Prefabricated wood construction offers a compelling approach to multi-family housing that combines speed of assembly, material sustainability, and design precision. The method involves manufacturing building components in a controlled factory environment and transporting them to the site for assembly, reducing construction time and minimizing waste. A well-documented example of this approach is a 1,480 cubic meter duplex in Switzerland, built using prefabricated wood panels for walls and slabs, clad in untreated Nordic larch, and finished with natural wood interiors. This article examines the key construction methods and material choices that define prefabricated wood duplex housing.
Understanding Prefabricated Wood Building Systems
Prefabricated wood construction falls into several categories depending on the size and type of components used. Panelized systems use wall, floor, and roof panels built in a factory and assembled on site. Modular systems use fully finished room-sized volumes. For duplex housing, panelized systems offer the best balance of customization and efficiency. The structural components, including load-bearing walls and floor slabs, are built from engineered wood products such as cross-laminated timber or glued laminated timber.
Key Advantages of Prefabrication
- Factory-controlled conditions eliminate weather-related delays and moisture exposure during construction
- Precision cutting and assembly reduce material waste by up to 20 percent compared to site-built framing
- Shorter construction timelines, with on-site assembly typically taking weeks rather than months
- Improved thermal performance due to tighter joints and consistent insulation installation
The duplex referenced in this article measures 24.10 meters in length, 6.60 meters in width, and 6.00 meters in height, with a total cubic volume of 1,480 cubic meters. These dimensions reflect efficient spatial planning that maximizes usable floor area while keeping the building footprint compact. The building envelope, including both walls and roof slabs, is constructed entirely from prefabricated wood elements, demonstrating the viability of wood as a primary structural material for multi-family housing.
Panel Types and Their Applications
| Panel Type | Typical Thickness | Primary Application |
|---|---|---|
| Cross-laminated timber (CLT) | 100 to 300 mm | Load-bearing walls and floor slabs |
| Glued laminated timber (glulam) | Varies by span | Beams, columns, and long-span roofs |
| Timber frame panels | 140 to 200 mm | Non-load-bearing walls and partitions |
| Structural insulated panels (SIPs) | 150 to 300 mm | Exterior walls with integrated insulation |
Structural Design with Prefabricated Wood Panels
The structural design of a prefabricated wood duplex requires coordination between architects, civil engineers, and wood engineers from the earliest stages. Unlike steel or concrete structures, wood panels must account for shrinkage, creep, and moisture response over the building’s lifespan. The duplex project involved a dedicated wood engineer, a civil engineer for structural calculations, and an RVS engineer for reinforcement and connection detailing.
Walls and slabs in prefabricated wood construction serve as both structural and finish elements. The interior face of the slab in this duplex was left exposed, with the natural wood surface serving as the ceiling finish. This approach eliminates the need for additional ceiling materials and reduces the overall material count. The mock-up installation techniques used in high-performance housing demonstrate how prefabricated wood panels are tested and verified before full-scale assembly.
Load Distribution and Connection Design
Load distribution in wood panel construction differs from traditional framing. Vertical loads from upper floors transfer through the panels directly to the foundation. Horizontal loads from wind and seismic activity are managed through diaphragm action of the floor and roof panels, which distribute forces to shear walls. Connection points between panels use metal brackets, screws, and engineered fasteners designed to accommodate wood movement while maintaining structural integrity.
- Foundation anchors are installed with precise tolerance to match panel connection points
- Ground-floor wall panels are craned into position and temporarily braced
- Floor panels are placed on top of wall panels and secured with metal brackets
- Upper-floor wall panels are stacked and connected, repeating the process to the roof
Exterior Cladding with Nordic Larch
The exterior cladding of a prefabricated wood duplex serves as the primary weather barrier and defines the building’s visual character. Nordic larch was chosen for the duplex discussed here, applied as untreated vertical boards. Larch is naturally resistant to decay and insect damage due to its high resin content, which allows it to weather without chemical treatments. Over time, untreated larch develops a silver-grey patina that many architects and homeowners find desirable, though the color shift should be anticipated during the design phase.
Board Dimensions and Installation
The larch boards used in this project measure 6 meters in full height and 9 centimeters in width. The consistent board width was used as a modular unit throughout the project, informing window placement and facade proportions. Boards are oriented vertically, which emphasizes the building’s height and creates clean, uninterrupted lines along the facade.
