Is 80-90% humidity in loft normal for this time of year?

[dragonfly101]

I recently noticed some cardboard boxes I have in the loft felt slightly damp to touch, and I'm sure they've been ok in previous winters in the loft. No sign of any condensation or dripping from the roof. I've put a weather sensor up there and it's been ranging 5 -> 12 degrees and 80->90% humidity these recent days. Below in the centrally-heated house it's normally 20 degrees and 40-60% humidity.

Wondering if some moist air is leaking into the loft from the house, I had a bathroom extractor fitted a couple of months ago (because of bathroom condensation), the ducting does vent through the ceiling into the loft and out from a soffit. I've checked for any signs of leaks in the ducting when someone was having a shower below and couldn't find any - however I did notice the humidity increase from 83->86% after three family members had consecutive showers. Wondering if the moist air coming out of the soffit vent is blowing back in via other nearby soffit vents?

 

[foxhole]

If it’s well ventilated then humidity levels will be similar to outside air.

 

[KenGMac]

dragonfly101, good evening.

Have you considered using a small volume of smoke to try to ensure the venting system is indeed intact? something like a bunch of joss sticks ignited and held close to the fan extract when the fan is running? pop into the loft and smoke will be easier to spot than low pressure steam?

How well is the loft space cross vented?

Ken