Treevia wall cross-section – 12 layers that protect your home
An exterior wall is not just a barrier between inside and outside. It is a complex engineering partition that determines thermal comfort, structural durability, and heating bills for the next 30 years. In this article, we break down the Treevia wall layer by layer.
Why wall thickness matters
The Treevia exterior wall is 52 cm thick in total, including the installation shaft and double plasterboard finish. That is significantly more than a typical timber-frame wall (28–30 cm), but every centimetre serves a specific function.
The result? U-value of 0.15 W/(m²K) – 25% better than the WT 2021 standard. Zero condensation in any layer. 11-hour phase shift. 17× temperature amplitude damping.
12 layers – from outside to inside
Layer 1: Timber cladding 20–28 mm or render
The outer façade finish. Timber cladding creates a ventilated façade – circulating air behind it removes moisture and protects deeper layers. Alternatively, a base render can be applied.
Layer 2: Ventilated air gap 30 mm
A critical element missing from many timber-frame houses. The 30 mm air gap acts as a buffer – it removes moisture from the façade and protects the membrane for decades. Without this gap, render or cladding directly on the membrane shortens its lifespan.
Layer 3: Dörken Delta-Vent S+ membrane
A high-diffusion vapour-permeable membrane. It allows water vapour to escape outward but blocks water and wind from entering. Dörken Delta-Vent S+ is a premium product used in buildings with elevated requirements.
Layer 4: Mineral wool 75 mm (external batten)
The first layer of thermal insulation on a dedicated external batten. This is an additional 75 mm of insulation that typical timber-frame houses simply lack – they have one layer of insulation instead of three.
Layer 5: OSB/3 12 mm
The first of three OSB boards in the partition. It provides structural bracing and serves as a substrate for subsequent layers.
Layer 6: Mineral wool 150 mm+ (C24 structure)
The main insulation layer between C24-grade structural timber studs spaced at 600 mm. Standard lambda: λ = 0.035 W/mK, optional λ = 0.033 W/mK. Minimum insulation thickness is 15 cm.
Layer 7: OSB/3 12 mm
The second OSB board – closing the main insulation cavity from the interior side.
Layer 8: Mineral wool 50 mm
The third insulation layer. In total, three independent layers of mineral wool (75 + 150+ + 50 mm) eliminate thermal bridges and ensure insulation continuity.
Layer 9: PE film (vapour barrier, sd = 20 m)
Vapour barrier placed in the optimal position – after the internal wool, before the OSB board and shaft. This location follows building physics: it protects insulation from interior water vapour while allowing controlled drying outward.
Layer 10: OSB/3 12 mm
The third OSB board – providing a substrate for the installation shaft and additional bracing.
Layer 11: Installation shaft 4–6 cm
A defining feature of Treevia construction. A dedicated space for electrical and plumbing installations. Cables, pipes, sockets – everything runs in the shaft, not in the structural wall. Consequences:
- Installation and servicing without disturbing insulation
- Future upgrades without breaking walls
- Continuous vapour barrier membrane preserved
- In 15–20 years, rewiring is a matter of hours, not weeks
Layer 12: Plasterboard 12.5 mm
Interior finish – ready for painting, wallpapering, or tiling.
Three insulation layers vs one – why it matters
A typical timber-frame house has one layer of mineral wool (e.g. 180 mm) between studs. The problem? Timber studs have poorer insulation properties than wool – they create thermal bridges wherever a stud stands.
Treevia uses three independent insulation layers (75 + 150+ + 50 mm) on three different battens. The layers overlap, eliminating thermal bridges. Result:
- Better U-value at comparable thickness
- More uniform temperature distribution across the wall surface
- Zero condensation – confirmed by ubakus calculations at −20°C / 80% humidity
11-hour phase shift – what it means in practice
When July temperatures reach 35°C at 2:00 PM, the heat wave reaches the interior only at 1:00 AM – when it is already 18–20°C outside. The wall naturally "buffers" the heat.
17× amplitude damping means a 30°C temperature swing outside translates to just ~1.5°C inside. In practice: the house stays naturally cool in summer without air conditioning.
With increasingly hot Polish/European summers (35–40°C is no longer rare), this parameter gains value every year.
The installation shaft – the unsung hero
When receiving a new house, nobody notices the installation shaft. But in 15–20 years, when you need to:
- Replace electrical wiring
- Upgrade plumbing
- Add new socket points
- Change interior layouts
...a 4–6 cm shaft is the difference between a simple replacement costing a few thousand and a costly renovation costing €5,000–12,000 with wall-breaking, insulation damage, and vapour barrier destruction.
In houses without a shaft, every installation intervention means breaching the thermal envelope. Once pierced, PE film will never be as airtight as the original.
Parameter summary
- Wall thickness: 52 cm including installation shaft and 2× plasterboard
- Wall U-value: 0.15 W/(m²K) – 25% better than WT 2021
- Condensation: zero in any layer (ubakus calculations −20°C / 80%)
- Phase shift: 11 hours
- Amplitude damping: 17× (30°C outside = ~1.5°C inside)
- Structure: C24 timber, studs at 600 mm
- Membrane: Dörken Delta-Vent S+ (high-diffusion)
- Insulation: 3 layers of mineral wool on independent battens
Every layer serves a specific function. Nothing is accidental – this is engineering, not marketing.