ᐅ Soakaway Pit or Trench Infiltration – Experiences and Tips?

Hello everyone, we are about to build an end-terrace house. We are currently preparing the building permit / planning permission application. Our architect informed us that we need to infiltrate the rainwater on site. The options are either a soakaway pit or a soakaway trench. Our plot is about 200 sqm (2,150 sq ft), with around 140 sqm (1,500 sq ft) allocated for the house. The garden will be approximately 10 m (33 ft) long and about 5.5 m (18 ft) wide. I have just started looking into this topic. We want to keep the costs low and minimize the effort required. What is feasible and recommended for this plot between these two options? And when is the right time to implement this?

The builder has stated the following: "The wastewater pipes inside the house will be installed with the required diameters. All drainage pipes will be routed out of the building by the shortest possible route, either below the basement ceiling or the slab. The drainage pipes located outside the building for wastewater and surface water, as well as the installation of an inspection chamber and connection to the sewer system or a soakaway trench to be constructed by the client, are included in the scope of work up to a length of 7 meters (distance from building to connection), provided that the sewer connection is already on the property and in proper condition."

We understand that a soakaway trench also requires additional approval from the local water authority.

I look forward to your suggestions. Thank you and good luck.

French drain because you won’t see it afterwards and the area remains usable. A swale is just a swale... You will probably need to budget around 3,000 euros.

That's right, a sump pit is useless and looks unattractive. Usually, it’s too small or the property doesn’t allow for it. If it rains heavily, the sump won’t be able to handle the volume and it will overflow into the neighbor’s yard, which could lead to legal action and compensation claims from them for water damage on their terrace.

Infiltration trenches are basically just some “plastic domes” that are buried underground. Just include one or two extra ones, and you will never have any problems again. Keep in mind that the system should be large enough from the start to accommodate future additions like a garden shed or a terrace with drainage. It also doesn’t hurt to lay out the pipes roughly in advance. Pipes cost nothing.

PS: This has nothing to do with wastewater.

PPS: Yes, the drainage system must be approved by the authorities. The sizing of the system is also required. This is standard and usually included with the building permit/planning permission.

Thank you very much for your input.
What about the schedule? When will the infiltration trench be installed? Is it really done at the end when the garden, terrace, etc. are also completed, or already during the construction phase?
Thanks and good luck

Timing is a matter of personal preference.
It also depends on whether the garden will be done soon.

The soakaway trench will probably be quite large in terms of the excavation pit. It might make sense to combine this with the soil excavation for the basement/foundation slab. The excavator used there is large enough. Depending on the garden size, the landscaper will probably use a smaller excavator and might have difficulties with the excavation for the soakaway.
Some landscapers no longer handle tasks like water/sewage/rainwater pipes due to warranty reasons.