Two distinct volumes that dialogue with the landscape – this design approach offers a powerful framework for residential architecture on open sites. The Groba House (Casa Groba) in Brasília, Brazil, demonstrates how a dual-volume strategy can respond to site context, separate public and private functions, and use structural systems tailored to each volume’s spatial requirements. Designed by Estúdio MRGB and completed in 2017, the 350 m² house sits on the characteristic flatlands of Brasília, a landscape defined by wide horizons and low-rise development. The architectural concept mirrors modern barn house compositions where distinct pavilions create a clear hierarchy between gathering and retreat spaces.
The Dual-Volume Concept in Residential Architecture
The Groba House organizes its program into two primary volumes. The main pavilion breaks with conventional residential morphology through an unconventional geometry that invites occupants to move between public and private domains separated only by a glazed plane. The secondary block, lower in scale, holds the family’s more private spaces with fewer openings and a stronger dialogue with the rear portion of the site and its vegetation. This clear window selection strategy – generous glazing on the public volume, restrained openings on the private one – reinforces the programmatic distinction at the building envelope level.
Hierarchy and Massing in Two-Volume Compositions
The relationship between the two volumes follows a deliberate hierarchy. The main pavilion commands attention with its higher roof line and bold geometric form. It houses the gathering spaces – living room, dining area, kitchen – where the family receives guests and spends daytime hours. The secondary block sits lower, its horizontality mimicking Brasília’s plains, containing bedrooms and studies. A glazed plane at the main pavilion’s perimeter is the only demarcation between the covered interior and the exterior landscape, creating a threshold that is visual rather than solid.
| Design Parameter | Main Pavilion | Secondary Block |
|---|---|---|
| Primary function | Gathering, dining, entertaining | Sleeping, study, private retreat |
| Structural system | Concrete porticos, inclined slabs | Inverted beams, columns, flat slabs |
| Envelope openness | Full-height glazed plane | Fewer, smaller openings |
| Spatial quality | Expansive, connected to landscape | Enclosed, introverted |
| Roof system | Inclined slabs + steel shingles | Conventional flat slab |
Concrete Portico Systems for Residential Spans
The main pavilion of the Groba House is structured by concrete porticos that span six meters. Six of these porticos are repeated at 4.60-meter intervals, forming the primary structural solution for the entire first block. A portico system differs from a standard beam-and-column frame in that each portico is a rigid frame – the columns and beam are monolithically connected, creating a moment-resisting unit that distributes lateral and gravity loads together. This system eliminates the need for shear walls or bracing within the volume, preserving the open floor plan that the design requires.
Portico Geometry and Repeat Intervals
The 6-meter span offers a generous clear width for an open-plan residential space. At this span, a concrete beam depth of approximately 400–500 mm is typical, depending on the superimposed load from the roof structure and any potential occupancy on an upper slab. The 4.60-meter interval between porticos creates a rhythmic bay structure that organizes the interior layout without requiring interior columns. Each bay becomes a natural zone within the open plan, allowing furniture layouts and activity areas to align with the structural grid.
- Span-to-depth ratio – a 6-meter span with a 450 mm beam depth gives a ratio of approximately 13:1, within the efficient range for reinforced concrete
- Portico interval – 4.60 meters provides adequate width for a living zone (sofa, coffee table, circulation) or a dining zone (table, chairs, sideboard) in each bay
- Portal action – the monolithic column-beam connection creates inherent lateral stiffness, resisting wind loads without additional bracing
- Formwork reuse – six identical porticos mean the formwork system is reused six times, reducing both cost and construction time
Longitudinal Stability and Diaphragm Action
The structural stability of the main pavilion is guaranteed by longitudinal beams in the upper floor’s slab plane and the inclined roofing slabs. These elements work together as a horizontal diaphragm, distributing lateral loads from wind or seismic events back to the porticos. This design approach is typical of showcase home construction where open volumes require creative structural solutions that balance transparency with stability. The longitudinal beams run perpendicular to the portico frames, tying all six frames together into a coherent three-dimensional structure.
