[CyberDildonics]

You are completely right, a lot doesn't add up. People in this thread seem to just accept the moisture argument without thinking it through or doing research. Lots of people have spray foam and lots of people are happy with it. There is no '25% of wood deteriorating over the next couple of years'.

The reason it's nonsense is that the side covered with foam (especially closed cell) is now protected by waterproof polyurethane. Water isn't getting to that side.

The other side is now insulated from the inside, so that isn't getting things like condensation because the temperature differences should be negligible. If people think about a cheap styrofoam cooler, it's cold on the inside and there isn't condensation on the outside on a humid summer day. The outside isn't cold, that's the point, so condensation doesn't happen there.

Then maybe someone would say if there was a roof leak the wood would get wet and rot, but that would happen anyway. That's a major disaster and foam won't cause any more problems than are already happening.

[lm28469]

Water _will_ get through your roof at some point, and it'll sit nice and tight right above your spray foam, for years, decades, and you'll never ever know about it until the problem is too big to handle.

This is especially true for hack jobs on older buildings.

[arethuza]

Whereas the traditional warning sign in older UK buildings is for you to know about a problem with your roof by having your ceiling plaster collapse when you least expect it!

[lm28469]

Jokes aside you don't usually plaster the inside of an attic, unless it's a liveable attic, but that's far from the norm.

A lot of people spray foam in old attics as a set and forget insulation measure: https://www.stellrr.com/wp-content/uploads/2021/04/AAF45418-...

[arethuza]

I wasn't joking - I've been in two top floor flats in the UK in older buildings (central Edinburgh) that had ceiling plaster collapse due to roof problems.

[CyberDildonics]

Why would water be able to get through your roof but air not be able to get to it at the same time?

Why would water be able to get through your roof with spray foam making anything worse? Water damage means you have to replace things anyway.

[lm28469]

> Why would water be able to get through your roof with spray foam making anything worse?

Because your roof _will_ fail, they all do, once it does the water will collect between the roof and the foam, because while it's not air tight there will be nowhere near enough ventilation do get rid of it

> Water damage means you have to replace things anyway.

Yes, but if your entire wooden structure rots for 5 years because you didn't detected the leak since it's hidden behind 20cm of foam you are utterly fucked.

It's well documented, feel free to google it if you don't believe me.

https://sprayfoamreclaim.com/wp-content/uploads/2022/10/PHOT...

[CyberDildonics]

Because your roof _will_ fail

You said that already but it doesn't answer any of the questions I asked. Repetition doesn't make something true. There are typically shingles, then a layer underneath, then wood sheathing like OSB. All that is for the cheapest roof.

https://diy.stackexchange.com/questions/32820/is-it-ok-for-o...

once it does the water will collect between the roof and the foam

Says who? If water is getting to the wood, why isn't air getting to it? Typical roofs last for 20-30 years.

This idea that foam is bad because seeing water soak through through the entire wood sheathing is nonsense. This is also only dealing with foam on the underside of the roof, which is also not the only place or way it can be used.

but if your entire wooden structure rots for 5 years

Now your "entire wood structure" is going to rot? If you want to know if there is moisture in your wood, go in your attic. This idea that roofs blow off without anyone noticing and huge amounts of water soak all the wood in a house and the entire thing rots without any indication is not reality.

feel free to google it if you don't believe me.

You can feel free to google it because you're the one making the claims.

[Jensson]

> Water _will_ get through your roof at some point

Why? It isn't like water will get through metal plates, at least not within many decades.

[lm28469]

Not all roofs are "metal plates", most aren't actually. Either way some roofing materials are rated for as low as 20 years, depending on the climate and how good they were installed they might fail earlier

You'll always have a failing shingle/tile here and there, unless you plan on inspecting the whole structure under the foam every year you could very well miss it for many years.

A puddle in the attic or a wet rock/sheepwool panel will be much easier to discover/fix. A small leak under 20cm of sprayed foam will be a nightmare to locate

https://www.24-7pressrelease.com/press-release/488240/homeow...