ᐅ Humidity in the Attic

Good evening everyone,

Today I spent a lot of time working in the attic, and the humidity there rose to 96% relative at 5°C (41°F). The attic is not insulated, meaning the insulation is between the upper floor and the attic. No moisture is coming in, everything is well sealed, including the staircase. The roof is also watertight.

The problem during these cold days is that warm air from the living area upstairs condenses, causing the relative humidity to increase when I keep the hatch open for a longer time.

I have a wireless thermo-hygrometer there. Currently, it shows 4.0°C (39°F) and 92% humidity.

At what level does this become critical? Are dehumidifiers effective in such cold conditions?

Best regards,
Tobias

Hello Tobias,

Do you have ridge vents in the roof?

Regards,

Dirk

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

projekthausbau schrieb:
There is probably a vapor barrier under your insulation, right?

The problem was that he had the hatch open.

Exactly. As I mentioned before, I always have the problem when the hatch is open for an extended period.
A vapor barrier is of course installed. The house itself is well sealed, as shown by the blower door test.
As far as I know, no ventilated brick has been installed.

hg6806 schrieb:
At what point does this become critical here? Do dehumidifiers help, especially with cold air?

In my opinion, it becomes critical when there are surfaces where moisture can condense (that is, gaseous water [=vapor] turns into liquid; your wording above is somewhat unclear). If the relative humidity is close to 100%, even a slightly lower temperature is enough. For example, with an attic temperature of 4°C (39°F) and a relative humidity of 95%, water would already condense on a surface at 3.3°C (38°F).

Dehumidifiers can help, but condensation dehumidifiers usually do not work effectively under these conditions. You would need an adsorption dehumidifier.

Is there really no way to ventilate? An attic hatch for the chimney sweep? A hatch for the satellite dish? In my opinion, especially in cold weather, this would quickly help without having to install expensive equipment.

Otherwise: keep the hatch to the house closed if you are working up there for a longer time.