Hi, I've been improving a few things in my loft recently, but I've noticed relative humidity sits at 90-92% which is obviously pretty bad and needs fixing. I did have a shower extractor leaking up there for a few weeks which I hoped was the cause, but levels are not receding having since fixed that. There's no longer any visible condensation. I've run a decent dehumidifier for a week but it barely makes a dent, then levels rise overnight with low temperatures. The big thing is, there seems to be no ventilation at all, so I am getting some felt vents to fit as mentioned in another thread but I'm more concerned about what the underlying cause might be? The rest of the house is entirely below 60% humidity and there's no obvious leaks, extractors are all good etc. There is a cold water header tank up there, but that has a lid and appears ok. I don't know how humidity works... but could that 90% just be an accumulation of lower low-humidity rising across the rest of the house? If so ventilation should fix that, but if levels that high imply another problem I would rather identify it asap. Or am I worrying over nothing and should just get the ventilation fixed? Thanks a lot!