Extension of construction time due to scaffolding

I wouldn’t sign that. But I would have had the construction contract and LB checked by experts beforehand. Obviously, you didn’t do that. And you probably didn’t appoint your own expert for construction supervision either.....

We have both. (The contract was reviewed beforehand, both families have their own expert for construction supervision)

According to the contract, construction starts after providing our services (construction road, etc.) and the construction company then has x weeks time.
Each family also has a separate construction contract.

We also ask ourselves what would happen if we didn’t know each other, how would that be resolved then?
Both families were contractually guaranteed a separate construction period of x weeks.

After the completion of foundation/ base slab, ground floor walls, ceiling and upper floor walls, roof truss, windows/ front door as well as the delivery of exterior insulation, roof covering and the gravel for the screed at construction site B, the work at construction site A will continue.

What if the windows don't arrive on time, or the roof truss, or whatever, that essentially turns everything into a free pass. And the supposed additional costs are initially for me just a threat, because the contractor might be in the worse contractual position.

The BU is obliged to coordinate its deliveries in such a way that the setup costs for one side of the scaffolding on the access road are hardly worth mentioning. Rather, it may not have the manpower to finish both houses at the same time.

If you don't want to sign this, then there is probably a problem. It may not be your problem now, but the BU probably can't perform magic. Really bad BU. I would choose the reasonable and feasible option, not the impossible one.

but the subcontractor probably can't perform magic

He doesn't have to; he names the solutions himself (dismantling/reassembling the scaffolding repeatedly and/or transporting material by other means).

Of course, that costs extra, but I cannot see on what basis the subcontractor should impose these costs on the client... if not by signing this nice agreement.

The situation would certainly be different if both clients were building with different companies, but a subcontractor who is standing in his own way should not be the client's problem.

I definitely wouldn’t sign it like that.

The construction company dropped the ball during the preliminary planning and now wants the client to pay the price for it.

Just ask if they have ever had such a [Konstrukt] before and if so, where it was. Then you can ask the client how it went.

I wouldn’t be surprised if the company is encountering such a situation for the first time.