insulation on corrugated roof

baldric · 17-04-2018 07:24PM #1

HI , I have a question about spray foam an old corrugated roof.

an old residential building with timber joists in excellent condition in the corrugated roof, it has no attic or crawl space so living space is into the roof. The requirement is to spray foam, and on completion to batten out and tongue and groove the ceiling. The foam is required to prevent condensation and to insulate the roof space. I think I need:
----open celled?
----75mm?
----direct onto the corrugated, without card.

Is this reasonable is there anything else I am missing out on? Any useful tips, do I need to leave gaps at eves for air to penetrate, do I need to do anything to protect the timber? Is there any FIRE issue with this scary foam and use of timber tongue and groove?

thanks

baldric

buky · 24-10-2018 10:30PM

hi, can I ask how did you get on and what did you do in the end?

johneym · 01-04-2019 10:16PM

me too would love to hear back?

Calahonda52 · 02-04-2019 07:10AM

baldric wrote: »

HI , I have a question about spray foam an old corrugated roof.

an old residential building with timber joists in excellent condition in the corrugated roof, it has no attic or crawl space so living space is into the roof. The requirement is to spray foam, and on completion to batten out and tongue and groove the ceiling. The foam is required to prevent condensation and to insulate the roof space. I think I need:
----open celled?
----75mm?
----direct onto the corrugated, without card.

Is this reasonable is there anything else I am missing out on? Any useful tips, do I need to leave gaps at eves for air to penetrate, do I need to do anything to protect the timber? Is there any FIRE issue with this scary foam and use of timber tongue and groove?

thanks

baldric

A bit late now but its not the right construction.

The risk here is that the open cell will allow moisture through which will be absorbed by the timber and the timber will eventually rot as it wont be able to dry out.
https://wentzelheatingandair.com/insulation/spray-foam/faq/

baldric · 03-04-2019 08:06AM

Calahonda52 wrote: »

A bit late now but its not the right construction.

The risk here is that the open cell will allow moisture through which will be absorbed by the timber and the timber will eventually rot as it wont be able to dry out.
https://wentzelheatingandair.com/insulation/spray-foam/faq/

Caljonda. Thanks for reply, never did the job as couldn’t get any proper direction on
Fire and on how to deal with timbers issue, I would like to do it but I got conflicting answers from installers on
Everything!! One would say open
Cell is your only man
And the next would say closed cell and then I’d be told it was A rated for fire but there’s no actual cert....because it’s going through the certification!!!! Basically I don’t think they knew!!! Or cared. So I just forgot about it.

It looks the 2 other guys that asked on the forum would like to do it too... is there any fool
Proof fire rated solution to doing the job??? Any suggested spec you could give that we can go to an installer and say

We want ABCD in
underside of corrugated roof with timber joists and please give a quote ??

Looks like closed cell? And is there my prohibition to using in a domestic space?

Thanks for taking the time, Baldric

Calahonda52 · 03-04-2019 10:06AM

Please post some pictures of the current set up

baldric · 03-04-2019 05:38PM

Calahonda52 wrote: »

Please post some pictures of the current set up

Pretty simple 7 x 2’s holding up a corrugated tin roof

baldric · 03-04-2019 05:40PM

Calahonda52 wrote: »

Please post some pictures of the current set up

Pretty simple 7 x 2’s with corrugated tin...no membrane

my3cents · 03-04-2019 08:42PM

If you'd put some tyvek under those sheets just to stop the drips then you'd have had a lot more options but I don't think you need telling that.

baldric · 04-04-2019 09:31AM

my3cents wrote: »

If you'd put some tyvek under those sheets just to stop the drips then you'd have had a lot more options but I don't think you need telling that.[/quote

Roof already in place a long time...looks new but timbers replaced and treated where needed....I suppose could tyvek between joists and then cut polyiso but would be huge Time and effort compared to a spray which would be done in 2 hours and there will always be the gaps under the rafters after all that effort leaving drips on to wood....... I think spray only solution if can be made work

baldric · 04-04-2019 09:31AM

baldric wrote: »

my3cents wrote: »

If you'd put some tyvek under those sheets just to stop the drips then you'd have had a lot more options but I don't think you need telling that.[/quote

Roof already in place a long time...looks new but timbers replaced and treated where needed....I suppose could tyvek between joists and then cut polyiso but would be huge Time and effort compared to a spray which would be done in 2 hours and there will always be the gaps under the rafters after all that effort leaving drips on to wood....... I think spray only solution if can be made work

Between rafters not joists !!

my3cents · 04-04-2019 10:01AM

I'd spray the "tin" but not for the obvious reason.

The problem here is that whatever you do the tin is going to get very cold at night, collect all the moisture and dump it on whatever is below in the morning. I'd put a thin say 10-20mm layer of spray foam on the tin to prevent that. At the same time I'd make sure the eves were open to allow ventilation up and over the inside of the roof to help keep the whole underside of the structure dry.

Once that is done you can put your insulation on the rafters underneath. I wouldn't put anything between the rafters because thats where you want some air flow to keep everything dry.

I'm sure thats 200% against every building reg anyone can look up but a tin roof isn't a good starting point to be complying with modern regs so you just do what you can in a way that will last as long as possible. A thin layer or spray foam isn't going to affect the wood much and the ventilation will help keep it dry anyway.

insulation on corrugated roof

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