Delayed house completion - withhold money?

... It can't be that orders were placed until August 2016 and delivered a year later, and I still have to pay the same price as agreed, right?

You can't see it that simply.

Your question asked NOW shows that back THEN you didn't handle each other's mistakes properly. My opinion.

Even back then you should have worked with written deadlines.

My humble layman's opinion

Hello, yes unfortunately we should have put that in writing.

We had a struggle to get a new facade out of court at all.

Can I claim the costs of the expert report? After all, it was €600.

Add another 300 to 500 euros and get advice from a specialist lawyer for construction law!

IMHO you should not pay the final installment; also do not respond to payment reminders (at the latest, however, to the court payment order).

The -- according to your descriptions -- significant exceeding of the agreed construction period and your expenses due to the defects certainly justify withholding damages. But that only works if everything is done correctly in a formal way*. And that is only possible with appropriate legal advice.

* Remind at the right time with the right phrases and set deadlines.

I would not enter the fight like that. Everything has been eliminated after all.

Without DELAY no delay DAMAGE.

If no deadline is contractually specified, the delay (e.g. through a reminder) must be proven to have been caused first.

Specific damages must be specifically stated.

The contract could also include a prohibition of set-off with claims that are not recognized or not granted by a court - which can be ineffective against consumers.

If necessary, the lawyers of a consumer advice center would be a first, inexpensive point of contact. One should not act without consultation.

If no date is contractually specified, the delay (e.g. by reminder) must first be demonstrably caused.

From my own experience: Even with a date, a reminder must be issued; only in this way is the contractor put in default. Therefore, our questioner should have sought advice back then. So? Better late than never (to a specialist lawyer) or write off the matter? We cannot make that decision for him.