Condensation in loft of empty house

[Str3bor]

I'm at a loss and wondered if anyone could help?

I moved out of my house last year, the house has been up for sale and I have agreed a sale, since I have moved out wet patches have appeared on the bedroom ceilings. I have had a roofer out who has said there doesn't appear to be any problems with the roof, there are no slipped tiles and the pointing on the ridge tiles is fine. The only visible issue outside was that the gutters were full of moss. Just to note the pitch of the roof forms part of the bedroom ceilings with the gutters sitting just above the window externally.

However, when you go into the loft all the joists are completely wet and there are damp patches on the floor, it appears to be condensation. The buyers are now saying a new roof is required but the survey they had done did not pick up any issues with the roof, nor did my roofer.

Since I have moved out there is obviously no heating on and no air flow throughout the house, I have also emptied the loft of a lot of things that were stored up there (there are still a few things left but not much). I'm not aware that there are any air vents in the roof and to be honest I wouldn't know where to find them. The roof is the original 1930s clay tile with no felt lining. The loft has insulation but the hatch doesn't but given this was never an issue until I moved out I'm not sure this is relevant.

Is there anything I can do to get rid of the condensation so the buyers don't try and knock money off for a new roof? I have had the gutters cleared and just wondered if there is anything else I can do? Heating on, windows open where I can etc? This was never an issue when I lived in the house and just seems to have happened since it became vacant.

Is there any condensation on the attic hatch? Reads to me like you’ve got some form of attic rain happening. You’re probably going to have to increase the insulation, put vents in or both.

One possibility is your house may be well sealed. Warm air from the summer can hold much more water than cold air in the winter. So maybe what has happened is due to lack of ventilation the humidity built up over the summer has condensed in the loft. It does seem to imply there is a lack of ventilation in the loft. Maybe because the insulation has been placed right up to the edges of the loft space blocking the vents ?

Another possibility is that you have something in your house that is making it very humid. A leak somewhere and that humdity is condensing in the loft as the coldest place.

Another possibility is that you have something venting humidity into the loft, an extractor fan, although if you haven't been living there this is less likely. And finally there is the possibility that if your house is a semi humidity is making it through the party wall into the loft if your neighbours house is very humid and warmer. Often the divisions between lofts in older houses are not as well built as newer ones.

I would have thought a dehumidifier in the loft and the house should enable you to suck out all the humidity. if I was a buyer though I would not be happy until I found out what exactly was causing the humidity in the loft and that it wasn't a leak from somewhere. You may have difficulty persuading them, as obviously its in your interest to minimise the issue, whereas it is in theirs to make sure the source of it is found and resolved as accounted for before purchase.

Thanks for your response.

There was a very small drip from a radiator which has been fixed and I also had the small bedroom plastered but the window was open whilst this dried.

This has never happened before whilst I lived there and the only thing that is different is that it is now empty.

Next door is empty and has always been empty whilst I have owned that house. There are a few bricks missing between my wall and next doors wall in the loft, if they had a leak in their house could that air be coming into my loft as causing issues? Is it worth boarding this up?

I don't think you'd get condensation to the point of wet rafters and water on the floor. I think you just have a leak and never noticed because who spends every day checking the attic?

Stick a dehumidifier up there to draw the moisture out. I got a Pro Breeze 12l from Amazon and it’s been ace with the condensation in my house.

@Str3bor
Sounds like you need to ventilate the loft more... Read this article, it might help: https://swinglerroofing.co.uk/importance-ventilation-roof-attic/