Price increase - Our construction company wants 21.4% more

In which place is the headquarters of the GU K....... Business partner supplies many companies in the industry with films. Perhaps I can find out something there.

Silence does not count.
Did you receive this information by phone or in writing?

Costs arise from sampling regardless of the price increase

The explanation was given as follows. I really understand the company; we did not even withhold the 5% in the first payment that we could have withheld according to law/contract. I transferred the entire amount because I assumed a fair business partner. I have learned too little from the forum.

"You bought a house from us on 12/29/2019 from Mr. xyz.

The development of prices this year is unprecedented.
In recent decades, the annual price increases from our suppliers averaged between 1 and a maximum of 3%. This used to be a reliable basis for calculating fixed price offers. The current increases are 10 times higher!
Margins on the other hand remain in the low single digits. Therefore, we had to take this measure to protect ourselves from extreme losses. So within a few months, we experienced more intensive price increases than in the entire previous decade combined.

The beginning of the material price increases was in the wood sector. Due to the trade disputes between the USA and Canada that began at the start of the year, the quantities of wood that Canada delivers to the USA were greatly reduced. Germany then, as the most important European wood supplier to the USA, accordingly supplied large additional quantities of wood and wood products to the USA as compensation. Houses in the USA are predominantly built from wood, so the demand here is very high. Prices in the USA rose by up to 400%. Although this was an extreme overreaction that would eventually normalize, this was our belief at the time of the contract conclusion, since construction in the USA—as a highly important economic sector—would collapse at these prices. Fortunately, this happened beginning in June, and the price of wood in the USA returned to an acceptable level by late June.
Unfortunately, the hoped-for relief for Germany has not yet materialized, as China has taken over the role of the wood buyer after Russia apparently reduced deliveries to China. We hope for a short-term decline here. In our current prices, we have already factored in a 40% reduction and fervently hope this occurs.

Further consequences include long delivery times and supply shortages for all wood products, meaning not only our construction timber but also roof battens, OSB boards, wood fiber insulation boards, etc.
For more and more products, we currently receive only limited delivery quotas. This means we do not receive as much as we need but only as much as the supplier "kindly" allocates to us.
The drastically increased prices are also non-negotiable. We can only rarely activate new suppliers, as many suppliers serve only existing customers due to the bottleneck situation. Thus, alongside rising costs, we face increasing difficulties in maintaining production at our current high level.

For some products, agreed conditions have meanwhile been canceled. Force Majeure / act of God is cited here. Thus, even valid delivery contracts have not protected us.
In general, plastic-based products are currently difficult to obtain. This apparently stems also from refineries producing less kerosene, and the resulting by-products needed for many plastic products becoming scarce. This also affects paints, silicones, and plasters. Especially problematic are KG pipes, perimeter insulation. Price increases range partially between 50% and 100%.

Copper has also increased by about 40% compared to the previous year despite a recent decline within one year; high prices currently always signal a supply problem, which especially concerns electricians; one of my electricians currently still has one roll of cable.

Less severe are products that became "only" 10 to 20% more expensive, such as staples, nails, screws, steel beams, and plasterboard. However, such products are the pleasing exceptions.

For your construction project, this means specifically:

The fixed price guarantee was limited until 06/30/2021. According to our sales, delivery, and payment terms § 4.1, thus our new price list applies. Prices for your construction project are now 21.4% higher due to the above problematics.

We would be happy to discuss the situation tomorrow before the sampling."

In this conversation tomorrow, they will probably say the same thing to you in words, that does not sound like a willingness to negotiate. In my personal opinion, someone is writing a lot and at length there, which at first glance does not sound like a legally secure solution. Ultimately, you currently have no secure legal knowledge, which is why you run the risk of making commitments or decisions in a understandable state of shock that you better should not make. Of course, one is considered innocent until........., but the suspicion arises that you have been deliberately put in this pressure situation, because these stated reasons did not just appear out of nowhere today. I certainly know too little about your situation but with the current knowledge, I would tend to cancel this appointment, because how should you be able to decide about tile color etc. without price clarity, plus the deep-seated, justified anger in your gut. In my opinion, that is completely unprofessional and to me it feels like being at a bazaar. I have no solution but I believe that I could not or would not want to build with them, I would want my position to be evaluated and respected in the best possible way. That is crappy and difficult, and the manner is downright mean. Ultimately, they have loudly trumpeted in their partly convoluted letter, whether the music will then legally be played the same way I would definitely have clarified beforehand. A consumer advice center can be a first, simple step. As I said, that is my opinion about how I would probably do it even though I certainly cannot put myself in your shoes.

My impression was also "what nonsense". It read like an article in a tabloid paper. My (completely amateur) opinion? If it were legally sound, they would have sent you a letter and briefly and succinctly announced the price increase. Without chatter and blah blah. Whoever is confident doesn’t bother writing such a long story. Edit: especially linking some sources! Very questionable.

One thing I do not understand, however. Was it not contractually agreed upon how the price increase may be structured after the fixed price period?

If that is the case, then they can arbitrarily come up with any number without providing evidence.

There was once 0.6% per month on the table! If they are contractually agreed upon, one should be able to rely on that!