Lifespan of prefabricated houses experiences

I just wonder why the lifespan of solid houses is given as 120-150 years, but for prefabricated houses it's a maximum of 90. [...] Hence my question, what does the lifespan actually indicate.

Most people do not always have all the money for their house themselves – at some point during construction, renovation, or modernization, bank financing comes into play. In this sense, the "lifespan" is an actuarial figure. Just like a "mortality table" for people (how old each generation can be expected to become), there are also statistical values from experience for houses that indicate how long a house will remain a good credit security. The expected lifespan value for solid houses has been empirically confirmed and is approximately accurate. The value for prefabricated houses comes from the growing realization that wooden houses are not so "inferior" to stone houses. How "old" a prefabricated house becomes is still not nearly as precisely calculated as with stone houses. But even some bankers have come to understand that the common opinion (the cardboard shacks can certainly be thrown away soon) is not correct. However, admitting the truth (which is that the oldest wooden houses have, depending on the region, on average about 400 years more on their shoulders than the oldest stone houses) would mean too much "loss of face." The fact is: prefabricated houses "die" prematurely more often due to demolition for fashionable reasons of disregard; some production years of cheap manufacturers also due to biotechnical fears. The earliest "risk of death," however, affects not the construction type "wood" or "stone" but "cheap" – namely buildings of all materials whose common feature is a construction year in the early postwar period.

The fact is: "prefabricated" houses more frequently "die" prematurely due to demolition for fashionable reasons of disdain; some model years of cheaper manufacturers also due to ecological health fears. The earliest "risk of death" however affects not any construction method "wood" or "stone," but "cheap" – namely buildings of all materials, whose commonality is a construction year in the early post-war period.

P.S.: I also assume that certain types of houses from today will soon experience a significant devaluation of trust in their quality: namely "row by row" entire model years of earlier generations of ETICS new builds and renovation projects, and I also see the first generation of basement-less neo-substitute villas "dying young."

that a renovation is no longer economical?

I think it is. The sad thing: in the 70s there were many building sins in prefabricated houses. Toxic substances back then guaranteed the retention of value. Nowadays no longer tolerable. However:

The standard land value in the municipality where I am searching was around €210 in 2021, with 500 sqm of land we are at €105k, which means that the seller still wants €400-500k for a house whose maximum life expectancy has been reached/exceeded. For that I can get a new prefabricated house?!

You cannot use the standard land value: the garden layout as a sign of the times is usually priceless and location is location… a prefabricated house plot in an established location is to be valued very differently than a new development plot.

(which is that the oldest wooden houses, depending on the region, are on average about 400 years older than the oldest stone houses)

although neither the wooden houses back then are comparable to today's prefabricated houses, nor the stone houses of that time to current solid construction methods - purely neutral with regard to which is more "durable." I am still convinced that today's (wood) prefabricated houses are less resilient to damage events, especially involving water, than solid buildings. A leaky roof with water coming from above or a minor flood damage is much more likely to be the death sentence for the entire structure.

You cannot use the standard land value: the garden as a sign of the times is mostly priceless and location is location… a prefab house plot in an established location is to be valued quite differently than a new development plot.

What else should be included in the standard land value if not the location?? That is why it is precisely determined at the residential quarter level and differs accordingly. And of course, this way of looking at it is sensible and interesting – the house hardly has any residual value anymore – so what should the plot cost? This quickly reveals the fantasy price that has been growing in recent years. A wreck to be demolished or a quasi-new build is sold for almost the same price as a 10-year-old house. Of course, often advertised with the double KfW trick. By the way, the garden of the current time is fixed sod around the house, everything else is for enthusiasts.. ;)

Now I find real estate offers for prefabricated houses from the 1970s, which are around 500-600k €. The standard land value in the municipality where I am searching was about 210€ in 2021, with a 500 sqm plot that makes 105k €, meaning the seller still wants 400-500k € for a house whose maximum life expectancy has been reached/exceeded. For that, I could get a new prefabricated house, right?!

This raises the question for me: What exactly does life expectancy mean? Am I in danger that a 1970s prefab house will collapse in a few years? Or does it mean that renovation is no longer economical?

I know these cases - just double the price for the land for fun, then it’s a maximum of 200,000€. Then he still wants 300,000€ - 400,000€ for the building. If it were a 150m² house, that’s at least 2000€/m² - you could have gotten a new build for that 2-3 years ago.
But you have to do a full renovation and are almost certainly looking at another 200,000€. Including all kinds of surprises with pollutant contamination. Then it can also turn out - house value = (-1)*(demolition + disposal costs).

I would wait calmly on that. The typical buyers of such properties so far have been those who only want to do some renovation and move in immediately - no money for a full renovation. Take the 500,000€, and assume 50,000€ equity; currently that results in installments > 2000€. Without renovation.