How to address my humidity issues

Aloysius1972

Well I’ll start experimenting with much more ventilation once the ladybirds have decamped from my window frames. Opening them now lets an army in….

Baldytyke88

I had mould in my bathroom untill I made the window permanently open, I could not rely on others to open it, so it's open permanently.

fatbelly

I run 4 dehumidifiers on timers in an old house. They come on for about 4 hours per night using Economy 7. I empty them every 3 days.

WIAWSNB

Aloysius1972 said:

Thanks for all the advice. 

I was always conscious that the high humidity in the property was an issue even when we had not been at home producing moisture. So if the attic rooms are, say, 70% in these circumstances wouldn’t something else be needed.

my worry about venitlation is that the outside air here is often even more humid. I know that the RH drops when it is heated up indoors, but if the rooms have no heating this won’t happen and I will just be increasing the humidity further won’t I?

All I can suggest is to try it
You seemingly have two attic rooms you can compare? Ok, make the worst of these the test room, and leave the other alone as the 'control'.
Test room: door closed, heating off, and ventilate literally as much as you can. Eg, if it's secure being up in the attic, you can probably allow the window(s) to be open a good couple of inches. Monitor them both.
Your house felt damp even when empty, but that was almost certainly because it wasn't ventilated correctly. I cannot fully explain how moisture gets 'in' - other than through walls and founds - but I'm pretty sure how to remove it!
If I was leaving our house empty for some time, I'd slightly amend my previous suggestion and crack open every window to 'vent' setting as before (or open the 'trickles' if they have them), but leave all the internal doors open. Since there would be no room inside generating moisture, there would be no need to isolate any by closing their doors. With all the windows ventilating, especially with some on floors above, there should be a very effective flushing of damp air, and I'm 99% certain the house will remain dry and smell fresh on your return. Oh, in winter, either drain 'water', or leave the CH on 'frost protection'.
I've mentioned on here before, on other 'damp' threads, that we often walk through this nearby farm used as holiday lets. There is a large, fully open to the elements, car port there, with WMs and TDs almost always running. Even in piddling rain, on the dampest of damp days, it is bone dry under there, with not a hint of condie on any surface. Bone dry. Even if the newly returned vehicle is dripping. It's quite well ventilated :-)

Aloysius1972

It seems like there are two main options for how to keep the attic rooms free from mould and condensation:

1. Keep the window open all the time for max ventilation, no heating and keep interior door closed to isolate from the rest of the (heated) house. 

2. Keep the window largely closed to preserve heat in the room, heat continually to 16 or 17 degrees at least, keep interior door open and ventilate with open window for a bit most days.

ChatGPT seems adamant that option 2 is far better and option 1 will create and maintain cold surfaces and damp structure that will encourage mould in corners, etc. But as I have two rooms there is one way to find out I guess.

WIAWSNB

Experiment ahead!

Both should help, but work in different ways - and one costs more. 

Yes, as explained by others, you can heat a room and that does help - to a degree. What heating does is to allow the air to hold more of this moisture in suspension. But, it's still there. If you don't ventilate this warm, moist air away regularly, then it'll cunningly wait until the temperature drops - eg you turn off the heating - and all this excess moisture will condense out on the coldest surfaces it'll find - eg your windows, bottoms of walls, corners.

And, if you keep the internal door open, it'll also allow this warm, moist air to escape and find cold spots elsewhere in your house. 

I know it sounds counter-intuitive, but if you shut the interior door to a room, turn off the heating in that room (as it would be a waste), and open the windows fully, it'll be bludy cold in there - but bone dry.

ChatGPT may be assuming that you actually want to use that room, in which case my idea is pants! For a room you want to use, then only 'trickle' vent, keep doors shut from sources such as nearby bathrooms and kitchens, heat it to the temp you require, and then - once you're done, and especially overnight when the temp drops - heat off, shut door, open window to a decent vent. 

Next time you go in there it'll be chilly but dry. Close window, heating back on.

Albermarle

Chat GTP vs WIAWSNB  

I await the actual experiment results with anticipation 

ian1246

Would strongly suggest a positive ventilation device. I had one fitted this summer as part of an insulation grant and whilst it blows cold air & does make where it is cooler, in the grand scheme of things the drier air in the house will heat up a lot quicker than more moisture air, so bills should be cheaper. On the colder mornings, I've noticed no condensation at all on the windows - obviously haven't yet had proper frosty nights but I'd say there's been a huge difference.

I paid the extra £80 to get a heated positive ventilation device (I.e. in freezing weather it heats the air blowing into the house).

Aloysius1972

I have begun the experiment. Both rooms began at 73% humidity and 17.5 degrees. One room has windows closed and a small/tiny dehumidifier running. The other has window wide open and door shut. The first room is unchanged but the second room now has temperature of 16.4 degrees and 75% humidity.

ChatGPT tells that whilst this has reduced the dew point and there is less moisture in the air, it has also reduced the gap to the dew point (due to the temperature drop) and therefore increased mould risk. 

WIAWSNB

Albermarle said:

Chat GTP vs WIAWSNB  

I await the actual experiment results with anticipation 

Oi, pal - I'm the one who gave ChatGPT all its false info, so I could reeeiiiign. 

Anyone tried the 'voice' version? It is incredible. But, for complex issues, you need to treat the info with some care.

The wonderful Rick Beato nearly gave it a meltdown :-)

https://youtu.be/TiwADS600Jc?si=PY5CY6QttNiuudP_