What indoor temp and relative humidity do you have on a day like today?

Relatively new build, ground floor apartment.

Temp: 23.5c, RH 65%.

1980's semi, temp 22.2⁰ and 61% humidity. No active cooling but occasionally running a ran for the Mrs.

High RH isn't so much of a problem in summer, because there are no cold surfaces in the building fabric for the vapour to condense on.

Just to expand on this a bit. The important thing is the dew point temperature.

So, taking the example from the OP:

Indoor temp here is 21 - 22 C and RH is 82-85%

If you plug those numbers into a dew point calculator you get a dew point of 17C.

So condensation will happen indoors if there's a 17C surface to condense on, which…there won't be in summer, until you open the fridge. But condensation in and of itself isn't much of a problem. Everyone has condensation in a bathroom during a shower, but it dries out afterwards so there's no mould risk - mould requires constant dampness.

Real problems are in winter. e.g. if you have indoor 70% RH at 18C, you only need a 12.4C surface for condensation, and that's easy to achieve if there's cold bridging, poor ventilation, and the outdoor temperature is low.

Ventilation will fix that (because warming up outdoor air drops the RH), but because cold bridging and poor insulation are often in the same building, people (owners, occupiers) tend to reduce ventilation to combat poor insulation, and then you get the bad combo of big temperature differences and high internal RH.

I think.

1980's 4 bed bungalow. Humidity levels hover between 70-80% this time of year. Inside temp currently 21°

Have intermittent problems with mould on ceilings and mildew on clothes - particularly in bedrooms.

Started putting dessicant packs in the wardrobes to absorb moisture.

Open small sash windows every day, and at night - i leave them partially open.

Run a dehumidifier every night and it collects approx 4 litres of water over a 12 hour period.

When humidity levels are high, the bedroom and bathroom doors also expand slightly and get stuck.

No leaks that i am aware of. The bedrooms are the only rooms that have the highest levels of humidity. There are also no wall vents in these rooms which doesn't help with natural ventilation.

Currently 51.4% RH in a bedroom, that has laundry baskets with towels that would have been damp this morning in it too.

Single room MHRV fitted, has made an incredible difference to humidity.

Lumen re earlier post with digital line chart recording of Humidity levels.. Could I please ask what kit you are using for this?

Thank you.

That wasn't my chart 🙂