I was called in to look at some problems in a community hall. Their wooden floor on joists had gone spongy and been taken up to reveal a load of cellar fungus between the vinyl and 1/8” ply sheet underlay.

I am strongly suspicious that as they hadn’t been using the building much this winter and as it was empty with no heating on that on a lot of occasions the inside was colder than it was outside. Now with air being able to flow in to the under floor void from outside and that air holding enough moisture for it to condense on the underside of the vinyl as this was below the dew point of the incoming air as the room was cold, wetting the ply and growing moulds.

Very fortunately this hadn’t turned into dry rot but I am sure that it would have in time.

There were no plumbing leaks and the subfloor void was dry where exposed vaguely damp under ant detritus down there.

Any view or common experience

Ice inside cars forms on windows that super-cool by radiation to the clear sky on a winter night, to be much colder than the air temperature. We sometimes get the same on the underside of a steel roof on an outbuilding. Don't see how that can happen under a floor?

Tony is there any sign that the vinyl was glued down, eg with some compound that has attracted mould?

Is the fungus specifically inbetween the vinyl and the ply, or is the ply itself gone mushy?

When the floor went "spongy", does that mean the joists have rotted, or just the ply? Guess there are some floorboards/chipboard between the joists and the ply, are they rotted?

I like the topic title - such troubled times!

The formation of ice inside cars depends entirely on how much moisture there is in the internal air.

And how many times is there ice on the inside after you ventilate before closing it?

We fairly frequently have ice inside the windscreen if it has been a clear starry night, say from December to February.

If you've ever driven in a Northern climate, you know you have to have the blowers on the whole time in Winter so a) you can see out and b) you don't shiver, so the car is always well ventilated before you close it.

A good proportion of people who move here from down South only last a couple of years, it's not a very pleasant winter climate for those of us who didn't grow up here. But the Summer is much better, long daylight and no overheating!

I have a suggestion. Instead of 'discussing' the theory of ice on car windscreens forever, why not conduct an experiment? Next time conditions are suitable, just try my proposal of opening the windows whilst driving home, so the air in the car is fresh and cold when you leave the car.