Extension of construction time due to scaffolding

If not signed, from the perspective of the construction contractor, I would first build the front house. This would legally secure the construction obstruction notification for the rear house due to inaccessibility, allowing for a pause. The "guaranteed" completion date would be postponed without a contractual penalty.

If it actually came to that and was that severe, then the rear neighbor would have to demand the front neighbor to remove the scaffolding, which the front neighbor would have to pay for. That's where the right to use ladders, etc., also comes into play.

10 years of friendship aside, as soon as four-figure extra costs arise (maybe just 1 month delay for the rear house would be enough for that), it will be an enormous strain. Four adults... only one stubborn person is needed.

Therefore, once again the urgent advice is to talk to the construction contractor about what he thinks would work best for everyone and how much delay he estimates. Find a solution and then sign it. Not for the construction contractor, but for the friendship.

Can you upload a drawing of the property situation? 4.50m width for the construction road + scaffolding is really very tight.

3m construction road might be enough for a car or delivery van, but with a truck it won't work anymore, as it needs space to steer.

I see either construction one after another: first at the back, then at the front, or "front" completely forgoes scaffolding on this wall and uses a flexible rolling scaffold.

These requirements (3 meter construction road, crane positions (2x 8x8)) all came from the construction manager. We are also not concerned about a one month construction delay.

Much more, in this letter, it sounds as if we are signing a blank document, and if, for example, the windows take longer, that it would be "ok" with the letter. This is our problem.

Furthermore, the letter was presented to us with the statement "Sign, or we won't start." A meeting on site to discuss this was declined.

This would make the construction obstruction notification for the back house due to inaccessibility legally secure in order to pause

Just let that sink in: The contractor sets up scaffolding in the driveway to the construction site and then writes an obstruction notification to the clients because his own scaffolding is in the way?

"Obstructions" in this sense are circumstances that lie outside the sphere of the company (weather, progress of other trades, poor preparation by the client, etc.), not faulty planning of the company itself.
If this procedure were "legally secure," any contractor could arbitrarily stretch their schedules by, for example, placing a few pallets of bricks "unfavorably," or simply stating that they ordered the windows too late.

What Hix says.

Yes well.... The question is, what do you want to do? You can let it escalate (as in another thread here), or you can try to find another solution. Financially, the (I guess) developer has the longer breath. He lets you bleed out. You have already signed everything, right? So also the financing? What is the payment plan? Also with two parties involved, you are not in the stronger position. The question: Have you already communicated your concerns? Let him know in the sense of: we are afraid that... We want to push this forward quickly just like you...