Hello,
although the thread is already some time ago, I am answering on behalf of users who may be in a similar situation.
We bought a terraced house in Cologne from Interhomes 5 years ago. Now it has come to light that the company forgot the dimpled membrane in the floor, so that moisture gets into the plinths. All buyers in the row are of the opinion that this is a defect and must be remedied by the company as part of the warranty service. Interhomes, on the other hand, believes that the buyers should have laid this foil themselves when they attached the terraces. Can someone perhaps give us tips on how to proceed? How can one tell from a finished building that this foil is missing? Doesn't a house have to be handed over as "waterproof"?
What others say must be irrelevant to the OP, because probably having the right and getting the right are two different things!
The OP is burdened with proof, since he either moved into the house 5 years ago or accepted it before. This means he must commission an expert with a focus on masonry and sealing to inspect the property and await the results. Before that, however, he should first look at his contract to see what it says about sealing.
He then provides the expert's report to the provider and demands—if it is positive for him—the immediate remedy of the defect. However, he must expect that the provider will not simply accept this and may send out their own expert. If the latter comes to an opposing conclusion—possibly also based on the formerly concluded contract and its contents—a deadlock arises. Resolving this then requires a lawyer specializing in construction law; if this also does not lead to a solution—always assuming the OP is in the right—the only option left is to go to court. As a rule, a court-appointed expert is then commissioned to inspect the property and based on their report, the court issues a judgment or—what happens quite often—proposes a settlement.
A settlement also means that the OP will have to bear his own expert costs; procedural costs and costs of the court-appointed expert are shared, and he will be billed twice by his lawyer. In any case, the effort must always be weighed against the possible outcome, and one must remember that the OP receives a court judgment, not necessarily justice.
Rhenish regards