Spay foam under pitched roofs

[Radian]

In this other thread...

 

The subject of having to rip out spray foam from a property that was bought at auction reminded me of a story that keeps cropping up in tabloids - people who had 'cowboy installers' spray their attics and find that their property becomes unsellable because buyers can't get Mortgage Companies to lend on account of a perceived problem. How justified are their concerns?

[Iceverge]

A friend of mine had it done on his new build about 10 years ago. 

 

No complaints. 

[Radian]

The story seems to be that surveyors cannot examine the condition of the rafters. Which is exactly the same for all room-in-roof conversions with insulated, plaster boarded ceilings. I suspect that the excuse is that there is no traceability in the installation process where evidence of an initial examination of the condition of rafters and build-up to external roof covering (felt etc.) prior to installation might not be available. However, I would be unable to provide evidence for that in my recent RIR conversion either. Who knows what's above such a ceiling in attic rooms?

Edited April 23, 2022 by Radian

[Roger440]

The real problem is that the timber rots. But you cant see that until its too late.

 

If i was buying a house with that done to a conventional roof, id by budgeting for a new one.

[RobLe]

Modern roofs have a breathable membranes under the tiles, while older ones will have a non breathable one.  Does that make a difference for how likely the timbers are to rot?

[Temp]

11 minutes ago, RobLe said:

Modern roofs have a breathable membranes under the tiles, while older ones will have a non breathable one.  Does that make a difference for how likely the timbers are to rot?

 

Yes. In theory you don't need a ventilated void if its a breathable membrane. But the void is also to allow the membrane to drape.   If you push it against the underside of the batten dirt can accumulate and form a mud that stops water running down. A pool of water can form causing the batten to rot.

[MikeSharp01]

How does this situation work with full filled rafter builds - like ours which are 300mm deep and will very shortly be filled with warmcell then battened over and plaster boarded to create the vaulted ceilings, so none of our rafters will be inspectable either?

[ProDave]

9 hours ago, Roger440 said:

The real problem is that the timber rots. But you cant see that until its too late.

 

If i was buying a house with that done to a conventional roof, id by budgeting for a new one.

And part of the problem has been created by some of the installers who actually market this product as a way to patch up an old roof effectively "sticking" the tiles in place so they won't slip.

[ProDave]

1 hour ago, MikeSharp01 said:

How does this situation work with full filled rafter builds - like ours which are 300mm deep and will very shortly be filled with warmcell then battened over and plaster boarded to create the vaulted ceilings, so none of our rafters will be inspectable either?

My experience has been a surveyor will only note and comment on what he sees. so room in roof, which is common here, unless the walls are showing damp then they just make an assumption about what is behind them.

 

The difference between a new build with this spray foam and an old house, is you can be more certain a new build has been done properly with for example a sarking board and appropriate membranes so the foam is not in contact with the underside of the tiles. 

[Radian]

I think the typical application that concerns mortgage lenders is when spray foam is applied under old Bituminous Felt. The non-breathable felt would originally have risked condensation build-up on it (and the adjacent timbers) were it not for good ventilation from the eaves. But is it a mistake to assume that cutting off this ventilation by encapsulating the felt and adjacent timber is going to cause rot?

 

Condensation will occur at the location of the dew-point - which in turn is a function of the RH and temperature of the air at that location. If it is located within the actual insulation which is non air-permeable (closed cell) then I don't understand how there is any risk. (I'm not even clear about open cell insulation in this regard).

 

[joe90]

2 hours ago, ProDave said:

My experience has been a surveyor will only note and comment on what he sees.

Yes, my mate bought a bungalow, paid for a comprehensive survey then after moving in he fell through the bedroom floor and it was full of woodworm, turned out the whole ground floor was riddled and he had to replace the lot, joists and all. Survey company said they were not allowed to lift carpets so we’re not liable 🤷‍♂️.

[ProDave]

35 minutes ago, joe90 said:

Yes, my mate bought a bungalow, paid for a comprehensive survey then after moving in he fell through the bedroom floor and it was full of woodworm, turned out the whole ground floor was riddled and he had to replace the lot, joists and all. Survey company said they were not allowed to lift carpets so we’re not liable 🤷‍♂️.

The moral of that story is when viewing as house, go the the middle of each room and jump up and down......

[MikeSharp01]

11 minutes ago, ProDave said:

The moral of that story is when viewing as house, go the the middle of each room and jump up and down......

NO - "The moral of that story is when viewing as house, get the current owner to go to the the middle of each room and jump up and down......"

[willbish]

5 hours ago, Radian said:

Condensation will occur at the location of the dew-point - which in turn is a function of the RH and temperature of the air at that location. If it is located within the actual insulation which is non air-permeable (closed cell) then I don't understand how there is any risk. (I'm not even clear about open cell insulation in this regard).

Closed cell is the premium upgrade. Icyene basic offering is open cell 

[SteamyTea]

7 hours ago, Radian said:

Condensation will occur at the location of the dew-point

That is the starting point.

Once liquid, it can seep to many places, even travel uphill a bit.