High humidity levels during rainy spells

[Norfolkdave]

It is a very muggy and humid summer but is it normal to have 80 to 82% humidity in an older stone house at this time of the year? Circa 1870s build. It smells more musty during wet days but I’ve not had any mould issues as yet. We only moved in 2 months ago.
Given how warm it is we have plenty of windows left open and even the front door is left open for large parts of the day.
I had a VapourFlow humidity controlled extractor fan fitted a couple weeks ago in the kitchen and it’s just been flat out the past 3 days.
The house does undoubtedly have some issues with damp but in previous weeks we’ve had levels at nearer 65 - 70% RH. It’s seemed particularly bad the last couple days with the sustained rain.
Given the house is airing all the time, could it be that we’re actually bringing in damper air in and we’d actually be better off not leaving everything so open?

We bought a 1900 stone built cottage and found similar high humidity levels internally.

First I would look at Peter Ward on you tube, he has a book called the warm dry home and is a surveyor for period properties. Basically most of the issues you may find are where modern materials have been used on an older property ie concrete and gypsum.

We had our concrete render removed and replaced with lime render to allow the walls to breathe and dry out after 40 years of being sealed with concrete which doesn’t breathe.

With stone walls there is no damp course so the wall works by allowing moisture to evaporate through the line mortar and the stone itself. If you seal this, then walls trap moisture. We did this 12 months ago and humidity is much better. Our standard number is around 50 now. This number was higher previously and lime takes around 1-2 years to allow the wall to dry out completely so it’s slowly moved to this number.

We do still run a dehumidifier but it’s not big and has a 2 litre tank which we might empty every 3-4 days in winter but spring has seen it working more, Maybe 2-3 days and on rainy days 1-2 days.

I’m sure there’s more we can do, we have two ground floor extensions built 40 years ago with very low roof angle around 12 degrees so these don’t run off well and probably trap moisture, concrete floors which force moisture into the walls as they are connected. Our internal floor is lower than the pavement outside ( thank you mr council ) You can cut a gap and lime this gap between wall and floor slab to create a channel moisture can escape through.

Basically you will have to investigate and decide which areas will return the best bang for your buck, as over time your house will likely have many new materials trapping moisture in a building designed to breathe.

Peter Ward will survey your house and tell you where your problems lie, then you can decide which course would be the most effective. If the lime didn’t work we were going to get his survey but so far we are pretty good.

Basically lime everything lol, that allows everything to breathe. Our current situation is, if it rains outside, humidity internally will be mid to high 50’s, nice outside high 30’s and humidifier will be off. It turns itself on and off. Winter is generally lower humidity outside so it’s around 40-50 with humidifier kicking in and out emptying every 3-4 days so not too bad.

It sounds like you are pretty determined so I’m sure you will get ontop of it, but I guess as a rule the older properties do have a propensity to be a bit damp, probably due to the sins committed to them by adding modern materials over time. All the best, Dave