Damp Plaster With Damp Line Around Upstairs Windows

[itsme123]

Hi there, newbie posting!

My house has a damp plaster issue I have been unable to solve, and am wondering if anyone can advise?

The rooms are well ventilated with bedroom windows opened each morning. There is an extractor fan and opening window in the bathroom. I have even tried a dehumidifier to no great effect. I have had a builder check the external window seals which he informs me are in good condition.

Yet, as per the photo, there is a definitive line of damp all around the upstairs windows. Can anyone advise if this is moisture from inside or outside, and best possible remedy?

Thanks in advance.

[VinnyB]

Hey Itsme123

Had this issue on a property I recently inspected.

Can either be one or both of the following:

1. Cold bridging occurring due to poor insulation in the cavity wall.
2. Vertical damp proof course in the wrong place (either because of poor construction or window has been installed too far forward).

Can you answer the following to help me diagnose it:
- Whats the age of the property?
- Is it a solid or cavity wall?
- Have you recently replaced the windows?

From the pic I think it going to be the second of the points below and that you will have to investigate further by cutting/chizzling a section of the plaster out.

I will await your response for the above.

Regards
Vinny