Inclined Roof Slabs as Structural Elements
The inclined roofing slabs in the main pavilion serve multiple structural roles. They provide the sloped roof form that defines the pavilion’s distinctive geometry. They act as deep beams in their own plane, contributing to the longitudinal stiffness of the building. They support the steel shingles of the façade and roof covering. And they were carefully designed to create thermo-acoustic insulation when combined with the steel shingle system. The inclination also facilitates natural drainage in Brasília’s rainy season, eliminating the need for complex roof drainage systems.
| Structural Element | Function | Material | Span / Spacing |
|---|---|---|---|
| Concrete porticos | Primary gravity + lateral load resistance | Reinforced concrete | 6 m span × 4.60 m spacing |
| Longitudinal beams | Diaphragm action, frame tying | Reinforced concrete | Full building length |
| Inclined roof slabs | Roof form, deep beam, insulation base | Reinforced concrete | Variable pitch |
| Steel shingles | Weathering surface, thermal-acoustic layer | Galvanized steel | Continuous |
The Secondary Block: Inverted Beams and Conventional Construction
While the main pavilion adopts an unconventional construction system, the secondary block is built as a rigorous architectural piece using inverted concrete beams, columns, and slabs. This conservative structural approach suits the private program of bedrooms and studies, where smaller spans and lower ceiling heights are acceptable and desirable. The passive house design strategies of the secondary block emphasize thermal comfort through reduced glazing ratios and protected openings rather than the exposure strategies used in the main pavilion.
Inverted beams – beams that project above the slab rather than below it – create a flush ceiling surface that simplifies interior finishing and allows for a clean, uninterrupted ceiling plane. This detail is particularly valuable in bedrooms where exposed beam soffits might collect dust or feel visually intrusive. The inverted beam approach also conceals the slab edge at the roof level, creating a cleaner exterior profile for the lower volume. The columns in the secondary block are spaced more closely than the porticos, at approximately 3–4 meter intervals, reflecting the smaller room sizes and reduced span requirements.
Construction System Contrast within One Project
Using two different structural systems within a single project increases design complexity but delivers specific benefits. The main pavilion’s portico system provides the open, column-free space appropriate for social functions. The secondary block’s conventional frame provides the cost efficiency and simpler detailing appropriate for cellular rooms. The two systems meet at the transition between volumes, where expansion joints accommodate differential movement between the heavier main structure and the lighter secondary frame.
Thermo-Acoustic Roofing with Steel Shingles
The inclined concrete slabs of the main pavilion are finished with steel shingles that serve as both weatherproof cladding and a component of the building’s thermo-acoustic insulation strategy. Steel shingles over a concrete substrate create a layered roof assembly. The concrete slab provides mass, which absorbs and delays heat transfer. The air gap between the slab and the shingles allows ventilation that carries away heat absorbed by the steel surface. The steel itself reflects a portion of incoming solar radiation. This assembly addresses Brasília’s climate, where intense sun and seasonal heavy rains make thermal and acoustic performance critical. The approach parallels passive house remodeling techniques that upgrade existing roof assemblies with layered insulation and reflective surfaces to reduce cooling loads.
Heat Flow Through a Concrete-and-Steel Roof Assembly
- Steel shingle surface – reflects 30–50% of incident solar radiation depending on color and finish
- Ventilated air gap – moving air behind the shingles carries away absorbed heat before it reaches the concrete
- Concrete slab – 100–150 mm of concrete provides thermal mass, delaying peak heat transmission by 4–6 hours
- Interior finish – painted ceiling surface with moderate emissivity, comfortable for radiant heat exchange with occupants
Acoustic performance follows a similar layered principle. The mass of the concrete slab blocks airborne sound transmission. The steel shingles, while lighter, provide a first line of defense against rain impact noise. The combination achieves a sound transmission class (STC) rating estimated between 45–50, which is adequate for residential roof assemblies in single-family detached homes where aircraft or traffic noise is the primary concern.
Landscape Integration and Site Response
The Groba House’s dual-volume approach is not merely a formal exercise – it responds directly to the Brasília flatlands. The main pavilion breaks with the horizontal line of the plains through its upward geometry, creating a landmark on the site. The secondary block deliberately mimics the horizontality of its surroundings, anchoring itself to the landscape. The landscape design by Paola Liebhardt reinforces this dialogue, with planting that softens the transition between the built volumes and the open terrain. The rear portion of the site, with its existing vegetation, provides a natural backdrop for the private functions of the secondary block, while the front exposure of the main pavilion opens toward the street and the broader landscape.
This landscape-responsive approach has practical implications for site planning. The house occupies a relatively compact footprint for its 350 m² program, leaving generous areas of the site for outdoor use. The orientation of each volume was calibrated to Brasília’s solar path: the main pavilion’s full-height glazing faces away from the harshest afternoon sun, while the secondary block’s reduced openings minimize heat gain on the east and west exposures. These passive strategies reduce the energy required for cooling without adding mechanical complexity. The broader lessons from such ultra-low-carbon housing projects show that thoughtful site orientation and volume placement contribute significantly to a building’s overall energy performance over its lifespan.