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Airtight seal between PIR and slab


Hilldes
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About to start fixing PIR insulation sheets across the inside of the timber frame. Need a method of ceiling the foil on the PIR to the concrete slab (will have no screed). The foil of the PIR will be taped to form the VCL.

 

Timber frame company said they would normally prime the concrete slab with PVA, then use tape to seal this to the foil on the PIR - I'm assuming this is standard aluminium foil tape. Has anybody done this?

 

Are there any alternative approaches for ensuring an airtight seal at this junction?

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That would be my concern too @Big Jimbo.

 

Does anyone have an alternate solution please? I have searched both Buildhub and googled but can’t locate a solution. This must be a relatively standard detail.

Edited by Hilldes
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12 hours ago, Hilldes said:

About to start fixing PIR insulation sheets across the inside of the timber frame. Need a method of ceiling the foil on the PIR to the concrete slab (will have no screed). The foil of the PIR will be taped to form the VCL.

 

Timber frame company said they would normally prime the concrete slab with PVA, then use tape to seal this to the foil on the PIR - I'm assuming this is standard aluminium foil tape. Has anybody done this?

 

Are there any alternative approaches for ensuring an airtight seal at this junction?

This is exactly what I did. My sole plate had some adhesive + mechanical fixings. It then had adhesive/sealant between sole plate and timber frame sections. Then I primed the concrete and used the appropriate tape for wood to concrete and it is still like nobodies business 3 years on. My air test was 0.4 with a bug piece of window trim missing so it must have worked well

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42 minutes ago, Pete said:

This is exactly what I did. My sole plate had some adhesive + mechanical fixings. It then had adhesive/sealant between sole plate and timber frame sections. Then I primed the concrete and used the appropriate tape for wood to concrete and it is still like nobodies business 3 years on. My air test was 0.4 with a bug piece of window trim missing so it must have worked well

Thanks @Pete so you effectively sealed the timber frame to the concrete floor? - Did you use foil on PIR insulation as your VCL?

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43 minutes ago, keith65 said:

put a bead of air tight foam on the PIR then push it to the floor, but you will need to mist the concrete first with water to help the foam expand

Thanks @keith65 by "air tight foam" do you mean regular expanding foam?

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Timber frame sole plate to concrete slab sealed with this primer on concrete:

https://www.greenbuildingstore.co.uk/products/pro-clima-tescon-primer-rp/

 

And then taped all the way around a very long permiter with this:

https://www.greenbuildingstore.co.uk/products/pro-clima-tescon-vana/

 

Sticks like no-ones business, it's contact activated so make sure you use the blue scraper it comes with to press it down.  I then had a levelling screed go down, so that tape ain't moving, ever!

 

If you want a flexible airtight seal e.g. around soil pipe penetrations you can also use this (and tape if you want to go mad!):

https://www.greenbuildingstore.co.uk/products/pro-clima-orcon-f/

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13 hours ago, Hilldes said:

Thanks @Pete so you effectively sealed the timber frame to the concrete floor? - Did you use foil on PIR insulation as your VCL?

No, just an internal vcl as a complete barrier on its own

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