Why do I Have this Damp Patch when the Temperature Drops? Damp can be a major issue in the home. Find answers to questions or post your own here.

[Ashers]

I have a damp patch that comes and goes in the corner of my bedroom. The patch does not appear in the summer or when we have warm rain.

However as soon as the temperature drops outside the patch reappears. The patch mainly appears overnight and disappears again during the day as temperatures increase.

What is causing this and how do I remove it?

[thedoctor]

The damp patch is more likely to be condensation than a leak. It appears when the walls are colder because the warm air is hitting a cold surface and condensing. See our project page on condensation here https://www.diydoctor.org.uk/projects/condensation.htm

When the walls warm, the air does not condense. Bingo - no mark.

Ventilation required to stop this happening

[Ashers]

Based on that should the insulation above be in the gap between the wall and wooden rafter.

[Ashers]

Based on the above post, should there be insulation between the wall in the attic (attached to next door) and the wooden beam or is this leading to the poor ventilation.