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Garage conversion wall insulation


tvrulesme
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Could someone please sense check this insulation for a solid wall for a garage conversion. I have asked building control but they said they weren't interested.

 

1494384181_Screenshot2022-01-09at08_10_52.thumb.png.b4e61efc6533656b938a45f04de4abe9.png

 

Things I'm not sure about.

  • I have a very small air gap but I think this is countered by the breather membrane, does this make sense?
  • Using uncoated PIR (thinking this General-Purpose-Polystyrene to save quite a few pounds) between the battens because the outer layer of PIR will be coated and act as the vapour barrier.  

 

Apologies have asked this question before but slight change here in the makeup so want to make sure I get it right.

 

Thanks in advance

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Just now, PeterW said:

I I’d want a vapour barrier in there - could be as simple as Aluminium foil taping all the joints on the 25mm layer as it is installed. 

 

Thanks Peter. Yes absolutely. Will be taping all the joints with foil. The rest looks ok?

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Only minor amendment I would make is to make your 13mm spacers from ply, and make them wider than your studs. Unless there is some really (structural) reason, 4x2 on the flat is overkill and you could use 3x2 and then make the frame on the floor. Put your membrane over and staple it then use say 6” strips of ply at each stud top to bottom, then when you stand it up against the wall your insulation will push tight against the ply and not bridge the very small gap. Belt and braces would be 13mm ply with DPC stapled down the back of it too. 
 

How is this being held against the wall ..? 

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8 minutes ago, PeterW said:

Only minor amendment I would make is to make your 13mm spacers from ply, and make them wider than your studs. Unless there is some really (structural) reason, 4x2 on the flat is overkill and you could use 3x2 and then make the frame on the floor. Put your membrane over and staple it then use say 6” strips of ply at each stud top to bottom, then when you stand it up against the wall your insulation will push tight against the ply and not bridge the very small gap. Belt and braces would be 13mm ply with DPC stapled down the back of it too. 
 

How is this being held against the wall ..? 

 

Thanks a lot. Sorry for being a dimwit but assume you mean the battens/studs? I was going to use this cls https://www.wickes.co.uk/Wickes-Studwork-CLS-Timber---38-x-63-x-2400mm/p/107177 because it's dirt cheap and strong. There will be a boiler attached to the wall (making sure I get the studs in the right place) as well as other things which will need a bit of structural oomf so wanted to use something with some strength

 

Concrete screws to attach to the wall

 

13mm spacers sounds like a great idea. Will just rip some cheap battens for this

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Think you need to check your measurements as 38mm on the flat is too little and 63 is too much if you’re going down the route of 50mm (which can be 48-53mm) PIR. 
 

I am thinking flat plats of Ply - think of a T shape - which will also give you some rigidity. 

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4 minutes ago, Roundtuit said:

You've linked to EPS rather than PIR/PUR insulation; that's quite different in terms of performance, and as @PeterW suggests, I wouldn't use anything less than 3x2 (75 x 50mm) for studwork.

 

Great thank you so this for studwork? It says "Please note: Finished size is 63 x 38mm" which is why I put down the 63mm

https://www.selcobw.com/products/timber-mdf-sheet-materials/cls-timber/cls-softwood-studding-75-x-50mm-3-x-2-nom-pefc

 

And you're right, I should not skimp on the PIR for between rafters. I wasn't aware there was such a perf difference. Thanks a lot

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7 minutes ago, PeterW said:

Think you need to check your measurements as 38mm on the flat is too little and 63 is too much if you’re going down the route of 50mm (which can be 48-53mm) PIR. 
 

I am thinking flat plats of Ply - think of a T shape - which will also give you some rigidity. 

 

I was thinking something like this from a kingspan video using the 75mm (63mm finished) studs

 

Screenshot_2022-01-09_at_09_37_56.thumb.png.02974b3f9287fc2cef4c9534b18b297f.png

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