> 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.
I was wondering indeed, I am insulating with PIR plates, but they are coated with a vapor-closed layer and one is advised to tape all panels together with vaper-closed (aluminum) tape, so no air from inside the living area can get into the insulating layer, cool down and leave condensed water. As an additional precaution, the advice is to not insulate from the inside if a vapor-closed foil is on the outside of the wooden part of the roof (where the tiles are resting on), to ensure any vapor getting into the insulation after all, can vaporize away when temperatures rise.
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.)
It’s basically the same thing as wrapping the wood into a plastic bag. When water condenses inside the plastic it has no way of escaping and starts to rot/mold the wood.
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).
After thinking about this a while (and contradicting my previous reply, though I want to leave it as it is generally correct!) I think this isn't about vapor or condensation at all. I think this is about leaky roofs! If your roof leaks, rain water gets on the wood, and the foam traps it there (even open cell is slow to wick it away) and so it rots the wood away. Worse, since there is no drops inside the homeowner has no warning that things are going wrong and so won't call a roofer to get the issue fixed. (roofers also are not perfect and so if the new roof leaks they won't know to do warranty repairs before the beams fail - in a normal house you notice the drip, and fix the problem before anything bad happens)
The above is my current belief. Who knows if I'm right.
Water vapor condenses into water and causes mold/rot. Closed cell foam doesn't let water out through the foam (open cell does, but open cell vs closed cell needs a long discussion of pros and cons - in general I'd call closed cell better if you can mitigate this issue). The problem is insulation is added in summer when there is high humidity (there is a minimum temperature) so all the wood is at the wetter stage, then winter comes and the whole wall cools off and any air trapped condenses the water since the water vapor cannot escape.
It traps moisture which leads to mold and for wood to rot. You nearly never want to install insulation without a vapor barrier. And especially not with spray foam. People do it because it’s cheap to do. You only have to punch a small hole in the wall and spray into it.
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.
> You nearly never want to install insulation without a vapor barrier. And especially not with spray foam
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.
When applying insulation from the inside, the walls and roof will be cool during the winter. If warm air (which can hold a lot of water) somehow leaks through the insulation, it will cool down. Cool air can hold a lot less water, so the water gets released into the structure. A wooden ceiling can rot away quite quickly if it is constantly moist.
I believe the actual issue the article implied was it prevents inspection of the roof lumber in addition to moisture trapping. Since a mortgage company can’t see the lumber and framing they won’t mortgage it. Thus you can’t sell the home to someone mortgaging it.
Moisture management is the largest risk I know of with foam.
Of course ideally the wood holding up your house or roof never gets wet, but if it does it's not an existential threat, unless it stays wet. Foam doesn't allow the wood to dry, and that can cause rot. Rot, if it's enough members can cause structural problems.
>But because surveyors are unable to inspect the roof timbers behind the layers, mortgage lenders tend to issue blanket refusals on properties where any foam is present.
I assume that it's due to the expanding nature of the foam -- they are afraid that the foam might continue to push against the roof timber and crack it I think
No they specifically mentioned condensation and how it affects properties in colder climates more. I think they're afraid the improperly installed insulation will allow condensation to build up below the roof timber which will cause the timber to become wet and degrade.
>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.
