Garden house – Regulating humidity

Hello,

this summer we set up a garden house for two fitness devices, which we also want to use for about 1 hour per day during the autumn and winter months.

Lasita Maja Domeo 1
Base area 3m x 3m
Wall thickness 44mm
14mm insulated glazing

The assembly was done on a slab foundation made of terrace slabs about 10cm above ground level. To protect against rising moisture, the substructure was sealed from below and on the sides with pond liner. The floor was insulated and equipped with a vapor barrier. All the wood was completely treated with wood protection primer before assembly and, after assembly, treated on the outside with a wood protection glaze. To ensure ventilation, I installed an exhaust fan (80 - 150 m³/h) in conjunction with a temperature and humidity sensor and also attached a 450W infrared heater, all of which is currently controlled as follows via home automation.

Temperature above 35 °C = fan on
Temperature below 5 °C = infrared heater on (frost protection)
Humidity above 70% = fan on
Daily at 03:00 = fan on for 1 hour (daily ventilation)

What I now have to find is that the regular daily ventilation causes the humidity in the garden house to currently rise to 69% and only after a few hours fall back to the original value of about 67%. Apparently, the outside air has a slightly higher humidity than the inside. But ventilation is actually supposed to ensure that the moisture-enriched air inside is replaced.

So now I wonder whether daily ventilation is really sensible if no moisture can rise from below and if the garden house is not being used at that time. Would it perhaps be more reasonable to dispense with automatic ventilation and instead set up a dehumidifier (granulate 400g) and only ventilate the garden house as needed, i.e., essentially during and after use.

I would therefore be interested in your opinion on this.

Regards
Jochen

What in the garden shed actually needs frost protection? The fitness equipment certainly doesn’t? If you still have any paints, etc. in the garden shed, better find a shelf for them somewhere in the house. Otherwise, the heater in that little house runs continuously in winter, using about 10 kWh/day. Better turn it on half an hour before training and off again afterwards. Daily ventilation can be done, doesn’t hurt. But it’s hardly really necessary and combined with constant heating it becomes quite expensive. I would quickly ventilate once after training and that’s it. Such a log cabin is also anything but airtight, so it basically regulates itself quite well.