Vcl laying method warm roof

ThrottleHappy · 20 Nov 2020

Hi guys.

I have some some questions that are likley silly but here goes

I am laying my final layer of t&g boards tomorrow. I already have my firrings and sub t&g deck layed.

Tomorrow weather permitted is to get the vcl put down onto the deck, ready for the celotex to go on top. This will get sandwiched by a final layer of osb then grp..

So first question is, when i bring the sides of the visqueen up and over the celotex board, all the way round each of the sides, am i making this air tight by fully taping the polythene to the celotex or, just holding it in place?

Second question, the polythene is 4mx25 so obviously i need to tape it with poly tape, no problem i got some really sticky $ht! Do i need to go over the top and make 'waterproof' so to speak or just tape it and forget about it. I can see myself taping the hell out of it

Third question.. i will be putting expanding foam betweed the celotex butt joints, then sealing with foil tape so it will end up like a continuous board. Should i seal the exposed sides of the celotex at the perimiter or is this a nono?

Obviously im trying to keep the boards dry by going over the top on visqueen while not working on it. Should the rain get under at any point, will it work it's way out?

I really have searched on this but cant get definitive answers

Notch7 · 20 Nov 2020

ThrottleHappy said:
Hi guys.

I have some some questions that are likley silly but here goes

I am laying my final layer of t&g boards tomorrow. I already have my firrings and sub t&g deck layed.

Tomorrow weather permitted is to get the vcl put down onto the deck, ready for the celotex to go on top. This will get sandwiched by a final layer of osb then grp..

So first question is, when i bring the sides of the visqueen up and over the celotex board, all the way round each of the sides, am i making this air tight by fully taping the polythene to the celotex or, just holding it in place?

Second question, the polythene is 4mx25 so obviously i need to tape it with poly tape, no problem i got some really sticky $ht! Do i need to go over the top and make 'waterproof' so to speak or just tape it and forget about it. I can see myself taping the hell out of it

Third question.. i will be putting expanding foam betweed the celotex butt joints, then sealing with foil tape so it will end up like a continuous board. Should i seal the exposed sides of the celotex at the perimiter or is this a nono?

Obviously im trying to keep the boards dry by going over the top on visqueen while not working on it. Should the rain get under at any point, will it work it's way out?

I really have searched on this but cant get definitive answers

It's a tricky point.

A VCL below the celetex means rain on top of the celetex will run down any gaps and get between the celetex and the the VCL.

I wouldn't use visqueen it's far too stiff for use as a VCL unless you have a simple flat rectangle.

Yes tape joints on the VCL, put down celetex, foam joints, use foil tape to seal upper layer.

ThrottleHappy · 21 Nov 2020

Thats what i was thinking. I will just stop if it starts raining then and put it on hold. Its supposed to be a dry day but we know how that ends up!

My main concern was trapping anything.

So the theory is that the vcl, and all board joins should be sealed so its its pretty much an airtight slab with a plastic bottom!

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Vcl laying method warm roof

ThrottleHappy

Notch7

ThrottleHappy

DIYnot Local

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