Single-family house with a granny flat on a 450 sqm hillside plot

Well, what a coincidence - how things come together again... ;)

We currently live in an old, charming half-timbered house with everything that comes with it (low ceilings, few windows, pass-through rooms, and high energy consumption). Given that, the new building feels like a huge gain, even under the condition that we aren’t actually getting bigger and would really like one more room.
Here, we have foregone a living room in favor of the children’s rooms (at the moment, there are two bedrooms for sleeping children and two playrooms). We actually got rid of the TV years ago, and streaming Netflix on a notebook is sufficient for us right now.
This is currently leading us to consider again foregoing the living room in the new house in favor of another children’s room. This could then be moved to the attic if needed.
What do you think about that?

This could then go into the attic if needed. What do you think about it?

Converting the attic would be another major effort and financial expense. After moving in, you will need a lot of money just to make the house livable. In my opinion, nothing much will happen during the first 5 to 10 years. The garden will also need a swing or a grill with a seating area, curtains, lamps, etc. – the money disappears like butter in the sun. Meanwhile, you have to pay off the house. So where should the money for the conversion come from? Is a significant increase in income expected in the coming years? If not, then assume that the attic will stay as it is. Otherwise, better build bigger right away.

The expansion of the attic would be another major effort and financial expense. After moving in, you will need a lot of money just to make the house habitable. In my opinion, nothing really happens in the first 5 to 10 years. The garden also needs a swing or a grill with a seating area, curtains, lamps, etc. – the money is gone like butter in the sun. On top of that, you have to pay off the house. So where would the money for the expansion come from? Is a significant increase in income expected in the next few years? If not, then assume that the attic will remain as it is. Otherwise, better build bigger right away.

Ok, since huge salary jumps are not foreseeable – we are in the public sector, so we can quite accurately predict what will come in over the next few years – you are probably right and the attic would remain unused. I thought that if the roof and not the floor slab is insulated and the builder roughly installs interior walls, plus a large window on one gable side and later during the expansion an infrared panel heater, then the costs might be manageable. Probably another pipe dream.

I thought that if the roof and not the floor slab is insulated and the homeowner roughly installs partition walls, adds a large window on one gable side, and later installs an infrared panel heating during the finishing, the costs could then be manageable.

Rather not. If you really plan to do that, it’s worth making some preparations. So provide conduit pipes, a sewage shaft, cable connections, and the like - although, that’s actually always worth it. But if you finish it yourself, you pay. Every wooden batten, every insulation mat, partition walls, sockets - nothing is free or cheaper by the dozen.

Indeed, it was probably about selling as many wooden houses as possible. Basically, our plan was to build using timber frame construction. To compare costs, I called a local general contractor who builds with solid construction. Here, they also spoke of about 3000 euros/sqm for turnkey construction.

Be careful with "turnkey." For some, turnkey really means the moving van can pull up; for others, it means the lockable front door is installed. (Ok, slightly exaggerated, but floor and wall coverings are usually missing.) In addition, you have to look closely at what is included in the price per sqm. The flat rates for floor coverings were so high that we could not find any surcharge-required tiles at the tile store; WC, construction debris, etc., everything included, even the insurance. Sockets, lamps, etc., much more than in the usual scope of services descriptions - and still not enough. Don’t disregard solid [construction], especially now without a basement and only according to the Energy Saving Ordinance.

It would be very helpful if the text version of the development plan were also made available, so that we don’t only find out at the end of the thread what is actually not possible or is possible.

I have just converted the development plan, which I only had as a pdf, hoping that it is readable.