Developer with limited fixed-price commitment - price increases

I need your advice.

I am currently in contact with developers and facing a problem. The developer I favor only offers a limited fixed price guarantee... That means he covers price increases up to 10% until the start of construction (the foundation slab). All price increases beyond that I have to cover.

Example: Construction starts in February 2022 Price increase for concrete blocks 17% in January 2022 Developer covers 10% I should pay 7%. And he wants to do this with all materials.

It is already clear that there will be price increases. Does anyone know the announced price increases and have an idea of how many additional % I should expect? And can anyone estimate the additional total costs roughly for an original construction sum of about 350,000 Euros?

Unfortunately, I don't believe we can start construction this year anymore.

I would be very grateful for any help.

PS: and before someone says "Find another developer": The developer has very good prices compared to the industry and in my opinion treats me very well. I don’t feel cheated by him. He also says that his limited price guarantee is the only "fair" option for both sides.. and I understand that. I just want to estimate the expected additional costs with your help! Thanks :)

How do you want to do that practically? Will an appendix of all building materials and their prices be attached to the contract? You have to calculate the increase from some baseline.

I know about the construction price index. Status at the start of construction vs status at the end of construction. Increased by more than 10%, so payment must be made accordingly for each percentage point over 10%.

Reasonably feasible would only be through the construction price index. With individual prices, you need a bureaucratic apparatus already before the signature to set the comparison prices. The problem with the matter is that you are buying a pig in a poke. You only build once, and one percentage point in house construction is easily 4000-5000€. That quickly adds up.

No, this limited price binding has nothing to do with fairness at all... because as a layperson you have no chance to verify the prices, no wholesaler will give you any information about it. Does the developer give you money back if prices drop? Hardly, right? ;)

Either you trust that the developer won't rip you off and hope that prices don't skyrocket... or you look for a developer with a real fixed price.

No one can currently predict reliably what the situation will be like in January, March, or August 2023. It depends on many factors... imagine if next week not Nordstream but Europipe 1 breaks down... then we won't get through the winter without the building materials industry slowing down... just one of hundreds of conceivable scenarios for this winter.

PS:
Think about why the developer has such good prices... because he can almost arbitrarily raise the prices after signing the contract, of course he can offer you a very low entry price.
That's how almost all public sector tenders work. After signing, the customer is told "Yes, well... you also need this and that and the other, that's not included... but you didn't request that either..."

If the handling and support after signing is still that good... then you can be happy. The fact that it is like this now, when they want to win you as a client, says nothing at all ;)

I think 10% is fair. He also wants to protect himself.