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Important info not in title or body of post: Mortgage companies are worried that spray foam can cause condensation which damages timbers.
Just to clarify further: Condensation management as part of insulation is half the battle, but frequently overlooked.
The problem comes where cold surfaces meet warm air, and what happens to the moisture in the air at that point.
The spray foam seals the timber in a way that it cannot be accessed from the inside, but generally a membrane in not installed on top of the wood. So warm air can still get through.
If my room is full of lovely 21 degree air, and the outside is zero, then if that air is able to get to a nice cold roof truss, it will be dropping a lot of evaporated water on the truss.
And if that wood can't get sufficient airflow to dry out, it'll get damp. And eventually rot.
Meanwhile, you can't even get to the truss to look at it, because it's covered in foam.
So the mortgaging companies are (very understandably) staying away from that potential hot potato.
You could have a house that looks absolutely fine, until the trusses start collapsing.
The ways we work around it are either ventilation (having the roof itself still vented to the outside), vapour sealing (stopping warm air from getting to the insulation), or using ventilation that breathes (water/vapour can move through it, allowing it to dry out naturally).
Can someone explain why spray foam seems to be the go-to for US construction? Is it different types of wood/treated vs untreated?
"At the root of the problem are cowboy traders (unlicensed tradesman/contractor) 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." also "because surveyors are unable to inspect the roof timbers behind the layers [for moisture], mortgage lenders tend to issue blanket refusals on properties where any foam is present." Maybe in the U.S. we just use wood moisture meters to check for moisture?
My impression is that homes in the US tend to have more wood involved in their construction generally, so it seems plausible to me that US construction methods may be more experienced with ways of managing wood moisture
Sounds like the foam is the issue, which may be down to the shade tree handy man they hired being unlicensed or uninsured to perform insulating. If a person isn't a dedicated HVAC worker who has day-to-day experience with insulation types and how to properly apply them, then the work may be causing more harm than good.
If the insurance and mortgage companies have a list of guidelines needed for insulation installation, it makes sense that folks need to follow them to continue using their services. Spraying any old foam into nooks and crannies is a fine way of hiding problems.
The problem with this style of foam application, is that you cannot get to the wood to check the moisture content, without ripping down the foam (or probing through it, exacerbating any problem).
So there isn't a way to test. And as there have been problems, the lenders won't take the risk on any more.
I was thinking the meters with the metal probes that go through yeah. Wasn't aware that could exacerbate the issue.