Cost calculation infiltration Drainage application - realistic?

Isn't that a service in the soil survey?

No, those are two completely different things.

Rhenish greetings

1000€ for a bit of calculation and reading tables... phew... I still find that quite a lot

I never claimed that it is _not_ a lot of money

It depends on what task your architect assigned to the engineering firm. I assume they are supposed to simulate different scenarios; then €800.00 to 1,000.00 is quite "normal" and "usual". However, you are not bound by your architect's recommendations due to individual contracting; just request a quote from another firm. Just make sure that the services offered are truly comparable

Best regards from the Rhineland

Hi,

for us, the infiltration calculation cost just under 350.
I already found that a lot for the service provided.

Graf calculates their own systems for free, which was also recommended to us by the infiltration person from the office. There was also another competitor, I think they do that too.

Question: Are there any requirements for infiltration at your place? We simply submitted the application without any calculations or the like. It was specified which water will go into the sewer = roof area + driveway. The rest is allowed to infiltrate on the property. What should one calculate in this constellation. Costs thus = 0.

Roof surface + driveway

... these are basically the sealed surfaces and you then pay for the disposal of rainwater, year after year, over the lifespan of your new house.

To evaluate a price as good or bad, it is important to know which services are included in the report / calculation and which services the building authority / water authority insists on to comply with infiltration on the property and exemption from the stormwater fee.

If you assume a salesperson who has his lists with which he compiles his products, it seems exaggerated. But if the authority requires an assessment according to DWA-A138, evaluation according to DWA-M153, as well as site plans and detailed sections in various scales, the manufacturers’ salespeople generally do not get very far.

I prepare such reports myself freelance and can only say that a report simply takes work. It requires discussions with the builder / authority, the sizing of the system, an evaluation according to M153, the creation of the analysis as well as documents and plans... all taken with an engineer’s hourly rate results in a price range in which your first offer lies.
But it would not be the first time for a home builder to get a 2nd offer.

In other offices, maybe no professor has to be “paid along” to create a simple infiltration calculation.

Best regards

I did the infiltration calculation myself after I had to create a new application due to a change of system. You actually don’t need many data:

- the sealed surface area (house roof, garage, etc...)
- the precipitation amount, or the extrapolated theoretical 20-year storm (can possibly be obtained online or at the town hall)
- infiltration area and infiltration volume (i.e. storage container)

So if you have your precipitation area, you still need the precipitation value for the 20-year storm. With that, you already have the precipitation volume that the infiltration system must absorb. The infiltration area, in turn, indicates how quickly the system disposes of the water. At first, this sounds like a value that is difficult to calculate. However, there is a trick with the infiltration shaft. These have a diameter of DN1500 (i.e. 1.5m diameter), which again gives you an area.

Now you have precipitation volume and the necessary infiltration area. And now you round up really heavily! If you install the stuff yourself, the additional costs are very limited. Instead of spending 1000€ on an old calculation, you can better invest the 1000€ in a larger system. Our building authority immediately approved my method without hesitation. Ultimately, what matters to the authority is just that no water from your sealed surface flows onto the street. The authority already knows how much volume/area is needed for x sqm of covered area at location y and will simply approve larger systems. However, there are some requirements, for example someone from the authority may need to inspect your system (i.e. not just fill it in) and/or it must pass a pressure test...