Steeply sloped building sites require spatial strategies that ordinary flat lots do not. When the terrain drops sharply, the house must stack vertically rather than spread horizontally, and each level connects to the ground at a different elevation. A house built on an extreme hillside in the Bregenz Forest of Austria demonstrates how three-level organization, a top-floor entry sequence, and contrasting material choices between wood warmth and concrete mass can turn a steep slope constraint into a design advantage. The key lies in how architects drive passive house building envelope performance through material selection and orientation, principles that apply directly to sloped residential sites where every floor interacts with the ground differently.
Steep Slope Site Planning and Three-Level Organization
Building on a steep slope changes the fundamental organization of a house. Instead of entering at grade and moving horizontally through public to private spaces, the entry typically occurs at an upper level, and the house descends the slope. In the Sulzberg house, the site sits on the back ridge of a mountain in a densely built-up housing estate. The property is tightly dimensioned, so every square meter of floor area had to be used efficiently. The solution was to divide the 220-square-meter program across three floors that step down the slope.
The top level contains the public zones: garage, guest room, and the main living room with kitchen. This arrangement means the most-used spaces sit at street grade, requiring no stairs to reach from the entry. The middle floor holds the private bedroom suite, dressing room, bathroom, and sauna. The basement level accommodates a granny flat and an office, both opening to a covered garden terrace at ground level on the downhill side. This inverted program – public on top, private below – is a hallmark of design approaches that blend heritage conservation with passive house performance on constrained urban sites.
Floor-by-Floor Allocation for Hillside Homes
| Level | Position on Slope | Primary Functions | Ground Access | Typical Ceiling Height |
|---|---|---|---|---|
| Top floor | Street grade | Entry, living room, kitchen, garage, guest room | Direct from street via walkway | 2.6-3.0 m |
| Middle floor | Mid-slope | Master bedroom, dressing room, bathroom, sauna | Staircase from top floor, terrace at grade on south | 2.5-2.8 m |
| Lower floor | Downhill base | Granny flat, office, utility | Covered garden terrace at ground level | 2.4-2.7 m |
Site Constraints That Drive Vertical Stacking
Several specific conditions on steep slopes push designers toward vertical rather than horizontal plans:
- Building footprint limits: setback regulations and zoning envelope restrictions often cap the built area per floor
- Excavation costs: cutting a wide bench into the slope is expensive and disrupts drainage patterns
- View optimization: stacking floors allows each level to face the downhill direction for unobstructed views
- Thermal stratification: heat naturally rises, so placing bedrooms below living areas lets residual warmth drift up to the most-used spaces
Top-Level Entry and Open Living Space Design
Entering a hillside house at the top level creates an immediate connection between the street and the main living zone. In the Sulzberg house, a wide walkway leads from the street to the entrance on the top floor. The garage sits adjacent, so residents can move from car to house without climbing stairs. Once inside, the entire southern wall opens through floor-to-ceiling glazing onto a terrace that overlooks the Bregenzerwald valley and the high Vorarlberg mountains beyond.
The living room is designed for maximum transparency and openness. A free-standing kitchen block is the only interior element that organizes the space, separating the cooking zone from the lounge area without enclosing either. This layout relies on the kitchen island or peninsula as a room divider rather than walls, keeping the visual connection from the entry through to the view uninterrupted. The south-facing terrace extends the living space outdoors, effectively doubling the social area during warm weather.
Key design features of the top-level living zone include:
- Full-width glazing with minimal mullions to maximize the view corridor
- A free-standing kitchen block that defines zones without blocking sight lines
- A terrace at the same level as the interior floor, creating a seamless indoor-outdoor transition
- Deep roof overhangs or an upper-floor projection to shade the south glazing in summer
Vertical Circulation and Private Zone Design
A cantilevered wooden staircase connects the top-level public zone to the private rooms on the middle floor. The staircase becomes a sculptural element in its own right, cantilevering from the wall without visible supports. This open-tread design maintains visual permeability between levels, so the stairs do not block light or views. At the middle level, the bedroom, dressing room, bathroom, and sauna form a suite clad entirely in silver fir, creating a warm, enclosure-like atmosphere.
