Across the outskirts of cities like Bogotá, and in temperate zones worldwide, more second homes rise as rural retreats for urban dwellers. This wave of construction presents an opportunity for architects, but also a significant challenge: each new building alters the rural landscape, strains local resources, and risks eroding vernacular building traditions. The Clap House in Apulo by AGRA Arquitectos offers a compelling counterexample. Sited on a west-facing hillside with views of the Eastern Cordillera of Colombia, it returns to the values of local vernacular architecture-employing a double-roof system of concrete slab and Calicá palm thatch, passive cooling strategies, and a minimal building footprint that sits lightly on the land. This article examines the construction principles behind such designs and how they apply to second-home development in temperate climates.
The Principles of Vernacular Architecture for Rural Second Homes
Vernacular architecture is a response to climate, available materials, labor skills, and cultural patterns of use. In temperate zones, generations of rural builders developed techniques that naturally moderated indoor conditions. Second homes, often unoccupied for extended periods, benefit from these passive strategies because they do not rely on active mechanical systems that might fail or waste energy during vacancy.
The House in Apulo follows the construction principles of the region using locally sourced materials and building forms that respond directly to site conditions. The house is a simple shed-like volume oriented to capture prevailing breezes. From a distance, the building reads as a palm-thatched shelter rather than a conventional suburban house transplanted into a rural setting.
Double-Roof Systems: Concrete Slabs and Natural Thatch
One of the defining features of this vernacular approach is the double-roof system. The House in Apulo has two distinct roof layers: a structural concrete slab that forms the ceiling of the interior rooms, and a second roof of wood framing covered with Calicá palm thatch suspended above it. This assembly addresses several construction challenges at once.
Structural and Climatic Logic of the Double Roof
The concrete slab performs as the primary weather barrier and structural diaphragm. It seals the interior from pests and rain infiltration while providing fire resistance above the thatch. The concrete also acts as thermal mass, absorbing heat during the day and releasing it slowly during cooler nights. Above the slab, the palm thatch roof extends well beyond the building walls, creating deep overhangs that shade the concrete and the walls beneath.
The ventilated air gap between the two roofs is the critical passive cooling mechanism. Hot air rising from the concrete slab escapes through gaps at the ridge of the thatch roof, drawing cooler air in through openings at the eaves. This natural chimney effect keeps the concrete slab cooler than it would be if exposed directly to the sun, and the interior spaces below remain comfortable without air conditioning.
Comparative Performance of Single vs. Double Roof Systems
| Performance Factor | Single Concrete Roof | Double Roof (Concrete + Thatch) |
|---|---|---|
| Solar heat gain through roof | High – direct sun on slab | Low – thatch shades slab |
| Ventilated air gap | None | Active convection draws heat away |
| Thermal mass benefit | Moderate – heats interior during day | High – mass stays shaded, cools at night |
| Rain noise attenuation | Loud | Thatch dampens sound |
| Wildfire resistance | High (concrete only) | Moderate – thatch is combustible, slab protects interior |
| Material carbon footprint | High (cement production) | Lower – thatch offsets some concrete impact |
| Visual landscape integration | Poor – reads as urban building | Excellent – reads as rural shelter |
The table above compares the two systems across performance factors relevant to rural second homes in temperate climates. Builders considering this approach should evaluate local fire codes and the availability of skilled thatch craftspeople before committing to the double-roof assembly.
Material Sourcing and Longevity
Calicá palm thatch, like many natural roofing materials, requires replacement every 8–12 years depending on exposure and rainfall. In the House in Apulo, the thatch is sourced from local palm species, supporting regional economies and reducing transport emissions. The concrete slab below ensures that the interior remains weathertight even as the thatch layer ages and develops gaps. This redundancy is a defining characteristic of well-designed vernacular buildings: no single system must perform perfectly because the layers work together.
Passive Cooling Strategies for Temperate Zone Retreats
Temperate climates in regions such as the Colombian highlands, the Mediterranean basin, and parts of the southern United States share a common pattern: warm days, cool nights, and wet and dry seasons. These conditions are ideally suited to passive cooling strategies without compressor-based refrigeration. The House in Apulo demonstrates three interlocking strategies that apply to second homes in similar climate zones.
Orientation and Cross-Ventilation
The building is oriented with its long axis perpendicular to the prevailing easterly breeze. Operable windows on both the windward and leeward sides create pressure-driven cross-ventilation. The selection of window types and their placement directly determines the effectiveness of natural ventilation. In the House in Apulo, high clerestory windows in the main living volume allow warm air to exit at the ceiling level while low operable casements on the shaded side draw in cooler air near the floor.
