ᐅ Questions About the Wall Construction of a 1998 Stelly Prefabricated House

Hello
I have recently been offered a property for purchase that I like very much.
It is a Stelly prefabricated house from 1998. In 2001, Stelly was acquired by Talbau-Haus.
Since I have read quite a bit online, including many negative things about the wall constructions of prefabricated houses, I wanted to ask here. I have the full construction description. Can you tell me if the construction/quality is acceptable for a prefab house? How is the sound insulation in these walls? Should I be concerned about musty odors from moisture in the walls at some point, and how long does a house like this typically last?
Exterior walls:
Total wall thickness 250mm (U-value 0.235 W/m2K)
3.00mm seamless synthetic resin plaster applied with a trowel over
3.00mm reinforcing plaster (total thickness approx. 6mm)
40.00mm special insulating construction boards -> (whatever this is – any idea?)
13.00mm wood-based panel V 100 G
165.00mm solid wood beams – frame construction made of dried high-quality softwood
150.00mm stiffened mineral wool insulation within the frame construction
13.00mm wood-based panel V 20 E1
0.20mm foil as a vapor barrier
12.50mm natural gypsum boards
Interior walls:
Sound and thermal insulated, particularly stable, with no restrictions for attaching shelves and cabinets on any wall. Total wall thickness 151mm
12.50mm natural gypsum boards
13.00mm wood-based panel V 100 G
100.00mm solid wood beams – frame construction made of dried high-quality softwood
100.00mm stiffened mineral wool insulation within the frame construction
13.00mm wood-based panel V 100 G
12.50mm natural gypsum boards
Floor ceilings between storeys:
Impact sound insulated ceilings with 220mm thick solid wood beams, total thickness depending on the finishing stage up to 400mm
Assembly from top to bottom:
25.00mm wood-based panel V 100 G
220.00mm solid wood beams – statically calculated, made of dried high-quality softwood
120.00mm stiffened mineral wool insulation within the frame construction
0.20mm foil as a vapor barrier
20.00mm substructure of dried softwood
12.50mm natural gypsum boards

Thank you very much and best regards

Thomas

We have owned a Stelly house since 1996, so I can answer this question. During the construction phase, there were several issues, and afterwards some defects appeared that seem typical for prefab houses. For example, the four exterior corners in the attic were not watertight, and a lot of expanding foam had to be used to fix this. The load-bearing wall on the ground floor was partly installed crookedly (it consists of two parts). The roof had to be taken off and redone because the scaffolding builder (a local master roofer) identified serious installation errors.

The theoretical values for thermal insulation are calculated based on a wall without corners, windows, doors, or floor and ceiling connections. Defects such as gaps in corners or missing silicone seals around the windows are naturally not taken into account.

Sound insulation is significantly worse compared to a solid house. This is mainly due to the difference in wall mass, so the two are not comparable. The sound insulation inside the house is acceptable, thanks to the screed.

My conclusion: Never again a prefab house, never again let a distant company build a house.

In my current view, the advantages of prefab houses (fast construction time, low rental and financing costs) are far outweighed by the disadvantages.