Consumer construction contract, flat rate, fixed price guarantee

The consumer construction contract with a solid house general contractor is currently being prepared. It concerns the pure turnkey construction of a single-family house.

Topic wording lump sum/fixed price: In the contract, a "lump sum" is specified for the services to be provided by the contractor (AN). Question: Should "lump sum" be better renamed to "fixed price"?

Topic fixed price guarantee: The contract states that "if the period between contract signing and the start of construction is more than 7 months, without this being the responsibility of the contractor,(...) the cost increases incurred by him shall be adjusted." Question: Should/must the cost adjustment be contractually regulated in advance? For example, that after the 7-month price guarantee a moderate cost adjustment is permitted, but at most 0.5% of the contract sum per additional month.

How were/are your contracts designed in this regard?

The amount of the price adjustment should definitely be regulated, for example by the construction price index. I see it critically that the measurement is made between contract conclusion and start of construction. Theoretically, the construction company could simply start later and thus receive more. That wouldn't exactly be legal, but I would avoid the trouble. It would be better, for example, to link it to the building permit.

The amount of the price adjustment should definitely be regulated, e.g. by the construction price index.
What I see as critical at this point is that the measurement is taken between contract conclusion and the start of construction. Theoretically, the construction company could then simply start later and thus get more. That wouldn't really be legal, but I would avoid the hassle. It would be better to link it, for example, to the building permit.

That is a very good hint. I am curious whether the company will agree to that. In our case, the duration of the processing time was the decisive reason for the price increase. (Partly our own fault, as we asked for exceptions from the development plan which were rejected. I wouldn’t do that again for a next construction, I just thought it was a mere formality.)

It would be better to link that, for example, to the building permit

After the building permit, it's my turn first. Earthworks, creation of connections, construction of the access road. The general contractor will not agree to that.

My contract states that the price applies if the building permit arrives within 5 months. But the general contractor takes care of earthworks, sewerage, construction water, and electricity. Accordingly, that is not a risk for him.

What exactly does "start of construction" mean for your general contractor? As soon as the foundation slab is finished? How far along are you really?
Is the plot already developed? That can easily be delayed (it was for me as well, but the general contractor was super fair about the price increase despite exploding costs everywhere).
Depending on the area, the building permit can also take 3 months or more; you should factor that in. 7 months pass quickly.

What exactly is the "start of construction" with your general contractor?

With the creation of the BP

How far along are you really?

Connections are located in the street right next to the property. I will have these laid on the property after signing the contract. For the preparations, we then have to wait until the building permit is granted. Hopefully, the building permit won't take too long, as the construction is according to §34 and strictly follows the neighboring buildings. In addition, there is already an approved preliminary building inquiry for a previously similarly planned house.