Fly infestation in the attic - Experiences

Hello,

we have now been living in our house for 3 months. We have noticed that there are hundreds of flies (houseflies) living in our attic, there are really many. To be honest, I am a bit puzzled because I cannot explain their origin. The attic is accessible via a folding attic ladder, which is always closed. Shouldn't the masonry and roof be so tight that no insects can get into the attic? I fear that next year it won't be the flies, but a wasp population that will spread in my attic (there are very many of them here).

Roof covered with concrete tiles, roof truss made of wood. The attic floor is covered with OSB boards, below them follow insulation and a vapor barrier as well as the ceiling of the upper floor. Masonry made of Ytong stones, not plastered in the attic.

Are there any experiences, tips?

Unfortunately, I can't tell you much about the structure/sealing of the roof. I'm not an expert in that regard. I do have an idea (cold air roof - sealing), but I don't want to possibly write the biggest nonsense here.

A completely different question arises for me:
For what reason do you have such a huge number of flies in your attic?
We used to have huge numbers of flies in the cellar of a rented building. They came in because the landlord required that the plastic garbage bags be stored in the cellar until pickup. Warmth from the heating pipes and plastic packaging, which was rinsed briefly but not completely cleaned, then led to hundreds of flies in the cellar.

So what could be the reason in your case?
Dead animals? (a marten has nested with you and the remains of its "food" are stored in the attic) (dead pigeons) (mice)
Excrement?
Any materials stored in the attic that were previously wet and are now rotting/molding?

Or do you live so far in the countryside near stables that you simply have to live with such a number of flies?

We have now noticed that there are hundreds of flies (house flies) living in our attic, there are really many. To be honest, I am a bit puzzled because I cannot explain their origin.

If there are no food scraps anywhere, and you cannot get rid of the flies with conventional means, only the pest control will help, otherwise they will continue laying eggs happily.

Rhenish greetings

Hello,

First of all, thank you very much for the hints. There are no food items or anything similar stored in the attic. I can’t imagine there being a marten, but I will go and have a look.

In general, we live very rurally here and are the first house next to the fields, so the number of flies is generally high, but in the attic it is enormous. What worries me more is the next summer - especially because of the wasps!

My specific question is actually the following: Is this normal for a cold roof? Can someone else with a cold roof report whether insects can be found up there??

Hi,
we had the same thing about 4 weeks ago, and if you tapped on the underlay membrane, you could really hear rustling behind it. I don’t even want to know what was back there.
The site manager explained it to me like this: the critters look for a warm spot at night when the cold weather starts. And that is under your roof tiles after sunny days, because they are warm in the evening. If the underlay membrane is open somewhere (it was with us, since work was still being done on the chimney), you have the pests in the attic.
For us, it was also the case that the insulation was not yet installed, meaning the roof wasn’t completely closed at the point where it rests on the upper floor ceiling.
That should all calm down significantly; they won’t survive the winter.
At first I was a bit skeptical about this explanation, but so far it really has been quiet up there.

Best regards,

Andreas

Thank you for the previous answers! Yesterday, a conversation with my [GU] brought some clarity. It seems that the bonding of the underlay membranes did not take place - I can see directly through them onto the roof tiles. He will take a look and make corrections. I will get back to you once our site manager's inspection has taken place.