Sudden addendum after already accepted addendum offer

Hello everyone,

the construction of our single-family house is in full swing. Now our construction company has suddenly demanded an additional charge.

A wooden staircase was included in the construction contract. During the planning phase, we switched to a concrete staircase. Without covering and railing, we were shown a credit of €1145 as an additional offer. We confirmed the additional offer and it sounded plausible to us.

Now our construction company wrote to us that the calculation was wrong and additional costs of €1200 will arise instead of a credit of €1145.

The staircase has certainly already been ordered, but not yet installed.

How would you deal with this? For us, such a subsequent demand is not acceptable. However, we also do not want the money to be recovered elsewhere through non-transparent additional charges.

Thank you very much for your help!

I would first try to have a conversation with the construction company.

So with us, all providers said that a concrete staircase would be significantly more expensive than a wooden staircase. There is the concept of error in the Building Code. I would also simply try to have a conversation.

The construction contract included a wooden staircase. During the planning phase, we switched to a concrete staircase. Without the covering and railing, we were issued a credit of €1145 as a change order offer. We confirmed the change order offer, and it seemed plausible to us.
Now our construction company wrote to us that the calculation was wrong and additional costs of €1200 would arise instead of a credit of €1145.

For us, all the providers said that a concrete staircase would be significantly more expensive than a wooden staircase.
There is the concept of error in the construction code.

A businessman should be able to distinguish between minus and plus, after all, opposite sides of the balance sheet are not simply a “digit slip.” I can imagine that the construction company oriented itself on the principle that the concrete staircase (especially with “construction-side” covering and railing) is cheaper than a wooden staircase—but turned around or curved, this relationship can certainly also tip ...

Okay, thank you very much for your feedback.

Is it realistic that a concrete staircase without a railing and without [Gelände] costs 1200 € more than a beech wood staircase with railing? The staircase is not exposed concrete and is straight.

We will seek a conversation with the construction company.

The construction contract included a wooden staircase. During the planning phase, we switched to a concrete staircase.

Is there nothing about this in your scope of services description?

For us, the concrete staircase was standard and the wooden staircase optional. Therefore, we neither have a credit nor a claim, regardless of which staircase is chosen.