ᐅ New Construction KfW 70 House and Your Feedback on Our Project

May I ask why?

Hello,

In my view, a mechanical ventilation system with heat recovery is more than just a comfort feature in today’s construction methods.

Buildings are now built so tightly and well insulated that there is a constant risk of mold growth if ventilation is insufficient.

According to manufacturers’ guidelines, someone should generally be present in the house to operate ventilation properly.

Besides that, with a mechanical ventilation system featuring heat recovery, I don’t lose the costly heat I’ve generated by opening a window.

We were initially skeptical as well, but now we wouldn’t want to miss our mechanical ventilation system.

Best regards,
Dirk

stiff80 schrieb:
Maybe I should have phrased it better: which measures achieve the best price/performance ratio.

Doesn’t that idea contradict building a bungalow with over 240 sq m (2,583 sq ft) of floor area? Or did I misunderstand something?
With a two-story house (to put it simply), you would have less exterior surface area and very likely better performance values – at least that’s how I understood it as a layperson.
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Actually, houses today are supposed to be insulated well enough that mold should no longer be an issue! Except if there are thermal bridges or if the window reveal is allowed to cool down through tilt windows – and that’s where mold and comfort can conflict. If you avoid that, the result can be extremely musty and unpleasant.

I think you both have some points:

ypg schrieb:
You know your argument is flawed?
Precisely because the insulation is so good, the risk of mold formation is high.

Then houses in the past shouldn’t have had mold. But they did, and not just rarely. In those cases, besides thermal bridges, rising damp is often the problem.
Moisture needs to get out of the house, whether it’s a new build or an older property.

ypg schrieb:

but from the transpiration of our bodies (several liters per night, though I’m guessing how much exactly),

Several liters sounds good—I’d be a few kilos lighter every morning then. Sleep diet!
Off the top of my head, I’d estimate about 500ml (0.5 kg) when comparing scales in the evening and morning.

ypg schrieb:

So with heated air, rooms that aren’t ventilated are prone to mold.

It’s true that mold appears where there is moisture.
The problem isn’t the heated air itself but rather large temperature differences.
If you leave a room unheated but with the doors open, mold will develop in that unheated room.
Warm, moist air from other rooms cools down there, can no longer hold the moisture, and it settles on windows, walls, etc., precisely where mold forms.
We had this problem strongly in our last apartment. The study was also the cat’s space, so the door was always open. Mold problems appeared in the unheated room. But when we turned the heating up slightly, it improved.

In summer, it’s a similar situation but without the heating:
Warm, moist air outside, cool indoors due to thick natural stone walls. Tilting windows caused mold on the walls.

At least in our solidly built house, we managed well without a mechanical ventilation system. Ventilating thoroughly twice a day has so far prevented mold.
Mechanical ventilation saves you some time. Whether those 20 minutes daily for opening and closing windows 2-3 times are worth it is a personal decision. The same goes for other handy gadgets ranging from everyday appliances like dishwashers and washing machines to automatic vacuum cleaners, robotic lawnmowers, and automated irrigation systems.

Yvonne, you are of course right – for growth, it doesn’t have to be “cool,” but at least 10°C (50°F) – however, for water to condense from the air on the wall or window, the surface temperature must be cooler than the air temperature in certain spots.