Humidity and condensation got worse

[Custom45]

Hi
A while back I posted about high humidity levels in my loft. A few weeks ago I was getting readings of 85% RH at around 5⁰, now I'm getting 99% RH at around 10⁰ (it's been raining last few days and outside temperature is warmer this week). Humidity downstairs is currently 68% at 17⁰.

There is condensation on gable wall stones (slate blocks) but none on roof felt or velux windows. I've checked and can't see anywhere where air from the house is getting up there. No obvious roof leaks.

The house has two separate lofts, as it used to be 2 houses. They are mostly independent of each other, but I'm getting same readings in both.

Both have most of the eaves blocked with slate blocks that I cant move. Some eaves are partially clear, I'd say about 30% clear in total. I've tried fitting lap vents to open up felt to increase airflow, but still very damp up there.

Thinking of getting a roofer in to take a look, was thinking ridge vents would help? It's a large old detached house with slate roof. Would they need to erect scaffolding to fit ridge vents? Any idea how much 10 vents would cost, all in?

Thanks for help!

 

[Custom45]

 

[JP_]

If it is mostly dry it should be OK, I think. According to the local weather station, outdoor humidity is 100% today, so external air blowing into your loft will be humid.

 

[Custom45]

If it is mostly dry it should be OK, I think. According to the local weather station, outdoor humidity is 100% today, so external air blowing into your loft will be humid.

The gable wall in the picture had quite a bit of condensation on it, loads of droplets all over. The roof timbers feel cold near here and in some places a little damp to touch.

I put same humidity sensor outside, it was reading 87%, 11⁰. Loft is still 99%, 10⁰ and still got condensation on stone gable wall. There's a good draft up there, it's a fairly windy day and I can see stuff blowing around up there.