Condensation on roof windows

Hello everyone,

I have the problem again at this time of year that there is extreme condensation at the lower and side edges of the roof window. Outside temperature about -15°C, inside about 22°C with 43% humidity. I finished the house two years ago. The window reveal is designed so that warm air can rise along the window. The heat comes from the underfloor heating. We ventilate about 4 times a day for about 5 minutes diagonally. Sometimes only 3 minutes in this cold. The humidity then drops to about 33%, almost too low. Still, condensation forms on the panes in the evening and then overnight. Does anyone perhaps have an idea what I can do about it? Besides ventilating, ventilating, ventilating – we do that and I think we do it correctly.

Is there a film to increase the surface temperature of the pane? Are the roof windows perhaps defective? They have been installed with insulating frames for two years now. The problem occurs on all the windows, which would be strange if they were all broken. Roto sent me new seals, but they did not help either.

I would be happy about any response.

Regards
JonnY

I have the same problem.
Built in 2009, underfloor heating.
The rooms are aired 3-5 times daily for 3-10 minutes.
In the morning and evening, the windows are wiped dry with a cloth.

I even have ice forming on the inside of the windows.

The condensation has already caused stains on the wall.

I am considering whether to commission a building inspection report for this.
Do you have any advice and experience?
Is this normal and acceptable?

Regards,
Dan

We currently have the same problem in our rental apartment. Especially at -10 degrees Celsius outside, the windows are just dripping with water. The only solution is to ventilate, ventilate, ventilate. You only have to leave the window on tilt for 2 hours, then the water is gone. Of course, this is an enormous loss of heat. I don't understand why houses have to be made so airtight and then not equipped with a ventilation system – it is practically impossible to ventilate 3-4 times a day. At least for working people. In addition, unnecessary ventilation (compared to a less airtight house) wastes heating energy, which then has to be reinvested to bring the room back to 20 degrees Celsius. I can hardly imagine that there is any energy saving as a result.

Yesterday I heard a lecture at a fair on the topic of [Passivhaus]. Quote: "Back then, critics used to mock that [Passivhaus] residents would drown in condensation water. So far, no one has drowned." I would have loved to add: "Maybe not drowned, but they all certainly got wet feet."

Hopefully we won’t have that problem – we are building with [Kontrollierte-Wohnraumlüftung mit Wärmerückgewinnung].

Hello,

...I am considering whether I should commission a building inspection for this. Do you have any advice and experience? Is this normal and acceptable?

A very typical case of a local thermal bridge => the windowpane! While exterior walls or roof constructions in new buildings are increasingly equipped with better U-values, the roof windows mostly remain at an outdated development level, i.e., the U-value of the roof window sash (pane) is extremely lower than that of the adjacent roof surfaces. The air "chooses" the weakest point of the entire building construction to condense, here the windowpane. A defect for which the planner is responsible. This is not fixable by excessive ventilation, which would, by the way, lead to excessive heating energy consumption. Best regards

Hello €uro,

A defect for which the planner is responsible.

Yep, you were faster than me

Addition:

@danair

Before you commission an expert: check your contract. I am sure you bought the double-wing windows exactly as they were installed

Best regards

Good morning,

Hello,

A very typical case of a local thermal bridge => ... A defect for which the planner is responsible. This cannot be remedied by excessive ventilation...

That’s easy to say. I built two years ago, so the windows were ordered about 2.5 years ago. The regular windows and doors have triple glazing. The roof windows do not, but they were not even available at that time. At the beginning of 2011, Roto only brought these roof windows to market. My insulation is 22 cm with 0.8, there is no window (frame) on the market that achieves these values overall. My roof windows have 1.2 and that was the best available at the time.

I don’t understand why houses have to be made so airtight and then equipped without a ventilation system – it is practically impossible to ventilate 3-4 times a day.

Because I didn’t want a source of dirt in the house. I have maintained ventilation systems and know what lives in the ducts after 2 to 3 years. Anyway, putting that aside, I have indoor humidity of 33%. That is actually too low, yet moisture still settles.

I still believe it is due to the window seals. Round seals are not miter-cut but simply glued together, which means cold air will always come in at the corners.

You just have to leave the window tilted open for 2 hours, then the water is gone

That is very dangerous! This cools down the masonry at the window reveal and then the moist air settles there. That’s where mold can then spread nicely.

The best thing, of course, is to have a heater under the window, just as our parents did when building their house. But that is difficult with a supply temperature of 32°C at -20°C outside; only underfloor heating works there.

Well, maybe someone still has an idea...