thinnest profile of insulation when room width is a concern

[JKami84]

I have a garage which I am sectioning to make some of it into a utility. 

One wall adjoins neighbours garage which i am thinking of options without losing hardly any width...

 

Neighbours have already done a "conversion" on part of their garage that covers half of the wall i will use for utility, and this entails them using 50mm celotex on their side of the 9 inch wall that seperates us. 

My builder (who also did our neighbours) says I really don't need to insulate, because neighbours already have. However, now we notice their insulation only covers half of my utility space I am wondering if its worth doing something at least on my side - and this could also potentially include a 12.5mm acoustic plasterboard to be used just to help incase the lads want to have a drink in this space from time to time, because it will be a nice space.

 

I told builder to go ahead and put 25mm celotex. I thought this meant 25mm celotex  + 12.5mm plasterboard (which I'd upgrade to acoustic)... and thought thats 37.5mm, and great. 

 

However... I got this wron. He has used 6x4cm battons. these sit 4cm from the wall, or 4.5cm in some parts, and the plasterboard would be on top. Now its looking like losing nearly 6cm of width from my room that I wasn't prepared to do. All he has done so far is batton the wall. I am thinking of next steps...

 

Is this 4cm the right amount to put 25mm of celotex? 

Is there a thinner way to do this?

When i questionned it, he said even if he did a "dot and dab" technique, that it would be thick (I assume he means adhesive) and it would still come out a similar amount. 

If I was to skip 25mm celotex but still wanted a 12.5mm acoustic plasterboard, I now imagine this would also not be 12.5mm total space because of need of adhesive or can they not just be drilled into the brick wall?

I'm not overly concerned with insulation, i just thought something would give me peace of mind. I would like to use 12.5mm acoustic plasterboard though if possible.

Other option is to do nothing. I just don't want regrets. 

 

My questions are, what is thinnest way to have some insulation with a plasterboard so it doesnt take up 6cm 

And is there a way to just have a plasterboard to only use up the 12.5mm thickness that they are.

 

 

 

 

[Iceverge]

I'm assuming that the wall between you and your neighbours is a solid 225mm block/brick wall?

 

If so the acoustic plasterboard won't make much difference as you already have lots of mass there. More important for noise is ensuring all air pathways are sealed 100% and then decoupling the walls to prevent any transmission of noise through the structure, think a stand off stud/resilient bars.  ( You shouldn't need to do this if it's a cavity wall)

 

Once the noise is catered for, and you really really really need the room space insulated plasterboard is probably the goto, dot and dab or mechanical fixed. It is silly expensive mind you for the thinnest stuff. 

 

 

 

 

 

 

[Ferdinand]

You need to check what building regs you are subject to.

 

If it is part of the dwelling, then you will need to insulate the wall to outside to the appropriate standard, as there are requirements to improve when you work on a thermal element of the building.

 

Your local council are the people to ask.

 

F

[JKami84]

@Iceverge thank you for an informative response. Yes it is a 225mm solid brick wall and they have 50mm celotex and standard plasterboard on their side. 

You talk of airgaps - well our ceiling is down and above the wall is hollow across neighbours garage roof (see image). They've packed their habitable part of their garage ceiling with insulation and we will pack with insulation too.

I could buy a different "upgraded" insulating rockwool product to "stuff" above the 225mm brick wall section that separates us? And use the normal insulation on rest of the ceiling. Do you think that would make any acoustic difference?

 

As to dot and dab. How much space does that take? Because if dot and dab takes about 15-20mm and then so does your 32.5mm product you showed me, then I may aswell continue with what's been started with 40mm battening with 25mm celotex (I am also going to Ask why he  cant get 30mm celotex in this space? E.g. he has 40mm of space from the wall to play with right.). 

 

I know I am being pedantic here.

.. but All I want is the best return on losing some width. 

 

If acoustic plasterboard alone would make no difference as you say. Then I may aswell do nothing. But if I do insulate then I may aswell use acoustic plasterboard anyway for minor price difference. 

 

[PeterW]

6 minutes ago, JKami84 said:

You talk of airgaps - well our ceiling is down and above the wall is hollow across neighbours garage roof (see image). They've packed their habitable part of their garage ceiling with insulation and we will pack with insulation too.

that is a big fire risk. There should be a fire barrier at the top of that wall - in the event of a fire in either property you could get spread of smoke or flame between units. 
 

7 minutes ago, JKami84 said:

but All I want is the best return on losing some width

At what cost ..?? Aerogel will give you the most thermal performance but would cost thousands for that wall. 
 

If he has battened out to 38/40mm then I would put 35mm Celotex in the spacing and then board over it but that does not meet anywhere close to building regulations and it will always be a cold room. 
 

What is happening to the floor ..??

[JKami84]

@PeterW could you give me a product for fireproofing? 

Would 50mm FR board be sufficient?

 

I know it will be a cold room. We are just sectioning some off for utility. I am just making it as cosey as I can (not spend thousands) but just spend money on what is worthwhile. 

DPM, 6mm fibreboard and 12mm laminate on the floor. Again just for comfort on the foot. It's a utility part of the garage that's all.