Stain on plasterboard ceiling to loft

[Scarum]

Just noticed today a small brown stain in upstairs bedroom (office). No other stains in the house.

Went in to loft to investigate and take photos. No pipes or plumbing in the vicinity. The roof lining looks OK. I have circled a shiny part, is this a sign of condensation?

It's a very hot day today and we haven't had rain for weeks (near Cambridge). If we get a thunderstorm I'll head back up to check (laid some cardboard over the loft insulation) for a sign of leak in that area.

Lifting up the loft insulation I noted the pink insulation was tacky, stuck to the plasterboard, does anyone know it that happens if they both get wet together, or for another reason?

I have a bathroom with an extractor fan, I do wonder if this is not as effective and if this is blowing in to the loft space rather out the top of the roof, another possibly contender?

I have signs of mice in the loft (mouse trap up there right now) but this loft insulation is so thick and there are no signs a rodent has burrowed to this area.

Any thoughts?

Many thanks.

 

[John D v2.0]

When your say just noticed - how long since it was definitely not there?
It looks like humid air leaking through the board joint and condensing in the insulation and dripping back down. But that would only happen in cold winter.

We had exactly that above our ensuite - a gap in the shower board, and the top of the insulation was soaked with condensation which had dripped back down and soaked the plasterboard
Fix was to seal between the shower board and ceiling, and pour dilute PVA on top of the ceiling from the loft.

In your case if it is that I'd be tempted to seal from above and repaint from below.
You would also want to reduce the winter humidity in your house, eg stop drying washing inside and open the windows more often etc.

 

[Scarum]

Thanks for input John D. Weirdly, I do spend time looking at the ceiling in other rooms in the house but not in the office as I usually spend time looking at the VDU! I can see hairline cracks through the beautiful Artex in the stained area, so this holds up to your theory perhaps?

Re humidity, this is something I have been more aware of over the past year so if this stain was a result of humidity from inside that is a shear coincidence. The bathroom is next door to the office as well and in the winter I do like a long hot bath after a long run. From last Winter I now have a mechanical dehumidifier at home for laundry and since the bathroom has no window and just an extractor fan I now use the dehumidifier (outside) the bathroom during a hot bath. I plan to look at cleaning out the venting pipe to give less obstruction (cobwebs and dust etc). I was wondering if the extractor fan was venting to the outside as it should and not leaking in to the loft space but not sure how to test that.

House coming up to 26 years in age, I was worried ridge tiles on roof had failed but I see no sign of water ingress in the loft but it hasn't rained here for weeks so I remain on the look out when it does.