Can someone explain the mechanism how the foam can damage the building? I didn’t quite get it from the article.
> Executive found that condensation could cause 25% of roof timber to decay within five years if spray foam is applied directly to roof tiles, or certain underlays. The general risks increase the further north the property is, because of colder climates.
Most houses in the UK will have a timber frame, condensation will cause the wood to rot.
All that being common knowledge, it does indeed seem weird that people were just spraying foam directly on the inside of their roofs as vapor will be deposited somewhere in the open cell structure of the foam, or against the inside of the wood/roof-tiles (as the air cools down, it can hold less and less water so that condenses).
Given all that knowledge, I'm still unable to close all the vapor bridges in my house, because I can't remove certain structures. So it is still a bit of a gamble here and there, where the moisture will pile up. I just try to get it to pile up in sites that are exposed to outside air.
I can't imaging everyone being as analytical and careful as me though. Indeed I sometime here people just pasting PIR plates or mineral-wool in place and leaving them like that, no vapor screens or anything. Time will tell what happens to these houses. Old houses were made to just have a lot of heat-transport through the structure, which prevents vapor deposition. Insulating any house should come with at least some thought about where the humid inside air will go (preferably outside through ventilation holes.)
When using any type of insulation in places where temperatures can vary and humidity can get high you should always ensure the wooden parts have enough room to breathe (e.g. 10cm of empty space above them if the insulation is at the bottom).
The above is my current belief. Who knows if I'm right.
Also if you want insulate an old house consider you should install an HVAC system so that you are properly venting. Old houses self ventilate because they’re so loose compared to modern homes with tight envelopes.
Closed cell foam insulation is a vapor barrier, which is where the problem comes from. You must never have two vapor barriers as any moisture that is between them cannot get out and this will cause mold and rot.
Punching a small hole in a wall and putting foam is fine so long as the foam and the existing vapor barrier are touching each other and thus form one barrier. However if there is something between the vapor barrier and the foam you have two barriers and problems.
>A report published in March by the government’s Health and Safety Executive found that condensation could cause 25% of roof timber to decay within five years if spray foam is applied directly to roof tiles, or certain underlays. The general risks increase the further north the property is, because of colder climates.