Uncertainties regarding size, planning itself is so far completed

The average (!) American newly built house is about 254 sqm - the median is 234 sqm. Here in Germany, we simply plan too small. But this insight also took some time and had to mature first. A civil engineer who works in residential construction himself confirmed this to me again. Many costs are fixed anyway, many costs do not increase linearly. To realize about 10% more living space, it takes about 5% more costs for the masonry and usually no additional costs, for example, for house connection costs, surveying, many cost items SHK/ventilation or electrical or interior doors or stairs or front door. He would always build as large as allowed according to the development plan - in terms of the overall project, it doesn't make much difference in costs.

Do you really believe your own talk? You are and will remain a real troll

New construction house sizes for "Single-Family-Homes" are normally recorded by the Census in the USA. They also calculate the median and mean. And what a civil engineer who, firstly, has just built their own house and, secondly, works in the field says, I don’t really doubt that too much. The statements are very plausible and can also be found in house prices from larger providers.

Just as an example, from a well-known provider in Rheinau-Linx you get 129 sqm for 219,000 EUR and 197 sqm for 263,000 EUR. The 68 additional sqm cost 44,000 EUR or 647 EUR per additional sqm. The price includes the foundation slab, which also gets bigger, and includes VAT.

This is serious and calculated at market price. Numerous house costs are fixed costs, and in this case, 647 EUR/sqm are the variable additional costs (including profit, taxes, etc.). Many larger cost blocks arise from the equipment, regardless of whether the house is large or small. A stylish front door and a freestanding bathtub do not cost more or less in a 129 sqm house than in a 197 sqm house.

We had already worked this through for Helma and Viebrockhaus... it was relatively linear with the size. Sometimes large houses were even disproportionately expensive due to certain equipment and design features. Material should logically increase linearly. What you save are setup and one-time costs like scaffolding, construction toilet, utility connections, heating, sanitary installations, etc. Of course, this only applies as long as you don’t suddenly come up with the idea to build a master bathroom because you have a lot of space. Furthermore, it is questionable to what extent additional square meters create added value. 4 sqm more in the hallway out of necessity because there was no other option, 20 sqm bathroom because that’s how it’s done, a dance floor in the living room due to poor planning... even if the additional square meter does not cost €1500 more but only €1200, it could have been saved. In addition, huge houses without facade design quickly appear box-like – facade design then costs significantly more money again – so not much gained either.

A 1-story house 10x10 without interior walls and with a wall thickness of 37cm has 85.68 sqm of living space. The total length of the wall is 39.26 meters. A house 11x10, c.p., has 94.99 sqm of living space and 41.26 meters of wall.

In the first example, you build 39.26 meters of wall per 85.68 sqm of living space = 0.458 meters of wall per sqm of living space.
For 9.31 additional sqm of living space, you need 2 meters of wall, the ratio is 0.215 meters of wall per sqm of living space.

The meter costs what the meter of wall costs. In case B, you have 5.09% more costs for the wall and 10.87% more living space.

That is simple geometry – a natural law.

You cannot compare a small house with a surface-mounted flush tank without a bathtub to a large house with a freestanding bathtub and Japanese toilet and then say that large houses do not cost less per sqm of living space.

The building services block (SHK/ventilation and electrical) nowadays accounts for an enormous amount in every house construction and there are only a few items that increase linearly such as the sqm of underfloor heating. A gas boiler with hot water storage and mandatory solar on the roof as well as the bathroom fixtures, the number of pipes, the central controlled residential ventilation system, the controlled residential ventilation outlets, the number of control cabinets, the number of sockets, etc. do not increase. Likewise, there is no second wastewater connection, no second front door, no additional window if I build a dance hall in the living room, or in other words: space for the children to play. A fireplace does not cost more or less in an 8x8 house than in a 13x10 house. Therefore, I cannot now compare the bare 8x8 house with the fireplace-equipped 13x10 house and say that you do not save much per sqm.

With the same equipment, I have already used an example above. The additional sqm costs 647 EUR.

The material requirement for the wall increases linearly with the meter of wall, and the meter of wall increases by 0.5 X where X is the living space. The material requirement for house connections increases linearly with the number of houses. If the number of houses remains 1, then the house connections do not cost more either.

Don't trumpet things like that around here - people might actually start building everything big. How stupid some are to build small... But stupidity in humans is like overconfidence - a law of nature .