Key passive cooling tactics used in this project include:
- Deep roof overhangs (1.5–2.0 meters) that shade walls and windows during the hottest part of the day
- High thermal mass in the concrete slab floor and ceiling to absorb daytime heat gains
- Night-flush ventilation: windows left open overnight purge stored heat from the thermal mass
- Vegetation buffers: existing trees retained on the east and south sides block low-angle morning and afternoon sun
- Light-colored interior finishes that reflect rather than absorb radiant heat
Night Flush Cooling in Practice
The night flush cycle is the most effective passive cooling technique for temperate second homes. During the day, the concrete slab and walls absorb heat from occupants, appliances, and solar gain. After sunset, when outdoor temperatures drop below indoor temperatures, the building is opened to allow cooler outdoor air to flow across the thermal mass and extract the stored heat. By morning, the interior mass is cooled and ready to absorb heat again. The double roof enhances this cycle: the thatch layer keeps the concrete slab shaded during the day, and the ventilated air gap accelerates cooling at night.
Minimizing Landscape Impact Through Responsible Siting
Second homes in rural areas often cause unintended ecological damage: clearing native vegetation, altering drainage patterns, introducing invasive species, and fragmenting wildlife corridors. The House in Apulo addresses these concerns directly through siting decisions that prioritize the existing landscape over the building’s footprint.
The house is placed on a hilltop to minimize the need for earthmoving. No cut-and-fill grading was used; the structure adapts to the natural slope via a simple post-and-beam system that lifts the building off the ground. This approach has several benefits:
- Topsoil and existing root systems are preserved, preventing erosion
- Surface water drainage follows natural paths rather than being redirected by retaining walls
- Animals and insects can move freely beneath the building, maintaining habitat connectivity
- The building envelope stays above ground moisture, reducing long-term maintenance
Preserving Existing Vegetation as a Design Asset
Rather than clearing the building site, the architects surveyed every mature tree and integrated them into the design. Trees on the east and west sides provide crucial shading that reduces cooling loads. Native understory plants were retained around the foundation, eliminating the need for irrigation. The driveway is a simple gravel track with grass center strips, allowing rainwater to percolate rather than running off.
Material Selection and the Revival of Local Building Techniques
Vernacular construction depends on materials that are available within a reasonable radius of the building site. For the House in Apulo, the primary materials are concrete (locally mixed), Calicá palm thatch (harvested from managed groves within 50 kilometers), and regional hardwoods for framing and joinery. This material strategy carries direct benefits for both the project and the local economy.
Using local materials reduces embodied carbon from transportation. More importantly, it sustains the knowledge base of local craftspeople. Thatch roofing, stone masonry, and timber framing survive only when there is steady demand. Each vernacular second home built with local techniques provides work for artisans and material suppliers, keeping the tradition alive for the next generation.
An instructive parallel can be found in passive house design adapted for warm climates, where the same principles of thermal mass, shading, and natural ventilation apply using locally appropriate materials. The R-House project shows that the Passive House standard can be reinterpreted through a vernacular lens, using high-mass walls and deep overhangs instead of relying solely on mechanical ventilation with heat recovery. This cross-pollination between formal passive building standards and informal vernacular traditions produces resilient, low-energy buildings.
Balancing Modern Comfort with Vernacular Wisdom
Residents of second homes expect a baseline of comfort: reliable electricity, potable water, internet connectivity, and indoor temperatures that do not swing to extremes. The vernacular approach does not reject these expectations. Instead, it meets them using passive means as the first line of defense and reserves active systems for the periods when passive measures are insufficient.
In the House in Apulo, the concrete slab and palm thatch double roof keep indoor temperatures 5–8°C cooler than the outdoor peak on hot days. Ceiling fans provide air movement during still periods. A small, high-efficiency propane heater handles the rare cool nights. The house has no air conditioning. This is not a sacrifice; it is a design choice that eliminates the largest ongoing energy load from the building. The Everhart Passive House project demonstrates a parallel approach in a residential remodeling context, where careful envelope design and mechanical downsizing achieved dramatic energy reductions. The lesson applies to new second homes: invest in the envelope first, then size the mechanical system as small as possible.
For architects and builders considering a similar approach for clients in temperate regions, the following sequence of design decisions produces the best results:
- Select a site that uses existing topography and vegetation for passive shading and wind protection
- Orient the building to capture prevailing breezes for cross-ventilation
- Design a double-roof or well-ventilated attic assembly to separate the thermal mass from direct solar gain
- Specify locally sourced materials that support regional craft traditions
- Size glazing to optimize daylight without overheating – typically 20–30% of floor area on shaded orientations
- Install operable windows at both low and high levels to enable night-flush cooling
- Reserve mechanical cooling and heating for passive backup, not primary conditioning
Temperate-climate second homes that follow these principles become assets to their landscape rather than intrusions. They require less energy, need fewer repairs, and sit comfortably in their rural context. The House in Apulo, with its double roof of concrete and palm thatch, is a working model of how modern construction can return to the values of vernacular building-not as a nostalgic gesture, but as a practical response to climate, economy, and place.