Please explain the construction site assessment report

Hello everyone,

as a silent reader, I am now asking my first question.

My girlfriend and I have now reserved a plot of land and first want to have a soil survey carried out.

The plot is to be built on with a house, probably timber frame construction, without a basement.

I have now obtained an offer and various services can be commissioned. However, I am not exactly sure which of these I really need. Can you help me with that?

The following additional services can be commissioned:

- Determination of the water permeability coefficient kf of the subsoil (per test)
- Dimensioning of the infiltration system

- Sampling with subsequent analysis (according to LAGA)
- Sampling including retention for 3 months
- Construction chemical water analysis for concrete-aggressive components according to DIN 4030

Of course, each of these items has its price, hence the question about the services necessary for me.

Thanks for your help.

Greetings from Aachen, Christian

The following additional services can be commissioned:

- Determination of the water permeability coefficient kf of the subsoil (per test)
- Dimensioning of the infiltration system
- Sampling with subsequent analysis (according to LAGA)
- Sampling including retention for 3 months
- Construction chemical water analysis for concrete-aggressive components according to DIN 4030

Greetings from Aachen, Christian

Hello Christian,

in my humble opinion: 1. kf: Allows (more precise) conclusions about frost risk and the derivation of countermeasures during the foundation design (depth, types of gravel, layering) 2. I don’t understand the infiltration system part – I’m not familiar with that (someone else has to comment on this) 3. LAGA: Determines the pollutants in the soil. Excavated material must be taken to a landfill, which costs a lot of money. Often a LAGA report is required. The price depends on the LAGA class; between LAGA 0 and 4, prices can be 4-5 times higher depending on the landfill 4. With retention: Allows you to obtain the LAGA report later, gives you time to clarify things with the landfill calmly or find a cheaper landfill. The report is offered cheaper with the method than if you don’t book this now and need a new report later 5. I don’t necessarily consider this water analysis particularly relevant. Your slab rests on a foundation (deep or shallow foundation with frost protection collar). So the slab rests on a gravel bed. It does not come into direct contact with the existing soil. Therefore, in my view, you can omit this. It is interesting if you build with a basement and want to be absolutely sure.

You also need to clarify what will be done. Deep foundation (commonly 60 cm - 100 cm) or shallow foundation with collar. In the latter case, there is not much excavation. Two neighbors of ours had this – the little amount was spread on the property. I had a deep foundation (80-120 cm).

Best regards Thorsten

There is a basic service package that the soil expert must provide so that, in particular, the structural engineer receives sufficient information for their planning. The expert should offer this quite "normally" at a price of about gross €1,200. If the price is significantly lower, basic services are missing. Investigating soil permeability (infiltration coefficient) is useful if structural waterproofing according to DIN 18195-4/9 or building drainage according to DIN 4095 will likely need to be planned due to moisture exposure of the soil.

Also, for a floor slab or a non-basement foundation on strip footings or on sites on slopes (layered water), the soil’s infiltration capacity can play a role if drainage water from the site is to infiltrate there. It must not be discharged into the sewer system. However, whether this is necessary ("Dimensioning of an infiltration system") can only be decided after the building design.

In my opinion, it makes sense to have the kf value determined. You should obtain up to 3 offers from engineering firms based on a uniform scope of services (specification of services) and then commission the standard scope (short report, about 20 pages) + kf value determination. The remaining services can be requested as contingency items but not yet commissioned.

On the other hand, you must be able to draw the right conclusions from the report before purchase, for example, increased foundation effort in case of unsuitable soil or soil replacement in case of pollutant contamination. For interpretation of the report, you should seek expert advice.

Hello everyone,

thanks already for the provided answers and the brief explanation of the individual points. I have attached the offer from one provider with the additional services. The 1200 € for the basic report confuse me, as the offer estimates 500€. Maybe not everything necessary is actually included or is it a cheaper provider after all?

Thanks in advance.

Best regards, Christian

Indeed - confusing. Without a precise explanation of the scope of services or consultation with the office, I would not commission the report. The geotechnical reports I have requested and commissioned in recent years have all been calculated within the specified price range (region Cologne/Bonn/Aachen).

Attachment: last report from 2015

Addendum: in the Aachen region, the proof of clearance from unexploded ordnance should definitely be provided not only before purchasing the property but also before the soil investigation. The combination of the geotechnical engineer's dynamic probing and unexploded ordnance can otherwise be explosive.

If you buy the property from a commercial supplier, they must guarantee clearance from unexploded ordnance in the contract. The respective property owner is liable for the proof, as well as for clearance costs and possibly also construction delays caused by unexploded ordnance discoveries during excavation. In a construction project in Cologne-Rodenkirchen, architect friends had "forgotten" the proof. When digging the foundation pit, an unexploded ordnance was found, resulting in almost half a year of construction halt until complete proof was provided through aerial image analysis, etc.

GKD - Güteschutzgemeinschaft Kampfmittelräumung Deutschland e.V. - AL quality mark for unexploded ordnance clearance (AL-GZ 901)
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BDG - Berufsverband Deutscher Geowissenschaftler e.V. - Certificate: "Certified Quality Company"
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ITVA - Ingenieurtechnischer Verband für Altlastenmanagement und Flächenrecycling e.V., Working Group for Unexploded Ordnance Clearance