Construction costs are currently skyrocketing

Incorrect air exchange rates planned in the bedroom (e.g., just 1x supply air and that’s it). Overall, the design only accounted for two people, but there are actually four people in the house. Poor positioning of the ventilation openings. Etc.

Thank you for your answer. But isn’t it normal to have only supply air? And exhaust air in the bathroom and kitchen? How is the ventilation designed for multiple people?

Thank you very much for your answer. But isn’t it normal to have only supply air? And exhaust air in the bathroom and kitchen? How is the ventilation designed for multiple people?

Yes, but if you have a high air exchange rate and only one or too small outlet, that firstly causes noise and secondly increases the system pressure, which works against the fans and thus reduces the total air volume again. Unfortunately, controlled residential ventilation is almost always designed for a 0.4-fold air exchange. That is usually too little because, for example, a 16m² room with a ceiling height of 2.5m has a volume of 40m³. At a 0.4-fold air exchange, that would be 16m³/h. That is much too little even for one person; here you should aim for at least 30m³/h per person. I designed my system for a 1-fold air exchange for the house (I used the rest for ventilating the warm roof). However, I also have 125mm ventilation pipes and not the 70mm "children’s pipes" :p. Because if those are too small, the air velocity increases so much that you get an annoying whooshing noise.

Unfortunately, controlled residential ventilation is almost always designed for a 0.4 air change rate. This is usually too little because, for example, a 16m² room with a ceiling height of 2.5m has a volume of 40m³. With a 0.4 air change rate, that would be 16m³/h.

To stay on topic: With pointless oversizing, it becomes way too expensive. Off topic: Your figures are wrong, a global design at 0.4 air changes means that, thanks to air leakage between rooms, the effective air change rate in many rooms is already around 1 in practice. Just take the Zehnder standard design, use two supply air ducts in the bedroom and wherever quietness is needed, and that’s good. And in the bedroom, possibly actually specify a higher air change rate, e.g., 30 or 40m3/h. It was noisy for me at first, due to incorrect commissioning. I carried out commissioning again myself and directed more air where I need it, and then it was quiet and the air change rate is now at 0.3, more than sufficient.

No, they are correct, and I never wrote that I always and only use the 1-time air exchange. Normally, I am also at 0.3-0.4 air exchange. But when the place is full, you can simply move a bit more air. I am not the "save wherever possible no matter the cost" type, but rather the "better to have than to need" type. Costs are also within the range from 300m³ to 500m³.

The most important question regarding the further evaluation of real estate prices is likely the development of incomes. If we look at the last 50 years in Germany, prices in West Germany have steadily increased.

If we base it on the DM, today we are talking about prices for a single-family house between 1 - 1.5 million DM. Twenty years ago, when the Euro was introduced, prices ranged between 200 - 400 thousand DM.

The payout of my life insurance policy in 2034 should amount to 600,000 DM, a very high amount in 1996, the year of conclusion. At that time, the insurance agent told me, with that amount you can buy a house and still live well for another 20 years.

Many people back then also financed their real estate with capital-building life insurance policies. It all went wrong. I have long since canceled my life insurance. Probably the sum in 12 years would just barely be enough for a new car.

In 1990, shortly after reunification, prices in East Germany quickly aligned with West German levels, but only for about 2 years. From 1992 prices fell again, then dropped completely until around 2005. At that time, real estate was practically given away and worthless. Keyword junk properties, etc.

From 2010 onwards, prices rose again and real estate prices have increased significantly ever since. Adequate to the interest rate cuts.

However, if we fall into a depressive economic crisis with mass unemployment and a currency crisis, which would force the state to drastic restrictions and austerity measures, prices could also drop massively in West Germany.

If one opts for inflation from the central banks, we will laugh at today’s prices and talk in 10 years about prices ten times as high.

Since no one has a crystal ball and the pendulum can swing in either direction, currently every position carries extraordinary risks. I will keep my feet still for now.

The payout of my life insurance in 2034 was supposed to be 600,000 DM. A very high amount in 1996, the year of conclusion.
The insurance agent told me that with that amount you could buy a house and still live well for 20 years.

The statement was nonsense even back then, without involving hyperinflation. Over a period of 38 years, money loses more than half of its value at 2% inflation. If we then assume 200,000 DM (or the equivalent of 400k DM in 2034) for a house, there isn't much left to live on for 20 years.
But if you sell retirement provisions and don't advise, then such details are of course just a nuisance ;)