Floor plan: What is living space / usable space?

: You see, there are several correct answers. That's why you need to provide one for the question: What do you need it for?

Thank you for your answers. It is about the fact that we want to create a calculation for the new building and want to know whether we should fully charge the entire area or if there are areas that are cheaper. Because, for example, we will not heat the [Technikraum] and the [Geräteraum] and will not install underfloor heating there.

A m²*price rule of thumb is too rough to make distinctions on a room basis. If you do not have thermal separation between the rooms, it is not sensible to plan different heating concepts. You are still heating the rooms anyway and are simply increasing the thermal loss of the adjacent rooms.

Then the answer can be found here.

When you build a house, the areas are unimportant, unless you have to prepare a house cost calculation for yourself or the bank. In that case, everything inside the thermal envelope is calculated as living space, and outside the thermal envelope a reduced factor is used for cost calculation.

If it concerns your house, then the basement and the garage, provided both are outside the thermal envelope, are usable space and I would calculate them at 1500/sqm.
Everything else will be heated and counts as living space. The balcony is an extra and is calculated separately.

It’s about the fact that we want to create a calculation for the new building and want to know whether we should calculate the entire area fully or if there are areas that can be calculated more cheaply.

A bathroom is, for example, a relatively expensive room – but because of the sanitary fixtures and special requests you can associate with it – less because of the dance floor in between. A storage room is a relatively cheap room – but only a little on the floor area (provided you use cheaper tiles there). What you have there in less smooth/even wall plaster is only very limited and individually convertible to the floor area square meters. And you will also connect a controlled residential ventilation system to it – not as a broom closet, but probably as a "room". And honestly, just for example assuming 2500 euros per square meter: if you calculate all utility rooms at 2400 and all living rooms at 2600, does the difference to 2500 flat across the board really make that much difference?

If your calculation somewhere showed that your money is only enough for 157 sqm even though you want 160*, you won’t solve that by calculating the storage rooms cheaper ;-)

*) P.S.: now it just occurred to me too late that you are the one with the villa on the Ponderosa – how does your question fit with this object at all???