Major condensation in loft space

Major condensation in loft space

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motco

12,584 posts

194 months

Tuesday 19th November
quotequote all
Equus said:
tolmie35 said:
...one side of loft bone dry and one wet, dripping from felt....
That's screaming 'microclimate' at me.

There are two mechanisms to be aware of: solar orientation is the obvious one (the side of the roof that gets the sun will be warmer, and less prone to condensation), the other perhaps less so...

I've mentioned on other threads (but not this one, it seems) that part of the problem can be aerodynamic. A pitched roof acts like a very crude aerofoil to the wind flowing over it: a low pressure bubble forms over the lee slope. Low pressure = low temperature, so the airflow cools the roof structure, causing condensation on the inside surface. In this case, increasing roof ventilation actively and very dramatically makes the situation worse, as you're just feeding a nice, continuous flow of damp air across into the roof to have its moisture condensed out.

Obviously, the 'perfect storm' is where you have a roof slope that is both north facing and in the lee of prevailing winds, so I'd be checking both those things as a possible cause.
Part of my house has exactly that scenario (north facing and in the lee etc) plus it is single storey for this purpose meaning kitchen and bathrooms all on one floor with (heavily insulated) roof space above. Cause? Yes, as described, but remedy?

Equus

6,920 posts

49 months

Tuesday 19th November
quotequote all
motco said:
Cause? Yes, as described, but remedy?
There are a number of possible measures; unfortunately too many, and too complex to fully explain here.