The contrast between the open, glass-enclosed top level and the enclosed, wood-lined private level is intentional. Each room on the middle floor is described as being like a wooden casket – intimate spaces that provide privacy and acoustic separation from the rest of the house. This layering of open and enclosed spaces connects passive house heritage conservation with high-performance design, where the thermal envelope is continuous but the interior atmosphere changes between public and private zones.
Staircase Design for Hillside Homes
The staircase in a multi-level hillside house must function well and also serve as a visual and structural connector between floors. Design considerations include:
- Cantilevered treads: each tread anchors into a structural wall, eliminating the need for stringers or a central spine and keeping the stair visually light
- Open risers: gaps between treads allow light to pass through and reduce the visual mass of the stair
- Material consistency: using the same wood species as the interior cladding ties the stair to the surrounding finishes
- Handrail integration: glass or thin metal railings preserve transparency while meeting building code requirements
Material Contrast: Wood Warmth and Concrete Mass
The material palette of the Sulzberg house relies on a deliberate contrast between warm, organic wood and cool, massive concrete. The two lower floors are built from exposed concrete in rough board formwork, giving the walls a textured surface that records the grain of the timber forms used during pouring. The roof structure, by contrast, is timber framed. This split – concrete below, wood above – follows the functional logic of the site: the lower floors are partly embedded in the slope and need moisture-resistant construction, while the upper floors benefit from wood’s lighter weight and better thermal performance.
Inside, the material contrast continues. Concrete walls on the lower levels give way to silver fir cladding on the middle floor and a blend of wood and glass on the top level. The interior floor is primarily ash, and furnishings are made from silver fir. This strategy of using material distinction to organize interior space aligns civic design with passive house principles, where the material speaks to the function of each zone.
Material Performance by Elevation
| Elevation Zone | Structural Material | Interior Finish | Moisture Risk | Thermal Mass Benefit |
|---|---|---|---|---|
| Lower floor (embedded) | Exposed concrete, board formwork | Exposed concrete | Moderate to high | High (ground-coupled) |
| Middle floor (mid-slope) | Exposed concrete walls | Silver fir cladding | Low | Moderate (internal walls) |
| Upper floor (above grade) | Timber frame roof | Silver fir, glass, ash flooring | Low | Low (roof insulation above) |
Board formwork concrete creates a distinctive surface pattern that architects often specify when they want the construction process to remain visible in the finished building. The horizontal grain of the formwork boards contrasts with the vertical white fir strips on the facade, creating a play of directional lines that emphasizes the geometric, disc-like composition of the house.
Privacy and Shading Strategies for Transparent Facades
Floor-to-ceiling glazing on the south facade creates a potential privacy problem on a densely built site. The Sulzberg house solves this with slidable wooden slats mounted on the side fronts. These slatted screens can be positioned to block sight lines from neighboring houses without reducing the view straight ahead. The slats function as adjustable louver systems: when closed, they provide visual privacy and sun protection; when open, they disappear into the facade, restoring the fully transparent elevation.
The combination of slatted wood screens and roof overhangs gives the house three layers of environmental control:
- Primary: roof overhang and balcony projection shade the upper portion of the glazing
- Secondary: slidable wooden slats provide adjustable shading at the occupant’s control
- Tertiary: interior blinds or curtains offer final light-level adjustment for glare or sleeping areas
On the street side, the house presents a relatively closed elevation. The entrance and garage are the only openings on the north facade, reducing heat loss and providing a clear public-private transition. The architect’s role in passive house design includes managing these transitions between public and private, open and closed, transparent and opaque. The street facade of the Sulzberg house reads as a solid cubic volume, while the garden side is almost entirely glass. This duality – closed on the uphill side, transparent on the downhill side – is an effective strategy for integrating passive house standards with sustainable urban architecture on hillside sites where every floor demands a different relationship to the ground and the view.