Price increase - Our construction company wants 21.4% more

A little input from someone not building with a general contractor.

Offer January to August 21’ shell construction single-family house 171m2
min 1.8%, max 35% increase and on average 12.6%. Steel, concrete, wood are the major cost drivers

Brandenburg, east of Berlin.

Question:
You received an offer for the shell construction in January with prices for steel, concrete, etc., right?
So why is it getting more expensive now if you accepted the offer?

What is included in the costs per sqm? Do I also count the sqm of the utility cellar? Kitchen, outdoor facilities in EL, complete incidental construction costs such as structural engineering, civil engineering, etc.?

On the subject of price per square meter. A semi-detached house is currently being offered in our region (Westpfalz) by the developer. I have deducted ancillary costs and the land. This results in €2300 per sqm. Excluding outdoor facilities, of course. It is still under construction. We are currently just starting to look for a general contractor.

Does a fireplace actually count as incidental construction costs or is it allocated to the square meters?
A masonry stove for 15-20k makes a quick difference there.

does a chimney actually count as ancillary building costs or is it allocated to the m2?
a masonry stove for 15-20k quickly makes a difference.

These are the questions, what is included and how do you compare it?
The following items are included with us:

- electric shutters
- 10 m3 rainwater cistern
- photovoltaic system (13.29 kwp)
- controlled residential ventilation
- increase to 3.00 m (shell construction height)
- chimney including chimney duct
- windows coated on both sides
- etc.

There are so many things that you could include or exclude. That makes a comparison price really difficult, as it would have to be standardized.

Does a fireplace actually count as ancillary construction costs or is it allocated to the square meters?

Ancillary costs are expenses incurred alongside the construction. A fireplace is built and belongs to the house. So, in answer to your question: Yes, it naturally belongs to the construction costs, just like the luxury bathroom or KNX.