- Vertical board orientation promotes water runoff and reduces moisture entrapment
- A 5 to 10 millimeter gap between boards allows for natural expansion and contraction
- Stainless steel or galvanized fasteners prevent corrosion staining on the untreated wood
- A ventilated rain screen behind the cladding allows air circulation that dries any moisture that penetrates the board joints
Using the board size as a design unit creates visual rhythm across the facade. Windows are placed at intervals that correspond to multiples of the 9-centimeter module, producing a facade that reads as intentional and ordered. This modular approach extends naturally from the prefabrication method itself, where off-site manufacturing rewards dimensional consistency.
Large Windows and Indoor-Outdoor Spatial Flow
One of the defining features of well-designed prefabricated wood housing is the integration of large windows that connect interior spaces to the surrounding environment. The duplex uses full-height square windows that allow abundant natural light to penetrate deep into the living areas. A covered porch serves as a transitional space between indoors and outdoors, providing shelter from rain and sun while maintaining visual connection to the landscape.
The relationship between inside and outside was a central design consideration. Visual continuity between the day area and the external space is expressed through the large windows and the generous porch. This approach requires careful structural planning because large openings in load-bearing wood panels must be reinforced with lintels or engineered beams to maintain structural performance.
Window-to-Wall Ratio Considerations
The window-to-wall ratio directly affects both the building’s energy performance and its interior comfort. Higher ratios admit more solar heat gain in winter but increase heat loss in cold climates. For prefabricated wood buildings in temperate European climates, a window-to-wall ratio between 25 and 35 percent on south-facing elevations balances daylighting with thermal performance. The large square windows typical of this duplex design approach fall within this range when distributed across the facade.
The porch, measuring the full width of the building footprint, extends the usable living area into the outdoors. Covered but open on one side, it functions as an outdoor room that expands the perceived size of the ground-floor living space. The floor plan shows how the porch aligns with the main living area, creating a seamless indoor-outdoor flow that doubles the living space during warm months.
Interior Finishes and Material Palette
The interior finish strategy in prefabricated wood housing takes advantage of the structural materials themselves. Wood-block flooring provides a warm, durable surface for all horizontal planes. The inferior face of the upper floor slab is left exposed, with the natural wood serving as the ceiling finish for the room below. White paint on all vertical surfaces, including interior walls and the exposed structural columns, creates brightness and contrast against the wood tones.
The material palette follows a clear rule: horizontal surfaces are wood, vertical surfaces are white. This distinction creates a coherent visual language throughout the building. The wood-block flooring provides texture and warmth underfoot, while the white walls reflect natural light from the large windows deeper into the interior. The white vertical surfaces also make the wood ceiling and floor stand out as deliberate design elements rather than default finishes.
- Wood-block flooring is installed over the structural slab with an acoustic underlayment to reduce impact noise transmission between floors
- The exposed slab ceiling requires careful coordination of electrical and mechanical routing before panel installation
- White vertical surfaces are painted directly onto the wood panel surface, which must be properly prepared to prevent grain raise and uneven absorption
- All horizontal and vertical surface transitions use flush detailing rather than trim, maintaining the clean aesthetic that prefabricated construction enables
Planning and Engineering for Prefabricated Wood Homes
A prefabricated wood duplex requires coordination among multiple engineering disciplines from the project’s inception. The project team included an architect, a landscape architect, a civil engineer, a wood engineer, an RVS engineer for reinforcement and connection systems, and a fire engineer. Each specialist contributes to decisions that affect the prefabrication process, from panel dimensions to fire resistance ratings.
The fire engineer evaluates the wood structure against local building codes, which often require specific fire resistance ratings for multi-family residential buildings. Engineered wood products such as CLT char at a predictable rate when exposed to fire, maintaining structural integrity for longer than unprotected steel. This charring behavior is well documented and accepted by most building codes when proper calculations are submitted.
The landscape architect works with the building orientation to ensure that the large windows face desirable views and that the porch connects to usable outdoor space. The wood company responsible for manufacturing the panels coordinates with the design team during the detailing phase to ensure that every panel connection, window opening, and service penetration is accounted for before factory production begins. This level of coordination demands a complete set of construction documents before any manufacturing starts, which is a shift from traditional on-site construction where changes can be made during the build. Prefabricated wood construction offers a repeatable, high-quality method for duplex housing that delivers precision, speed, and natural material aesthetics in a single integrated package.