Hello everyone,
Short version: We moved into our newly built house in 2022 and experienced regular sewage odors inside the house just a few months later. Our building partner has not been able to resolve this issue to date. The odors are mainly noticeable during humid weather and when there is slight negative pressure inside the house.
Key facts related to the issue:
- KFW55 energy-efficient house
- Two-family house with two separate controlled mechanical ventilation systems (reco boxx 310)
- Wastewater lifting station (greywater) in the utility room, recently cleaned (no improvement)
- All traps checked, none are dry, and all are regularly used
Detailed history
2022/2023 – Shortly after moving in 2022, we quickly noticed sewage odors throughout the entire house. I personally observed that the roof vent stacks were only about 1 meter (3 feet) away from the fresh air intake of the ventilation system, and suspected this was the cause of the odor issue. The plumber then changed the fresh air intake and exhaust arrangement, with fresh air now coming from the side of the house at 2 meters (6.5 feet) height and exhaust going through the roof. This significantly reduced the odors in the entire house but did not completely eliminate them.
During warm summer weather, the odor was still present, especially in the utility room (basement) and in the guest bathroom (directly above the utility room, where the vertical soil pipes, vents, etc., run through a boxed-in section).
Since we have a room-sealed fireplace with a pressure monitor, I can detect the pressure difference between inside and outside the house. The odors appear mainly when there is negative pressure inside the house. This happens, for example, when I operate a monoblock air conditioner without using the two-duct mode, or when I set the controlled mechanical ventilation system to exhaust-only mode. I often do the latter in the summer evenings, opening only the bedroom windows, so that all the air being drawn out enters the house through the bedroom window. This quickly creates a comfortable temperature when it has been too warm during the day. However, this also increases the odors. We are talking about pressure differences of between 1 - 4 Pascal.
2023/2024 – After the first attempt failed to solve the problem, the ventilation curves of the mechanical ventilation systems were adjusted (exhaust slightly reduced, fresh air increased) to prevent negative pressure. Unfortunately, this attempt also did not produce any results.
2024/2025 – Since the smell persisted, a camera inspection was performed behind the toilets, revealing a “displaced seal” in a wastewater pipe. Tiles were removed, the seal replaced, and tiles reinstalled. This work was done in February 2025, and we were initially optimistic since the technician said, “I immediately smelled a musty odor, that was definitely it.” Unfortunately, that was not the case. The smell of rotten eggs or old sewage water is currently present again in this hot weather.
I have now submitted another formal complaint to our construction company, but I feel stuck and wanted to ask here if anyone has ideas what might be causing this.
Important details: What I noticed early on and informed our plumber about is that when I pour something strongly smelling into the toilet on the upper floor (chlorine cleaner during cleaning), I immediately smell it in the utility room in the basement. I have little experience in plumbing, but this should not be normal, right? To me, this clearly indicates a leak in the wastewater pipe when odors from the upper floor wastewater can be smelled in the basement utility room, and only here and in the ground floor bathroom. Not in the living room or hallway – so no distribution via the mechanical ventilation system.
Other odors from the toilet can also be smelled in the utility room when someone is using the toilet upstairs.
I would really appreciate any input on where to start because I am truly getting desperate. The house regularly smells so bad that we do not want to receive guests.
Attached are some pictures of the area that was opened and the faulty seal in a pipe joint that was replaced.
Thank you!
Best regards,
Markus
Short version: We moved into our newly built house in 2022 and experienced regular sewage odors inside the house just a few months later. Our building partner has not been able to resolve this issue to date. The odors are mainly noticeable during humid weather and when there is slight negative pressure inside the house.
Key facts related to the issue:
- KFW55 energy-efficient house
- Two-family house with two separate controlled mechanical ventilation systems (reco boxx 310)
- Wastewater lifting station (greywater) in the utility room, recently cleaned (no improvement)
- All traps checked, none are dry, and all are regularly used
Detailed history
2022/2023 – Shortly after moving in 2022, we quickly noticed sewage odors throughout the entire house. I personally observed that the roof vent stacks were only about 1 meter (3 feet) away from the fresh air intake of the ventilation system, and suspected this was the cause of the odor issue. The plumber then changed the fresh air intake and exhaust arrangement, with fresh air now coming from the side of the house at 2 meters (6.5 feet) height and exhaust going through the roof. This significantly reduced the odors in the entire house but did not completely eliminate them.
During warm summer weather, the odor was still present, especially in the utility room (basement) and in the guest bathroom (directly above the utility room, where the vertical soil pipes, vents, etc., run through a boxed-in section).
Since we have a room-sealed fireplace with a pressure monitor, I can detect the pressure difference between inside and outside the house. The odors appear mainly when there is negative pressure inside the house. This happens, for example, when I operate a monoblock air conditioner without using the two-duct mode, or when I set the controlled mechanical ventilation system to exhaust-only mode. I often do the latter in the summer evenings, opening only the bedroom windows, so that all the air being drawn out enters the house through the bedroom window. This quickly creates a comfortable temperature when it has been too warm during the day. However, this also increases the odors. We are talking about pressure differences of between 1 - 4 Pascal.
2023/2024 – After the first attempt failed to solve the problem, the ventilation curves of the mechanical ventilation systems were adjusted (exhaust slightly reduced, fresh air increased) to prevent negative pressure. Unfortunately, this attempt also did not produce any results.
2024/2025 – Since the smell persisted, a camera inspection was performed behind the toilets, revealing a “displaced seal” in a wastewater pipe. Tiles were removed, the seal replaced, and tiles reinstalled. This work was done in February 2025, and we were initially optimistic since the technician said, “I immediately smelled a musty odor, that was definitely it.” Unfortunately, that was not the case. The smell of rotten eggs or old sewage water is currently present again in this hot weather.
I have now submitted another formal complaint to our construction company, but I feel stuck and wanted to ask here if anyone has ideas what might be causing this.
Important details: What I noticed early on and informed our plumber about is that when I pour something strongly smelling into the toilet on the upper floor (chlorine cleaner during cleaning), I immediately smell it in the utility room in the basement. I have little experience in plumbing, but this should not be normal, right? To me, this clearly indicates a leak in the wastewater pipe when odors from the upper floor wastewater can be smelled in the basement utility room, and only here and in the ground floor bathroom. Not in the living room or hallway – so no distribution via the mechanical ventilation system.
Other odors from the toilet can also be smelled in the utility room when someone is using the toilet upstairs.
I would really appreciate any input on where to start because I am truly getting desperate. The house regularly smells so bad that we do not want to receive guests.
Attached are some pictures of the area that was opened and the faulty seal in a pipe joint that was replaced.
Thank you!
Best regards,
Markus
Eliatuer schrieb:
I just listened to the episode "Incense Stick Affair." Definitely amusing 🙂 The older couple lives next door to us, but I know them well. They are my parents-in-law, our two household units are connected through the utility rooms (connecting door), and the smell is only coming from our side. I can rule out their side. Family Moppermann are your parents-in-law? Right?