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Interesting the difference between UK and USA here. Spray foam applied directly underneath the roof deck is very common here and is a recommended assembly by bu

Interesting the difference between UK and USA here. Spray foam applied directly underneath the roof deck is very common here and is a recommended assembly by building scientists, e.g. https://buildingscience.com/documents/digests/bsd-149-unvented-roof-assemblies-for-all-climates https://buildingscience.com/documents/digests/bsd-149-unvent... Not sure if there is a significant climate difference in the UK that makes this construction more problematic, the article mentions moisture but the U.S. building scientists say 2 inches closed cell spray foam will block air and vapors from reaching the wood of the roof. Perhaps the issue is the open cell foam mentioned in the article - it seems that closed cell foam is the recommended type in the USA.

CyberDildonics 2y ago
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 2y ago
  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 2y ago
    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 2y ago
      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/AAF45418-1CB5-49E4-98B5-274BD78916B1-scaled.jpeg https://www.stellrr.com/wp-content/uploads/2021/04/AAF45418-...
      - arethuza 2y ago
        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.
  - Jensson 2y ago
    > 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 2y ago
      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/homeowners-consumer-center-discovers-a-major-issue-with-spray-foam-insulation-in-new-home-construction-it-may-encapsulate-water-from-roof-window-leaks-so-a-homeowner-is-unaware-of-the-problem https://www.24-7pressrelease.com/press-release/488240/homeow...
arethuza 2y ago
It might be because slate/tile roofs are the most common roofing materials used in the UK and insulation is usually (in my experience) laid between the joists?
throw0101d 2y ago
> Not sure if there is a significant climate difference in the UK that makes this construction more problematic, the article mentions moisture but the U.S. building scientists say 2 inches closed cell spray foam will block air and vapors from reaching the wood of the roof. Perhaps the issue is the open cell foam mentioned in the article - it seems that closed cell foam is the recommended type in the USA. Implementation details matter. From the OP's article: > At the root of the problem are cowboy traders who apply the foam without a full survey or appropriate expertise – but because of lenders’ caution, this is affecting other homeowners who had similar work. One potential problem that could occur is ridge rot: > Lots of attics insulated with open cell low density spray foam (Photograph 1, Photograph 2 and Photograph 3) are having problems – in hot humid climates, mixed humid climates, and cold climates. The problems are moisture related. The attics are “unvented” – open cell low density spray foam is installed directly on the underside of roof sheathing. The attics are humid. Very humid. Unacceptably humid. And the humidity collects at the upper portion of the attics. * https://buildingscience.com/documents/building-science-insights-newsletters/bsi-016-ping-pong-water-and-chemical-engineer https://buildingscience.com/documents/building-science-insig... > When you spray ocSPF into wall cavities from the interior the ocSPF can act as the air control layer and thermal control layer. It can’t act as the vapor control layer – it is too vapor open. This is a problem when you spray ocSPF on the underside of roof/attic assemblies you can end up with problems (“Ping Pong Water”). * https://buildingscience.com/documents/building-science-insights/bsi-126-dirty-harry-does-insulation https://buildingscience.com/documents/building-science-insig...

CyberDildonics 2y ago

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 2y ago
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 2y ago
  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 2y ago
    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/AAF45418-1CB5-49E4-98B5-274BD78916B1-scaled.jpeg https://www.stellrr.com/wp-content/uploads/2021/04/AAF45418-...
    - arethuza 2y ago
      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.
- Jensson 2y ago
  > 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 2y ago
    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/homeowners-consumer-center-discovers-a-major-issue-with-spray-foam-insulation-in-new-home-construction-it-may-encapsulate-water-from-roof-window-leaks-so-a-homeowner-is-unaware-of-the-problem https://www.24-7pressrelease.com/press-release/488240/homeow...

arethuza 2y ago

It might be because slate/tile roofs are the most common roofing materials used in the UK and insulation is usually (in my experience) laid between the joists?

throw0101d 2y ago

> Not sure if there is a significant climate difference in the UK that makes this construction more problematic, the article mentions moisture but the U.S. building scientists say 2 inches closed cell spray foam will block air and vapors from reaching the wood of the roof. Perhaps the issue is the open cell foam mentioned in the article - it seems that closed cell foam is the recommended type in the USA. Implementation details matter. From the OP's article: > At the root of the problem are cowboy traders who apply the foam without a full survey or appropriate expertise – but because of lenders’ caution, this is affecting other homeowners who had similar work. One potential problem that could occur is ridge rot: > Lots of attics insulated with open cell low density spray foam (Photograph 1, Photograph 2 and Photograph 3) are having problems – in hot humid climates, mixed humid climates, and cold climates. The problems are moisture related. The attics are “unvented” – open cell low density spray foam is installed directly on the underside of roof sheathing. The attics are humid. Very humid. Unacceptably humid. And the humidity collects at the upper portion of the attics. * https://buildingscience.com/documents/building-science-insights-newsletters/bsi-016-ping-pong-water-and-chemical-engineer https://buildingscience.com/documents/building-science-insig... > When you spray ocSPF into wall cavities from the interior the ocSPF can act as the air control layer and thermal control layer. It can’t act as the vapor control layer – it is too vapor open. This is a problem when you spray ocSPF on the underside of roof/attic assemblies you can end up with problems (“Ping Pong Water”). * https://buildingscience.com/documents/building-science-insights/bsi-126-dirty-harry-does-insulation https://buildingscience.com/documents/building-science-insig...