Spray foam UNDER gf floorboards - an issue?

[Duvetstealer24]

I've been reading about the issues around getting a mortgage on homes with spray foam insulation in the loft. We don't have this but did get foam sprayed under the floorboards of our home on the ground floor, as it is suspended. The idea was to insulate it from the colder air below and it was done by a little robot!
Husband said because the air is colder below the house it isn't the same issue as roof sprayed insulation.
Any idea how I can check a) if there are any problems with it (I don't want to lift floorboards because that will break the foam seal and more likely cause problems) and b) whether this is also a problem for selling on later? We might well move in a few years.

We are doing an extension and about to put new flooring in around the whole downstairs, including over the wooden floorboards. So if we DO need to remove the foam spray (goodness knows how!) then it needs doing sooner rather than later. It may be totally fine... but not sure how to check. Thanks!

Google suggests it may be an issue.

https://www.mortgagesolutions.co.uk/news/2022/05/25/advertised-sub-floor-spray-foam-insulation-responsible-for-unmortgageable-homes-rpsa/

I would think the same as it’s timber that’s can’t breathe

Yes...but then the RSPA retracted that later... not sure however what the latest view is! I do wish we hadn't done it but it's too late for that now, so it's a question of how to work out if it is causing any damage or not.
https://www.mortgagesolutions.co.uk/news/2022/10/27/rpsa-retracts-spray-foam-guidance-pending-review/

But apparently the issue is moist air. Moist warm air rises in a house so it's a problem in lofts. Below the house is cold dry air so - I'm told - there isn't a problem with breathability.

I'm interested in this as it an ideal solution for my own suspended wooden floor. As the boards are stripped and stained I'd rather not have to lift them for other methods. However, I will at some point be selling the house.

I did a bit of googling on it and couldn't get a definitive answer. It seemed it was just lumped together with spray foaming of roofs.

Given that you have airbricks creating a cross flow under suspended floors, I'd say it unlikely they'd be completely dry so moisture issues could still apply.

I have just read my advice over and I sound awful, I'm so sorry, it's just that I would be gutted to spend all the money, live through all the chaos then sit in your lovely new extension only to find you have to rip up the floors and replace everything because something like a tiny leak inside the wall or a heavy rainstorm got as far as the wood (from above or below) and meant you had to pay thousands and live with the chaos again. The floorboards may be sealed but joists go into walls where the robot can't spray.

It's kind of a disaster wherever you put it. Ventilation under your house is really important as it prevents damp and means any water can evaporate (even at really cold temperatures).
Most people counteract the cold by putting carpet and underlay down to stop the draughts, and if you are putting something on top of the boards you will be making it much better anyway (without the spray foam). The foam traps any moisture next to or into the wood and they will rot. So you will have rotted joists as well as floorboards.

There are actually some really clever underfloor insulation solutions that can be DIY if you are handy, like making a chicken wire cage with at least an inch from each joist and filling it with something like Thermafleece or hemp insulation (only suggesting them because they also allow any damp to evaporate and are natural as opposed to the spray foam which is an environmental horror story for the future).

I would think that perhaps the mortgage company wouldn't explicitly point it out, as I have never heard of anyone doing it, but once they know people do, it will get more explicit. It causes the same problem, rotting wood which you won't be able to see because there is foam everywhere. It's just that instead of a new roof, you would need new joists and floorboards throughout, new flooring and the walls fixed (because water does not simply go away it will find a way round and if it can't evaporate or drain out it will go up the walls and the cold is MUCH colder in a damp house. Also if you live in a house pre 1910, you absolutely should not put in a damp proof course - often mortgage providers say one is needed but if you explain you are in an older house they should waive the condition. DPCs just trap damp below the course, once you plaster it takes a while to leach through so you think it must be something new going wrong.

I think your best bet would be to have the foam removed now, unblock the air vents (inside and out) to let air through before you put your lovely new extension on. That way you won't suddenly notice that your floor is unexpectedly springy because there is nothing holding it up.

The idea with a suspended timber floor is that there is a cross-flow ventilated (with air bricks) void beneath it to prevent the air in the void becoming too humid. If it is too humid, depending on the humidity level and temperature, either wet rot or dry rot of the timbers could occur.

Interesting @Knickersinatwist36 @HoppyFish . Have either of you encountered situations where spray foam has actually damaged a floor by causing or accelerating rot?

I am also wondering if the underfloor system uses open cell foam which in theory ought to allow wood that was damp, to dry out to the ventilated floor space below or closed cell which could indeed cause moisture to become trapped.

I’ve never encountered a floor insulated with foam, I don’t think it’s very common?

Oh, I’ve just discovered that spray foam can be used as retrofit insulation in timber suspended floor. Everything is explained in page 35 of this document. It mentions that the foam should not touch the ground etc:
assets.publishing.service.gov.uk/media/5f05d211d3bf7f2be6e0217a/suspended-timber-floors-underfloor-insulation-best-practice.pdf

It is closed cell foam in this case. Although technically there shouldn't be any water or moisture entering between the foam and the wood, as it is sealed.

I think the issue as I think a pp suggested might be at joist ends where they sit in a potentially cool or damp wall fooring or basement wall. However as the timber itself is on the warm side of the insulation this might not be an issue. I expect the system suppliers have done some research into potential moisture issues. Did you get a warranty? I know this makes a difference to some lenders with the roof stuff (ie they will lend if there is a warranty, not if there isn't)

Spray foam or anything else under the floor is going to affect the balance of moisture under there. Especially older houses rely on that balance to stay in good condition, so water is lost as quickly as it gathers.
If a floor is doubtful already then spray foam would definitely exacerbate things, but I assume (!) they did a proper survey before putting it in.
Our floor 1920s house was in a right state even without insulation due to hearths, water coming down the chimney, slate DPCs, and damp walls. First task for me was to pull things up and replace any rotten wood, then remove any possibility of water buildup, and finally insulate it all. If I'd skipped the first steps then it would be a right state.