Cost estimate single-family house with granny flat in Hessen

I have now read several times the figure of 2,500 - 3,000 €/m2 for the calculation of flat-rate construction costs here in the forum. But nowhere does it say what these include. Are these the pure construction costs? Are incidental construction costs already included? Exterior facilities? Land? Could someone clarify for me how this flat-rate number should be understood?

That is probably not really "standardized," which is why it is rather vague and generally only a rough reference value. It concerns the construction costs - meaning the land and its incidental purchase costs are clearly excluded. Accordingly, the individual exterior facilities and groundwork are also not included. Incidental construction costs in the sense of connection costs, which occur for every building, are not included either, as I see it. It is rather what the seller of a general contractor first calculates for you for the house, plus the sum for the upgrade samples that are added later. One could of course debate whether painting & flooring are included or not. For me, it is the price for the complete house without the kitchen on the sandy area of the plot, without anything around it. It remains a good first estimate, but nothing more. And you can use it as a guideline to see whether a price given to you is complete or whether new sums will appear in the further process that someone might prefer to present to the customer in a piecemeal manner for sales tactical reasons. In other words - if you are at 2,000 €/m² there, it is worth looking into the construction performance description to determine what you get for that, in what quality, and what is not included. The quick calculation then takes the form: land plus incidental purchase costs + (living area house * e.g. 3,000 €)*1.25. Incidental construction costs are assumed here as a flat rate of 25% of the house costs, also one of these rough estimates.

I have now often read the figure 2,500 - 3,000 €/m2 for the calculation of flat-rate construction costs here in the forum. But nowhere does it say what these include. Are these just the pure construction costs? Are incidental building costs already included?

Rather 3000-3500€… (2500€ with a very cheap builder with a lot of own work)

It remains a good first estimate, but nothing more.

That's right. And this then only refers to a standard house, plastered, not kfw40 or 10sqm photovoltaic. All extras, not to mention high-end products, but nicer stairs, panoramic windows, etc., raise the average sqm price, regional differences or north-south gradients also play a role.

the larger your house, the lower the cost per m². Items like "setting up the construction site" only occur once and are independent of the size. we ended up all-in (including ancillary building costs) at just under €3,200/m² for KfW55 standard without photovoltaic, fireplace, or "smart home" in the Rhine-Main area. Moved in in August last year. The exterior facilities, except for the driveway and terrace, are not yet finished because the architect's cost estimate, despite clear communication, was completely off and we simply lack the money for further work. The €3-3.5 mentioned by without own contribution and frills fits – at least in our case. As so often (and already said here several times), much depends on your demands. We certainly could have built €50,000 cheaper or more expensive and 99% of our visitors would not have noticed and it would not have made the house better or worse.

since the cost estimate of the architect, despite clear communication, was completely off

Would you like to explain that in more detail?

Would you like to explain that in more detail?

In order to obtain (somewhat) reliable cost estimates and offers, we expressed our ideas. For the outdoor facilities, this included, for example, the construction of a terrace and driveway with staking out, enclosure using double rod mesh fence, gate, and lawn. We proceeded as clearly as possible, e.g., by specifying the fence height/length and the terrace surface, or excluding materials (no grass pavers or those dog bone shaped paving stones). The architect was, of course, familiar with the location and the corresponding challenges.
Basically, everything (that is, measurements, quantity, size, and material) was available except for the specific brand/manufacturer to proceed with the tender.

In principle, everything (i.e. dimensions, quantity, size, and material) was available except for the specific brand/manufacturer to go into the tender.

At Radio Eriwan, after "in principle yes," the more interesting second part of the answer always follows [hheh] – so where was the hitch?