ᐅ Indoor heat pump in the basement not possible due to groundwater?
Created on: 10 Jan 2023 19:40
B
Baskervile
Hello,
I am currently planning the construction of a detached single-family house. When signing the contract, the general contractor promised an indoor heat pump in the basement, which is also specified in the contract. After receiving the soil survey report, which states a design groundwater level of -1.75m (-5.7 feet), I was told that an indoor heat pump is not possible because the air ducts cannot be sealed according to the relevant standards (DIN).
Is this really impossible or just too risky?
Furthermore, I received an offer for an outdoor installation along with a discount of just under €1000. During the planning discussions, I was told there would be an additional cost of about €5000 for the indoor heat pump. Overall, this feels a bit strange to me.
I would appreciate your experiences and any information on this topic.
A second question about civil engineering work: My general contractor insists on having the excavation supervised by an unexploded ordnance clearance service due to a note in the soil report, without any prior survey. He claims this is now a regulation by the BG-Bau (German Social Accident Insurance for the construction industry). Is this correct?
I am happy to provide further information or pictures if helpful. I hope I have posted this in the appropriate subforum.
Thank you very much for your responses!
I am currently planning the construction of a detached single-family house. When signing the contract, the general contractor promised an indoor heat pump in the basement, which is also specified in the contract. After receiving the soil survey report, which states a design groundwater level of -1.75m (-5.7 feet), I was told that an indoor heat pump is not possible because the air ducts cannot be sealed according to the relevant standards (DIN).
Is this really impossible or just too risky?
Furthermore, I received an offer for an outdoor installation along with a discount of just under €1000. During the planning discussions, I was told there would be an additional cost of about €5000 for the indoor heat pump. Overall, this feels a bit strange to me.
I would appreciate your experiences and any information on this topic.
A second question about civil engineering work: My general contractor insists on having the excavation supervised by an unexploded ordnance clearance service due to a note in the soil report, without any prior survey. He claims this is now a regulation by the BG-Bau (German Social Accident Insurance for the construction industry). Is this correct?
I am happy to provide further information or pictures if helpful. I hope I have posted this in the appropriate subforum.
Thank you very much for your responses!
A
Allthewayup10 Jan 2023 22:08I was no longer able to edit the old post, so here are my questions:
What exactly does the soil report say about the presence of unexploded ordnance? Something must have raised concerns for the general contractor. Building on greenfield land that has never been disturbed before? Are there any aerial photos available from the local authority that could be reviewed? In which federal state is the construction planned?
What exactly does the soil report say about the presence of unexploded ordnance? Something must have raised concerns for the general contractor. Building on greenfield land that has never been disturbed before? Are there any aerial photos available from the local authority that could be reviewed? In which federal state is the construction planned?
B
Baskervile10 Jan 2023 22:20Allthewayup schrieb:
I wasn’t able to edit the original post anymore, so here are my questions:
What exactly does the geotechnical report say about unexploded ordnance? Something must have raised concerns with the general contractor. Building on a greenfield site that hasn’t been disturbed before? Are there any aerial photos available from the local authority that could be reviewed? In which federal state is the building planned? "Before starting any excavation work, a survey for possible unexploded ordnance from World War II must be conducted on the property by a certified ordnance detection service."
Statement from the local authority: "There is no known abstract or specific risk regarding unexploded ordnance for this building plot."
The site is an untouched meadow, previously used for agricultural purposes, and is located in Bavaria.
B
Baskervile10 Jan 2023 22:27Allthewayup schrieb:
Now I understand it a bit better. The heat pump doesn’t have an outdoor unit and is therefore connected through very large duct cross-sections for supply and exhaust air. That explains the external air shafts—now a lot makes sense. This is a completely different issue than I initially assumed. I looked up the unit installed via image search on the internet and can now understand the general contractor’s approach a little more.
Try calling the manufacturer and ask if there is a watertight building penetration available for this. A second option would be a watertight external air shaft (there are also watertight light wells) with forced drainage including a backflow preventer.
What does the soil report say about the groundwater level and which load case applies? Is the design groundwater level of -1.75m (about -5.7 ft) already increased by a risk factor (usually 0.3m / 1 ft)? What does the soil report recommend for basement waterproofing? Presumably, waterproof concrete construction and watertight light wells and windows?
Overall, I see it as positive that your general contractor immediately raises concerns here instead of just blindly carrying on. I will call the manufacturer tomorrow and inquire.
Regarding the groundwater level: a test excavation has already been carried out, showing no water up to 3m (about 10 ft). In the borehole, water was found at -3.62m (about -12 ft). There is no mention of a risk factor.
The report also states the following: “Terrain cuts at the building, light wells, light trenches, or exposed external basement stairs must be permanently drained to be backflow-safe according to the plan. Alternatively, the ingress of rainwater and surface water can be prevented by covers or canopies.”
Baskervile schrieb:
"Before beginning the groundwork, the property must be examined for any unexploded ordnance from World War II by a certified bomb disposal service."
Statement from the local authority: "There is no known abstract or specific risk related to unexploded ordnance for this building site."
The property is an untouched meadow that was formerly used for agriculture and is located in Bavaria. The British took many aerial photographs before and after the bombings, which they now provide access to, although not directly available to the public. Analyzing these images here would require a long lead time of several months, and I believe the bomb disposal service has even longer waiting periods. A friend of mine had to have a located bomb removed (rented house, bomb deep and at the back of the garden), and I recall the waiting time was over six months.
I would try to use the statement from the local authority (preferably in writing) to challenge your building permit / planning permission.
Regarding the topic of unexploded ordnance:
Call the soil expert to find out if there is any specific suspicion concerning the plot of land. Otherwise, I could write this for any property. The cost-benefit ratio is usually quite poor, even for a suspected area. In Hesse, you can submit an inquiry to the Regional Council (KMRD), and they provide relatively inexpensive information about whether there is any suspicion at all. Unfortunately, I cannot say how this works in Bavaria.
About groundwater:
Please quote the passage regarding groundwater from the soil report. Assuming a fluctuation range of 2 meters (6.6 feet) for a groundwater level of -3.6 meters (11.8 feet) below ground level is quite optimistic. Generally, a range of ±1 meter (3.3 feet) is used.
Sealing the basement against hydrostatic pressure is, of course, essential.
Call the soil expert to find out if there is any specific suspicion concerning the plot of land. Otherwise, I could write this for any property. The cost-benefit ratio is usually quite poor, even for a suspected area. In Hesse, you can submit an inquiry to the Regional Council (KMRD), and they provide relatively inexpensive information about whether there is any suspicion at all. Unfortunately, I cannot say how this works in Bavaria.
About groundwater:
Please quote the passage regarding groundwater from the soil report. Assuming a fluctuation range of 2 meters (6.6 feet) for a groundwater level of -3.6 meters (11.8 feet) below ground level is quite optimistic. Generally, a range of ±1 meter (3.3 feet) is used.
Sealing the basement against hydrostatic pressure is, of course, essential.