Is it sensible to build a new semi-detached house without the KfW standard?

Hands off. Algae growth will come! For sure.

A sufficient roof overhang and thoroughly executed water drainage at the window sills prevent the worst. You do have a rendered facade and no klinker – I boldly claim that the exterior wall behind the render is just as cold as an ETICS with identical thermal conductivity. Why should more greenery grow there than with you?

I don't know why....but several houses here have beginning algae growth in the northeast after only 3-4 years. None of our monolithic ones are among them.

You may all have biocides in the paint – they just wash out slowly and then end up in the soil and eventually in the groundwater. And before that, they prevent algae growth on the facades. Is the algae growth on the other houses below or above the windows, or on the first meter of height? Or rather evenly distributed?

With us, facade paint with silicone resin. I know nothing about Algizid. But it is possible. It starts around the windows. For example, the styrofoam block is visible under the windowsill. Where there is a joint, it is white; where there is a surface, a delicate green begins. If the owners are careful, they can still reach it well with moss remover. But it doesn't have to be. With us, absolutely nothing is visible yet. Cleaned April 2017. So almost 3 years ago.

I currently still live in a house with an [WDVS] system. This was installed over 30 years ago. The facade could certainly use a fresh coat of paint, but that’s about it.

As if every [WDVS] would turn completely green...