Humidity in the attic

Good evening everyone,

today I worked a lot in the attic, and the humidity there has risen to 96% rel. at 5°C. The attic is not insulated, meaning the insulation is between the upper floor and the attic. No moisture comes in, everything is well sealed, including the stairs. The roof is also tight.

The problem now in the cold days is that warm air from the living space above condenses and thus the relative humidity there increases when I have the hatch open for a longer time.

I have a wireless thermo/hygrometer there. Currently it has dropped to 4.0° and 92%.

From which value does it become critical here? Do dehumidifiers help, especially with the cold air?

Best regards Tobias

Hello Tobias,

do you have ventilated roof tiles?

Regards,

Dirk

Under your insulation, there is definitely a vapor barrier, right?

Under your insulation there is surely a vapor barrier, isn’t there?

The problem was that he had the hatch open.

Exactly. As already mentioned, I always have the problem when the hatch is open for a longer time. Vapor barrier is of course installed. The house is airtight in itself. That was shown by the Blower Door test. To my knowledge, no ventilation brick is installed.

At what value does it become critical here? Do dehumidifiers help, especially with cold air?

It becomes critical in my opinion when there are surfaces on which moisture can condense (i.e. the gaseous water [=vapor] turns liquid; your formulation above is somewhat vague). If the relative humidity is close to 100%, even a slightly lower temperature is enough. So, for example, with a 4 °C attic temperature and a relative humidity of 95%, water would already condense from the air on a surface that is 3.3 °C cold. Dehumidifiers can help, but condensation dehumidifiers usually no longer work under these conditions. You would need an adsorption dehumidifier. Is there really no possibility to ventilate? Attic hatch for the chimney sweep? Hatch for the satellite dish? This would, in my opinion, quickly help especially in cold weather without having to set up expensive equipment. Otherwise: keep the hatch to the house closed if you work up there for a longer time.