ᐅ New Construction of a Semi-Detached House / Insulation Solution for the Gap Between Units
Created on: 1 Oct 2025 17:31
P
pfrieder
Dear Forum,
We are currently planning the construction of a semi-detached house. The demolition has already been completed, and winter is approaching. The new timber frame house (prefabricated, KfW40 standard) is expected to be installed by the end of February. The plan was different initially; the house should have been built already, but that is another issue.
The neighbor has asked us to install insulation on the remaining party wall, since it will no longer be heated on our side. The wall is currently protected against rain with a foil. The existing building, built in 1942, has a partial basement and 1.5 stories. Only the upper two floors need insulating. At some point around 1986, the existing building was fitted with external insulation of about 4cm (1.5 inches).
The party wall structure from inside to outside on the upper two floors is as follows:
The prefab company says that nothing needs to be done here; just place the house in front, and that’s fine. However, I have doubts regarding the thermal protection for the neighbor. There isn’t much room left for effective insulation, but from my point of view, possible solutions could be:
We are now looking for an affordable solution that bridges the winter period but also avoids any long-term deterioration for the neighbor.
Best regards
We are currently planning the construction of a semi-detached house. The demolition has already been completed, and winter is approaching. The new timber frame house (prefabricated, KfW40 standard) is expected to be installed by the end of February. The plan was different initially; the house should have been built already, but that is another issue.
The neighbor has asked us to install insulation on the remaining party wall, since it will no longer be heated on our side. The wall is currently protected against rain with a foil. The existing building, built in 1942, has a partial basement and 1.5 stories. Only the upper two floors need insulating. At some point around 1986, the existing building was fitted with external insulation of about 4cm (1.5 inches).
The party wall structure from inside to outside on the upper two floors is as follows:
- Interior plaster
- 240mm (9.5 inches) pumice concrete blocks
- Interior plaster
The prefab company says that nothing needs to be done here; just place the house in front, and that’s fine. However, I have doubts regarding the thermal protection for the neighbor. There isn’t much room left for effective insulation, but from my point of view, possible solutions could be:
- Blown-in insulation
- Thin insulation boards on the existing wall
- Insulating plaster on the existing wall
- Mineral wool joint insulation board (is it still possible to fit this behind? The entire wall will be plastered as one panel in front, right?)
We are now looking for an affordable solution that bridges the winter period but also avoids any long-term deterioration for the neighbor.
Best regards
Hi,
The dew points should be fine (actually in almost all cases), as long as I entered everything correctly in Ubakus.
The issue with the membrane and trapped moisture might be a problem, which is why I have also looked into laminated panels, but that becomes tricky again because of their susceptibility to denting in case it doesn’t fit perfectly.
The neighboring building is made entirely of pumice concrete blocks from bottom to top, while only the new house will be timber frame.
The dew points should be fine (actually in almost all cases), as long as I entered everything correctly in Ubakus.
The issue with the membrane and trapped moisture might be a problem, which is why I have also looked into laminated panels, but that becomes tricky again because of their susceptibility to denting in case it doesn’t fit perfectly.
The neighboring building is made entirely of pumice concrete blocks from bottom to top, while only the new house will be timber frame.