Loft Humidity Levels

relicalpha · 13 Jan 2021 at 16:12

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!

relicalpha · 13 Jan 2021 at 16:28

TGha

bremen1874 said:
According to my weather station, the humidity outside is currently 95%.

I'd assume that my well-ventilated loft is going to contain that same humid air.

Do you have condensation/damp issues up there or just humid air?

Thanks, I have recently had condensation problems from the extractor leak which is why I'm now checking to make sure that's all fixed, I don't have a record of what humidity was before that sadly. I guess if it is that high outside and you would expect a cold loft space to match outside levels, then that doesn't suggest a problem? I had just assumed that humidity that high would be really bad for timbers and could trigger mould etc? It's been sitting at those levels consistently for the week I've been checking.

relicalpha · 13 Jan 2021 at 16:35

Ahh I see thanks, so the key is just ensuring it's a well ventilated space so it can get close to matching outside RH levels? As I currently have no obvious ventilation that does explain it, and will no doubt cause a problem so I'll get the vents fixed. I just wanted to make sure it wasn't indicating a hidden leaking pipe or similar

relicalpha · 13 Jan 2021 at 16:45

And if everything is as it should be, there's no issue with high humidity if it's equally as high outside?

relicalpha · 14 Jan 2021 at 23:39

Thanks, still not quite sure I get it though

Ive no issues with condensation anymore, it’s just the consistent 90% humidity in there still that confuses me... I get that’s relative to the low temps, and pretty much the same as outside humidity - but how is that high air moisture content not dangerous for the rafters and mold growth?

even with ventilation, i get your loft will start to match external humidity levels, how does that not by itself cause damp under the current weather patterns? Sure I’m missing a basic understanding of physics here but I’d like to understand it better