Spray foam insulation

[Temp]

From my news feed

 

https://inews.co.uk/inews-lifestyle/money/mortgages-equity-release-warning-over-loft-insulation-that-could-make-homes-worthless-1402136

 

Hundreds of thousands of homeowners who had spray foam installed in their lofts could find their properties are worthless unless they spend thousands of pounds having it removed.

 

Snip

 

There are two types of spray foam insulation, open cell spray foam insulation and closed cell spray foam.

The issue is with the closed cell spray foam, said Mr Wilson. “Because it seals the roof space with this material, air circulation can be restricted to the roof and timbers. This can lead to condensation, which in turn can eventually lead to the rotting of the wooden roof supports.”

[Radian]

I read that in my feed too. Reminds me of my concerns about Aldi's special on vapour barrier insulation:

 

 

Similar issue but at least the foil can easily be removed if it does cause a problem. I can't get my head around how any timber structure can be wrapped in a non-breathable covering - unless it can be guaranteed to form a continuous vapour barrier around it - but is even that safe? ?

[ProDave]

You see this on housing forums where a surveyor has marked a building down because of it.  I believe the big complaints are they cannot inspect the state of the roof structure and in cases where there is no felt on old houses, the foam will be stuck to the back of the tiles making a roof repair very much more difficult.

 

the notion that it makes the property £0 value is absurd.  I would like to find one if these and would hapily buy it for £0.  Surely at worst it would down value the house by the cost of a re roof?

[saveasteading]

Foam insulation is horrible, and could cause problems, but the house is not worthless.

Superfoil appears to be overhyped but is a quick improvement for some situations (attic, garden shed). It does not 'wrap' any timber and it can usually breathe on the other side.

The Aldi pic is an unheated attic. so for storage that won't cause much issue, but if turned into  sneaky occupied room it could be a big problem.

[SteamyTea]

Surely all that has to be done us to externally render, or internally plaster, the area with lime.

Everyone says it cures all the damp issues. Well apart from actually curing itself.

 

(Just taking the piss after a 5 and a half hour car journey where I had too much time to think about things)

[Radian]

1 hour ago, saveasteading said:

Superfoil appears to be overhyped but is a quick improvement for some situations (attic, garden shed). It does not 'wrap' any timber and it can usually breathe on the other side

 

I'm not so sure. Most pre 21st century houses have Bituminous roofing felt which doesn't breath so without crossflow there's scope for rot. But I wasn't thinking so much of the rafters above but the attic floor/ceiling below. A house worth of water vapour is waiting underneath and a fully foiled-up attic suddenly becomes unventilated for the first time in the houses history - unless a deliberate Vapour barrier exists at ceiling level. Again, ventilated attics never had such a fitment. IMO, Interstitial condensation is not something your typical Aldi customer has at the forefront of their mind.

[scottishjohn]

surely the answer is to foam between rafters and leave edge of rafters exposed allowing viewing and breathing of the wood  and no one is going to fill rafters up too the top anyway with closed cell -too expensive and no  need

 and on anther note how would a building surveyor when checking a house with modern insulated  vaulted ceilings check the condition of the roof-

they cannot so same should apply to them 

Edited January 16, 2022 by scottishjohn

[scottishjohn]

19 hours ago, Temp said:

The issue is with the closed cell spray foam, said Mr Wilson. “Because it seals the roof space with this material, air circulation can be restricted to the roof and timbers. This can lead to condensation, which in turn can eventually lead to the rotting of the wooden roof supports.”

and this isi a load of crap 

yes closed cell will not pass water and it is stuck to sarking   so obviously there can be no condensation on sarking or osb sheeting - and if its a cold roof there should be ventilation at the eaves and or up the cavity wall 

your batons and roof paper on top of sarking gives ventilation to outside anyway 

 read the small print in any house survey and it will exclude any areas that cannot be seen without dis mantling any thing 

Edited January 16, 2022 by scottishjohn

[Radian]

1 hour ago, scottishjohn said:

yes closed cell will not pass water and it is stuck to sarking   so obviously there can be no condensation on sarking or osb sheeting - and if its a cold roof there should be ventilation at the eaves and or up the cavity wall 

 

Surely there's no point at all in spraying foam in what will remain a cold roof loft? The intention must be to convert it into an unventilated, warm roof.

 

If the house was constructed with a warm roof at the outset then, as you point out, a surveyor couldn't inspect the condition of the roof covering from the inside anyway. So what nonsense is it then to deter the conversion of a cold roof into a warm roof on the grounds that it couldn't be inspected alone?

 

However I think it's not entirely trivial to analyse the outcome of such a conversion... In a modern attic room with a cold roof, insulation is typically located between the rafters in addition to a continuous layer on the back of the rafters to ameliorate cold bridging. A vapour barrier is then required on the inside between the insulation and internal finish e.g. plasterboard with a foil backing. so far so good as all this can all be done as a retrofit. But the wind control layer under the outside roof finish always seems to be specified as vapour permeable (to provide ventilation for the timber rafters) and the insulation would be prevented from going all the way to the outer face of the rafters to promote air circulation for the timbers. This, I understand, is standard practice for a cold roof attic room.

 

So this is where I get a bit lost with the closed cell spray foam because if the original wind control layer was a vapour barrier (Bituminous roofing felt, sarking etc) then the rafters should not be subject to water vapour at all and, I guess, would be fully sealed (my instincts tell me this is bad though). The build-up on the outside of the wind control layer is no different to before the conversion so that's fine. The back of the rafters on the inside would still be a cold bridge but for the fact that the spray foam covers them completely so that should be OK as well. I personally wouldn't want there to be a void between rafters (given that the foam will not fill the space entirely) so I would fill with rockwool or similar -  even though the void should remain warm and dry. Seems like the application of closed cell spray foam should be OK then ? ?

[Temp]

With spray foam you get an unventilated cold roof (eg structural members, or at least part of them, on the cold side of the insulation). Normally Building Control won't allow this if you are building a new house. It must be warm roof (insulation above rafters) or ventilated (normally 50mm air gap). But for some reason it's acceptable when it's spray foam.