Additional construction costs when building a house with a developer

Quick question: What does the construction service specification say about the earthworks? That will be the most expensive forgotten item.

I quote from the construction service specification:
"Earthworks:
The native soil is stripped in a thickness of 20-30cm and stored on the construction site on the side. The size of the spoil area is usually determined by the site management to be about 5m beyond the future house edges.
In the case of construction with a basement, the earthworks are carried out as follows:
Excavation of the foundation pit Homogeneous Area I.A according to DIN18300 down to the lower edge of the floor slab, including lateral storage on the construction site. The slope angles and the working space comply with the regulations of the Construction Professional Association.
The backfilling of the foundation pit is carried out after completion of the basement structure with the excavated material stored on the side up to the level of the existing terrain.
A prerequisite is the suitability of the material for backfilling and compaction.
The removal of excess excavated material and its disposal as well as the delivery of additional fill material is included in the price.
A prerequisite for the construction of the basement is a groundwater level at least 0.5m below the bottom of the excavation.
If water retention measures are necessary due to local conditions, these must be agreed upon additionally after examining the local situation.
An assessment of the soil usually takes place by obtaining a soil report. This service is not included in the offer price. If sufficient information about the ground is available (e.g. information from neighboring buildings), the soil report can be waived. The preparation of a soil report is not mandatory according to building regulations. The bottom of the excavation pit is visually assessed by our site managers.

Any necessary soil replacement measures below the aforementioned depth are not included in the offer. Excavation of the strip foundations of the garage or outbuildings including lateral storage and backfilling below the floor slab with material stored on-site is included in the offer.
The design of the outdoor facilities is the responsibility of the builder and is not included in the offer price. (See also point Outdoor Facilities)"

I quote from the construction service description:
"Earthworks:
The natural soil is stripped to a thickness of 20-30 cm and stored laterally on the construction site. The size of the spoil area is generally set by the site management approximately 5 m beyond the future house edges.
For execution with a basement, the earthworks are carried out as follows:
Excavation of the foundation pit Homogeneous area I.A according to DIN18300 down to the bottom edge of the base plate, including lateral storage on the construction site. The slope angles and the working space comply with the regulations of the Construction Trade Association.
The backfilling of the foundation pit is carried out after completion of the basement structure with the laterally stored excavated material up to the height of the existing terrain.
The prerequisite is the suitability of the material for backfilling and compaction.
The removal of excess excavated material and its disposal as well as the delivery of additional fill material is included in the price.
A prerequisite for the construction of the basement is a groundwater level at least 0.5 m below the foundation pit base.
If water retention measures are necessary due to local conditions, these must be agreed upon additionally after examining the local circumstances.
An assessment of the soil usually takes place through obtaining a soil report. This service is not included in the offer price. If sufficient information on the soil is available (e.g., information from neighboring buildings), a soil report can be omitted. The preparation of a soil report is not legally mandatory. The foundation pit base is visually assessed by our site managers.

Possibly necessary soil replacement measures below the above-mentioned depth are not included in the offer. Excavation of the strip foundations of the garage or ancillary buildings including lateral storage and backfilling below the base plate with builder-provided stored material is included in the offer.
The design of the outdoor facilities is the responsibility of the client and is not included in the offer price. (See also point Outdoor facilities)"

That sounds very good. I wouldn’t have thought that is included in the price.

Sounds really good!
Soil replacement could theoretically still be necessary, but for us, the described positions were sufficient.

475+56 would be 531k, so the harsh question is: what happens with the financing if it becomes +15% (= 611k)?

Yes, unfortunately, I am asking myself that question too, or rather trying to estimate what else might be added.

"I hope the fireplace is purely for coziness, plays no relevant role for the heating (calculation), and could also be reserved for retrofitting."

Yes, it is basically "decoration". At least that was the case for the energy consultant, and it will not be executed by the BU either. He only omits the underfloor heating below it and makes the cleaning doors on the chimney for the chimney sweep in the basement and the attic.

"Best if you show the draft in a new linked thread here (so that the completed questionnaire can be in the opening post), because otherwise our ideas of complexity are mostly guesswork; and also add the construction performance specification. With the previous vague information, one can basically only wish good luck, but offer few hints with substance."

Do you mean the questionnaire?

My sketches and what ultimately came of them see below:

The floor plan wouldn’t be my favorite because of all the corners, but it doesn’t have to be. :) Maybe consider making the equipment room accessible from [Keller 2]. That way you can save yourself the dark mini hallway. Something like that can still be changed quite easily.

But: The built-in desk in the office is totally my thing, great idea :D

I like it a lot :)

There is no window in the dressing room, but there are worse things.

With kfw55, fireplace, and double garage, there are actually bigger cost factors.
Altogether also 7 light wells, many rooms, many doors, and a sliding door to the kitchen, which alone cost us 1500€.