The question is, how exactly did the process take place. Did the craftsman create a written offer? Or was it a cost estimate? Did you make changes to it and commission it in writing with these changes? Or did the craftsman later create a supplementary offer? Do you have a lump sum offer or are there unit prices for different items (stones?) included? Did you agree in writing that the VOB also applies?
The thing about the 20% price increase mentioned here is not true at all. It is not the case that the craftsman can charge up to 20% more money without a contract. On the contrary: if his costs rise by up to 20%, he often STILL CANNOT pass on additional costs to the client, unless it was explicitly commissioned! (BHG ruling from 2008)
If you have agreed to the VOB, then the craftsman must notify you immediately if there are additional costs compared to the contract. He must calculate the costs of a changed service based on the same calculation basis as the main contract. If the stones are then cheaper, the total sum cannot be higher by implication. You can demand disclosure of the calculation basis, i.e. also the delivery notes for the material.
Now I slowly understand why my house was comparatively so cheap...
Knallkörper, you really seem to know your stuff...
So we have 3 written offers, which say “without obligation” and “according to VOB.” So, no cost estimate. The prices are broken down so that it states: unit price xyz, he needs approximately so many of those, which results in a total of y.
Practically, the first offer was a visible roof truss with boards inside the house and the most expensive smooth tiles and a garage with, let's say, an interior not very nice to look at. That was the cheapest offer.
We changed this (offer 2) and added 3-layer panels instead of the boards. It was also fine that the price then went a bit higher. Instead of 28K around 32K.
After a few months had passed, the offer was discussed again because a lot of time had passed. We wanted the garage to look nicer. He offered a visible roof truss and there was a discussion between him and the site manager about using dovetail joints instead. We were told this was purely an aesthetic difference.
But after this 3rd offer climbed to 35,700 (due to the garage visible roof truss and dovetails), we said that is way too expensive, we have a maximum budget of 32,000. It was then agreed to leave the garage as it was in the first offer but to plane the beams. There was no new offer for this. The statement was that compared to the second offer only the garage had changed and this was not so expensive, so they assumed they would agree.
Work began. Then we were called in to choose roof tiles, even though he had already started working. We then chose cheaper ones than in all the offers. Unfortunately, our mistake was that although we commissioned these, we did not insist on a new offer (he didn’t want to do the extra work, as you don’t argue forever about that and assume you’ll agree).
But then the whole disaster with the wrong roof structure happened (see my other thread). Yesterday he even seriously told us that he himself would not install a vapor barrier under drywall plates in a visible roof truss. The drywall plates would be the vapor barrier. What is certain here: the roof structure he made for us is extremely unusual and no one can tell us whether we will really have no problems. But that’s another topic.
In addition, it was discussed on site that he could not make the house airtight. As a measure, all exterior beams were sawed again, built in between, and perlite was filled in. These costs are now also included in the final invoice.
If the 20% rule does not apply, the question would of course be: which offer have I legally actually accepted now?
By the way, after the conversation, he sent us a new invoice for 35,500 instead of 37,000; apparently the tiles were cheaper after all, although it still doesn’t add up. But even this invoice is, for the reasons mentioned above, morally questionable from my point of view.