ᐅ Cutting open the concrete slab due to incorrectly installed drainage pipes

Hello everyone,

I am new to this forum and have become quite frustrated today regarding our house construction. We are currently building a single-family bungalow with an architect and separate contracts for the trades. The foundation slab and masonry work are being done by the same company.

Today, the first outer row of bricks was laid on the foundation slab. It was then discovered that the three drain pipes from the guest bathroom (sink, toilet, shower) were all installed 70cm (28 inches) too far to the left. The drains from the toilet and sink are now located in the hallway, and the shower drain is directly in front of the bathroom door. The architect says this is not a major issue. For the sink and toilet drains, they plan to cut into the slab and reposition the pipes 70cm (28 inches) to the correct location within the slab. For the shower, there seems to be some other solution. The architect assures me this poses no structural problem. It should be noted that we do not have strip foundations, but a base layer of 25cm (10 inches) foam glass gravel, followed by a 25cm (10 inches) load-bearing slab made of waterproof concrete.

I am paying the architect for construction supervision (phase 8), and yet something like this happens—this shouldn’t be the case. He said that when he inspected the site, there was no formwork board at that location for the slab, so he couldn’t measure it then. Of course, he measured everything else beforehand.

What can and must I do now? Is this really harmless? What rights do I have, and what should I pay attention to in order not to make a procedural mistake? Should I file a defect notice? Document everything? Request a new structural analysis? Do I have to accept it as is? Why build a 25cm (10 inches) slab with reinforcement if it can be cut open and removed without issue in some places?

Best regards,
Heiko

Heik0 schrieb:

I’m paying the architect for phase 8 (construction supervision), and something like this still happens — that can’t be right. He said when he inspected the site, there was no form board in place for the slab there, so he couldn’t take measurements at that spot when he was there. Of course, he measured everything else beforehand.

Sleepyheads alert. You’re going to have a lot of fun with this guy...

Well, it’s definitely frustrating, but I don’t see it as a big problem.
You don’t need a new structural calculation just because of rearranging some pipes.
Why is the architect solely blamed? If the plans were correct, it was probably the framing contractor or whoever installed the pipes that made the mistake.
Of course, the architect should notice, but mistakes can happen.

Can it still be installed later within the floor structure? What is planned for this? Therefore, the panel might not need to be milled that deep.

Alternatively, the bathroom floor could be raised by 7–10cm (3–4 inches) depending on the planned pipe thickness (wood construction), creating a sort of "underground connection level." Downside: there would be a step when entering the bathroom. Also, having a pipe come out in the hallway is inconvenient, especially since it is the 100mm (4 inch) toilet pipe. This might mean reducing the 100mm (4 inch) pipe to an existing 50mm (2 inch) line using a cutting tool. That would be an emergency solution.

@Mottenhausen: You can't be serious about considering something like that in a new build at all? I would see both suggestions only as absolute last resorts, even during a renovation of an old building...

Alternative? A new structural engineering report, a legal dispute to clarify responsibility, multiple expert opinions, and continuing construction in 2025...

I understand TE already doesn’t want to cut through the 25cm (10 inch) concrete slab with reinforcement by adding a 10cm (4 inch) deep trench.