Damp caused by frost?

[Sam239]

I had a damp patch under a ground floor window around a year ago. I re-sealed around the window in question, it dried out OK and I re-painted the wall a few weeks ago, so seemed to be problem solved. However, got up this morning to find a damp patch had appeared directly under the window. Only thing I can think is that last night was the first hard frost I have had this winter, but not sure why that would cause it? Any ideas? The patch is not in exactly the same place as the original problem, so it isn't the old one that has just started showing through the new paint. Any help appreciated.

 

[JohnD]

photo would help, inside and out (showing ground level and position of DPC and airbricks).

Is it a bay window? is there condensation on the glass?

 

[Sam239]

Thanks for your reply - I will take some pictures when I get home this evening. No, not a bay and a small amount of condensation.

 

[^woody^]

Temperature drop and a thermal bridge = condensation.

 

[Sam239]

Hopefully this shows the problem. So what would cause a thermal bridge? Debris in the cavity?

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[^woody^]

The pattern looks like surface condensation running down.

 

[AronSearle]

Thermal bridge just due to lack of any real insulation, and general crappy UK building methods (solid materials bridging the cavity around windows).

Upgrade the wall insulation, or increase ventillation (or use a dehumidiyfer).

 

[Sam239]

Hmmm, maybe that's it then. We are running a dehumidifier though. Bought it a couple of months back, as we have a couple of other problematic areas (musty smelling low-level cupboards in the kitchen and peeling paint on the inside of a window recess the other side of the room from the one in the photo). Doesn't seem to have improved things a great deal, but there's not a lot of other ventilation - no trickle vents in the windows and I don't think there's a way to retro-fit them. Currently no extractor in the kitchen, so maybe that would help.

 

[AronSearle]

No point increasing ventillation and running a dehumidiyer, your just wasting energy trying to dry moving air.

Increase ventillation, or decrease it and make full use of the dehuidifiyer (if it is capable of the loads needed).

Remember at this time of year it is still mild and humid (on average), so it's an uphill battle trying to reduce internal humidities with background ventillation.

Upgrade the insulation for a proper fix.

 

[Sam239]

Yes, I see what you mean. I have read that cavity insulation can make the problem worse if I do have some penetrating damp, so that worries me a bit, as well as the cost! Oh dear, not an easy answer it seems...