I bought (2024) an old house (1980s) that was renovated about 5 years ago (2019). We moved in in July 2024, and about two months later we noticed higher humidity — mostly from water drops on the windows in the morning. I want to share my experience and, hopefully, eventually a solution.
Current humidity in house
We have 3 floors:
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Basement
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Ground floor
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Second floor
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In the basement, we mostly keep the windows open, or use a small ventilation tube in two of the rooms.
One room is also a utility room with the heater for the whole house, so it's pretty warm. I don't care much about the basement for now — I'll look into it more once we're happy with the rooms we actually live in, the ground and second floors.
- The ground floor has a kitchen, living room, and bathroom. My wife cooks daily, irons weekly, and the bathroom gets heavy use.
I started tracking humidity with an analog hygrometer. To my surprise, it was 80% in the morning. Not something I wanted to see, but I expected the house would need some work.
- The second floor seems fine humidity-wise. I bought an IKEA VINDSTYRKA and connected it to Home Assistant
to watch the trend. Surprisingly it's around 50%, so nothing to do here.
Ground Floor
In October, we had to clean the windows almost every morning. Water drops reached 5–10 cm up from the bottom of the glass. Not something we wanted to do daily — especially since my wife has 5 plants on each window, and me cleaning them would mean broken flowers sooner or later.
The simple fix for the window cleaning would be to upgrade the windows. The current ones are 19 years old, and switching to triple-pane would get rid of the condensation (and the flower casualties). But triple-pane is expensive, and it doesn't make sense for windows we'd replace anyway in about 10 years (windows usually last around 30 years). And it still wouldn't solve the main problem: high humidity in the house.
Another option is a dehumidifier. My brother built a house a few years ago and had two from the start, so he lent me one to try. The Rohnson R-9575 seems nice, though my wife complained about the noise on the first day (she later got used to it). It works — it keeps humidity around the set value of 65% (roughly 62–68%, so ±3%).
Later in December, I set the target to 50%. The Rohnson sits in the center of the house, so the corners still run higher — 60–70%. In December, opening the windows easily brings humidity below 50%.
Running the dehumidifier uses about 26 kWh per week, ~110 kWh per month. In Slovakia in January 2025, 1 kWh cost €0.1557, so that's about €16.19 per month.
2025
We dug around the house for exterior foundation waterproofing. A friend excavated down to the foundation, applied two coats of waterproofing, sprayed hard foam, installed a dimpled membrane, and put in drainage. We also insulated the plinth with 6 cm of XPS (couldn't go thicker because the main house insulation is only 8 cm :(). I hoped that would help a bit.
In October 2025, humidity looked like this over a full day:
Basement:
First floor:
Second floor:
2026
We replaced the windows on the first floor, and the water drops on the windows disappeared.
Now we're waiting for autumn to see if mold comes back in the corners. I'm afraid it will — those corners are thermal bridges. We get ~80% humidity in the corner in the morning when all 4 of us sleep in the same room. If the corner hits 14°C in winter, mold forms easily. I started measuring humidity and temperature in the corner and tracking the dew-point spread. If that gap hits 0, I assume mold will start showing up.
I also installed a Shelly 1 in the basement. We have a fan there and a tube to the outside. I set up an automation in Home Assistant to turn the fan on at 62% humidity and off at 57%. It also checks whether absolute humidity outside is lower than inside.
In October 2026, humidity looked like this over a full day:
Basement:
First floor (I no longer use a dehumidifier):
Second floor:
Let's see what the corners do over the coming months. Fingers crossed.