70mm cavity with insulation - advised I need to add an additional 20mm (insulated plasterboard) - PITA, but OK with that.

Main issue is the partition wall - He advised, 100mm studwork, foil backed insulation between stud, + fire board garage side + thermal board room side.

For the insulation, I see most people reference something like Celotex GA4000. However, I've read it's doesn't supress noise well.

Q1: Could I use Rockwool 100mm Rockwool Sound Insulation Slab 1200mm x 600mm, or perhaps Celotex with a Knauf Sound Panel Tapered Edge - 12.5mm x 1.2m

Q2: Could I use just OSB3 board for the room side, as the wall will have some monitors attached and I believe plasterboard isn't ideal. Maybe OSB3 over the sound panel board (or is this excessive)

Basically, I need to get insulation to the required regs, but also to sound proof the room as best as possible.

I've tried to draw it out, but I'm no expert.
Partition Wall - Side Evelvation.png


Any thoughts or advice welcome?

Ta.
 
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You will need a PIR insulation product unless you want to double the wall thickness and use alternatives.

Be clear about what you are trying to insulate from sound, noise getting in or out, as that determines which side you need to insulate for sound.

And don't get too hung up on sound insulation, as what you achieve with the the various layers you mention and PIR, may not be much different to any additional sound insulation that could be practically added.

Chipboard on its own is not fire resistant.
 
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You will need a PIR insulation product unless you want to double the wall thickness and use alternatives.

Be clear about what you are trying to insulate from sound, noise getting in or out, as that determines which side you need to insulate for sound.

And don't get too hung up on sound insulation, as what you achieve with the the various layers you mention and PIR, may not be much different to any additional sound insulation that could be practically added.

Chipboard on its own is not fire resistant.
Thank for the reply Woody.

When you state "You will need a PIR insulation product unless you want to double the wall thickness and use alternatives", is this referring to attempting to use Rockwool as the insulation within the partition? I'm assuming so as it's thermal properties isn't as good a Celotex - right (from what I read)?

The part that's really confusing me is he stated "plus thermal board office side". Does this mean I need more insulation than the 100mm Celotex (in the studwork)?

I'm near a main road so need to primarily isolate noise coming in (from the original garage side), although it will be used for music too, so great if I can stop too much getting out (although its a detached house so not so important). Hence, think of using sound panel for the Office side, but if I need additional insulation (as mentioned above), maybe not?

The reference to OSB was purely to put on the office side wall over whatever is needed legally, so I can fix appliances more securely. The inspector stated the fireboard needs to go on the garage side only.

Hope that makes sense?
 
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The part that's really confusing me is he stated "plus thermal board office side". Does this mean I need more insulation than the 100mm Celotex (in the studwork)?
Yes. You need to prevent cold bridging (shadowing) through the studs and is important. It need not be on the office side. In fact I'd prefer to see it on the cold side - thus deeming the frame/studding a 'warm' frame.
 
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The garage door and walls will attenuate sound, so you won't really need additional measures to the planned lining. You don't really need fire rated plasterboard as normal 12.5mm board and skim will be sufficient. Use a sound check plasterboard (blue) if you prefer. Otherwise you are into randomly trying to add layers of this or that, without actually knowing if they are providing any discernible benefit.

Insulate across the frame on the warm side with either a 30mm layer of PIR and plasterboard or thermal board to provide the necessary thermal value and prevent pattern staining of the frame. Plasterboard will hold monitors no problem, or fit noggins or ply to the frame.
 

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