Installation shaft – why it is a game-changer in modular houses
In a specification, it sounds unremarkable: "installation shaft 4–6 cm." No customer gets excited about that line at purchase. But in 15–20 years, this solution can save tens of thousands and weeks of renovation. We explain what the shaft is, why Treevia uses it, and how it changes the ownership experience.
What is an installation shaft?
The installation shaft is a dedicated 4–6 cm space between the PE vapour barrier film and the plasterboard (GK). This is where you find:
- Electrical wiring (cables, sockets, switches)
- Plumbing pipes (water, concealed drainage)
- Possible telecommunications and smart home cables
Critically: the shaft is separated from the thermal envelope by PE film. Installations do not pass through insulation or the vapour barrier membrane.
How it looks in practice – wall construction
Full Treevia wall cross-section (from outside):
- Timber cladding 20–28 mm or render
- Ventilated air gap 30 mm
- Dörken Delta-Vent S+ membrane
- Mineral wool 75 mm (external batten)
- OSB/3 12 mm
- Mineral wool 150 mm+ (C24 structure)
- OSB/3 12 mm
- Mineral wool 50 mm
- PE film (vapour barrier, sd = 20 m)
- OSB/3 12 mm
- Installation shaft 4–6 cm ← installations go here
- Plasterboard 12.5 mm
Note the PE film position (layer 9): it is before the shaft, on the insulation side. This means every shaft operation – socket mounting, cable routing, pipe replacement – happens without breaching the vapour barrier.
What about standard houses?
In a typical timber-frame house (without a shaft), installations run inside the structural wall – between insulation layers, through holes in the PE film. Consequences:
During construction:
- Every socket requires piercing the PE film
- Tape sealing of holes is a compromise – it will never be as airtight as continuous film
- Installer and builder must coordinate – risk of execution errors
In 15–20 years:
- Rewiring = breaking walls
- Breaking = destroying mineral wool at the work site
- Destroyed wool = thermal bridge (a point where the wall loses insulation performance)
- PE film breach = uncontrolled water vapour flow → condensation risk → mould
- Cost: PLN 20,000–50,000 + weeks of renovation + mess
This is not theory. This is the standard scenario for installation upgrades in timber houses after 15–20 years of use.
What does the shaft deliver over 30 years?
Year 0–5: Invisible
The shaft is hidden behind plasterboard. You cannot see or feel it. The house works normally.
Year 5–10: First modifications
Want to add a kitchen socket? An extra light point? With a shaft, it is a few hours' work – open GK, route cable, close. Without a shaft: break wall, patch insulation, restore PE film.
Year 10–15: Smart home upgrade
Smart home systems evolve every 5 years. Adding sensors, wiring, control modules in the shaft is a simple adaptation. In a structural wall – an invasive renovation.
Year 15–20: Installation replacement
Electrical standards change. 20-year-old wiring may not meet new requirements. Replacement in a shaft: PLN 3,000–8,000, a few days. Without a shaft: PLN 20,000–50,000, several weeks.
Year 20–30: Lasting property value
A house with easily serviceable installations retains market value. A house where every upgrade means costly renovation loses attractiveness.
Why do other manufacturers not use a shaft?
Three reasons:
- Cost: the shaft adds 4–6 cm to wall thickness – more material, more labour, higher price. In the race for the lowest "from..." price, every centimetre counts
- Production complexity: the shaft requires an additional OSB layer and precise batten installation. This complicates the production line
- The customer cannot see it: in a house photo, the shaft is invisible. It does not sell like "modern kitchen" or "panoramic windows"
Treevia treats the shaft as an engineering element, not a marketing one. It does not appear in the hero photo, but it appears in thermal calculations and operating costs over 30 years.
PE film in the optimal position
The shaft affects not just servicing – it also affects wall building physics.
In Treevia construction, the PE film is placed after the 50 mm internal wool (layer 8) and before the OSB and shaft (layers 10–11). This is the optimal position:
- Water vapour from the interior hits the PE film before reaching insulation
- Insulation stays dry – no condensation
- The shaft and GK are on the "warm" side of the film – they do not affect the dew point
In houses without a shaft, the PE film is directly under GK. Every socket, every switch pierces the film. Every piercing is a potential condensation point years later.
Summary
The 4–6 cm installation shaft means:
- Separating installations from the thermal envelope – servicing without disturbing insulation
- Preserving PE film continuity – no condensation points
- Saving PLN 15,000–45,000 on installation upgrades over 20–30 years
- Flexibility – easy addition of sockets, smart home, new points
4–6 centimetres that make no impression in a photo but make an enormous difference over decades of use.