Any help with damp? high summer humidity in unique house

Andy_Hamilton

I may be splitting hairs here but I’m after advice if possible.
Last year we moved into an upside down house which was air tight and had cavity walls filled. Straight away we seen condensation mold on all windows and the room downstairs which is against the hill.
We have put money into the following:
Nuaire PIV system.
Overpowered fan in the bathroom (no more stars in your eyes auditions)
Dehumidifier for the room downstairs against the hill (no true ventilation or adequate heating).
Within a couple of weeks all signs of mold dried up from black spots to greyish dust and cleaned away.
Over the winter upstairs (living rooms) humidity went down from 70+% RH to 40-55%RH.
Fast-forward to the summer…
Heating the house is not an option, during the day upstairs ranges from 20-24 degrees. Downstairs remains stable at 19-20 degrees.
We don’t have any signs of damp or condensation (not even around the bath) but I had a piece of cardboard in one bedroom which felt soft. Measured the humidity with a data logger and its hovering around 70%.
Discounting relative humidity which is temperature dependent I have found the upstairs and the room with the dehumidifier has less moisture than the PIV supplies.
The bedrooms downstairs are cooler parts of the house so moisture would be drawn to these. They have only marginally more moisture than the fresh air from the vent. Adding air bricks to these rooms would probably add to it being cooler rooms.
I know in the winter the humidity levels are well under control as we heat cooler, less damp air.
Should we be concerned about readings higher in the summer?

Sorry for the long post

TheCyclingProgrammer

If it's a humid day then the chances are you'll have increased humidity in the house.

Normal humidity for our house is anywhere from 40-55 which is fine. However in the last month we have had humidity levels in the mid 60s. We have had no adverse effects as it is warm and the humidity drops when the outside humidity drops.

It's good to reduce internal sources of humidity but there's little you can do if the humidity is high outside. Opening the windows just lets more humid air in.

Strider590

I would be looking for sources of humidity and get yourself a mains powered dehumidifier.

TheCyclingProgrammer

Strider590 wrote: »

I would be looking for sources of humidity and get yourself a mains powered dehumidifier.

If the main source of humidity is outside air then no dehumidifier in the world is going to stop it. You may reduce it temporarily but it will just come back until the outdoor humidity drops.

No point in wasting loads of electricity unless it's causing a problem. Humidity in the air in itself is not a major problem unless it's persistent, the problems come from when it condenses on cold surfaces - not a major issue in the middle of summer.

Andy_Hamilton

Thanks for that, I had no intention of adding another dehumidifier for the exact reasons you state (I leave the poorly vented room with one set to smart but it pulls around 2 liters per week).
I have done some research today and found a paper about passive ventilation which states our readings are not going to cause mold as the surfaces are not cold. We are at the point of being comfortable or not comfortable.
The usual high humility being bad for health does not always apply if its caused by fresh air.

getmore4less

As it's a comfort thing the next step is cooling

if sealed, then whole house heat pump recovery/heat/cooling system.

but do we get enough warm humid days to justify the expense

coffeehound

getmore4less wrote: »

As it's a comfort thing the next step is cooling

if sealed, then whole house heat pump recovery/heat/cooling system.

but do we get enough warm humid days to justify the expense

Yes a mechanical heat recovery ventilation (MHRV) system does sound exactly what this house needs. The heat exchanger would have the added benefit of removing some of the incoming humidity too while the interior is cooler than outside. OP, is it a modernist/industrial looking interior? Exposed galvanised trunking and diffusers for such a system might well fit right in.