IB House

Aitor Estevez

• Architects

Applied products

Alo Ondarreta

BAT Bilbao Architecture Team completes a 910 m² two-family house built in cross-laminated timber (CLT) and clad in a distinctive charred larch façade crafted using the Japanese Shou Sugi Ban / Yakisugi technique. Conceived under principles of sustainability, energy efficiency and low environmental impact, the two dwellings propose a new way of inhabiting the landscape through a unique spatial experience in which geometry and light become the true protagonists. The project reinterprets the local timber building tradition through a contemporary, precise and sustainable approach.

photo_credit Aitor Estevez — Aitor Estevez

The building is organised into two L shaped volumes that define both the exterior spaces and the internal layout, giving each dwelling its own distinct character. Two strong linear gestures cut through the main volume, generating spaces that establish unique relationships between the different rooms. The dwellings are structured around these axes, creating voids of double and triple height that mark the entrance and the main social space of each home. These fissures allow natural light to shape the interior life, visually connect the different levels and extend the houses outward, blurring the boundaries between architecture and the surrounding landscape. Both houses come together as a single architectural entity, linked by a shared structural strategy yet distinguished by their own identity and character.

The cross laminated timber structure not only supports the building but remains exposed throughout much of the project, expressing itself with clarity and honesty, visible both inside and outside. Within the interior it takes on a leading role, particularly in the vertical circulation areas such as the staircases, where it acts as the backbone of the project and reinforces continuity between levels.

In its natural, continuous grain, the timber brings warmth to the spaces through ceilings, walls and stairs. Overhead light softens the surfaces, modulating the visual temperature of the space. Neutral tones and refined materials complete a serene and contemporary atmosphere, consistent with the exterior architecture.

The ensemble is fragmented into four pitched roof volumes surrounding a central flat roof body. This composition creates a dynamic interplay of heights and rhythms, giving movement to the volumetry and reinforcing its relationship with the topography.

The interiors unfold over three levels, visually and spatially connected by vertical bands of double height spaces that flood the living areas and staircases with natural light, while large façade openings illuminate the bedrooms and kitchens. The main floors accommodate the entrance and social areas, including the kitchen and living dining space, with generous windows opening onto the outdoor pool area and integrating domestic life with the surrounding landscape.

On the upper level, the private areas such as bedrooms and bathrooms form a more intimate and sheltered environment. The lower level houses the garages and gathering spaces, illuminated by glazed English courtyards that bring natural light into the lower floor and enhance comfort. Continuity between exterior and interior is reinforced through the presence of timber, which acts as the true thread running throughout the project.

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Sustainability and Material Innovation: CLT Construction and the Yakisugi Technique

Around 50 percent of global CO₂ emissions come from the construction sector, making low environmental impact design an unavoidable responsibility. In this context, BAT Bilbao Architecture Team adopts two construction systems in this project that combine technical innovation and craft tradition: cross laminated timber (CLT) and a charred larch façade treated using the Japanese Yakisugi (焼杉), also known as Shou Sugi Ban.

The use of CLT allows for a renewable and recyclable material that stores CO₂, reduces environmental impact and improves the building’s thermal performance. Its industrialised process enables faster, more precise and flexible construction while minimising waste and resource consumption. In addition, its high structural strength and insulating capacity contribute to comfort and energy efficiency. The Shou Sugi Ban or Yakisugi technique, a centuries old process, not only enhances the appearance of the timber but also provides natural protection against moisture, fire, insects and weathering. The controlled charring of the wood surface extends the lifespan of the material without the need for chemicals and gives the timber a deep texture and dark tone that reinforce the building’s contemporary identity.

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All these qualities, together with the promotion of certified and responsibly sourced timber, make it an ideal choice for buildings seeking longevity and environmental responsibility. Both strategies reflect an architectural vision committed to sustainability, where innovation and natural materials come together to create architecture that is more durable, responsible and emotionally resonant.

The completion of this two-family house follows another project finalised at the end of 2025 with a fully cross laminated timber structure: IES Muskiz, one of the most significant educational buildings in terms of sustainability in the Basque Country and Spain. Both projects demonstrate how constructive innovation and the responsible use of timber can be successfully integrated into residential architecture as well as public educational buildings.