Swiss architect Olin Petzold has designed a self-built treehouse named Casetta Tessino that nestles within the Onsernone Valley in Switzerland's Locarno district. The triangular structure serves as a woodland writing studio for a Swiss artist and climate activist who sought refuge in nature. Constructed from light materials including larch wood beams and polycarbonate panels, the treehouse rises above the forest floor, supported by three oak trees. This innovative project demonstrates how architectural design can respond to both environmental constraints and the human desire for connection with nature. The 150-meter distance from the client's main house provides separation while maintaining practical accessibility for daily use.

Local building regulations prevented traditional foundation work or house extension, prompting the creative solution of an elevated treehouse. The client, an artist and climate activist, had long dreamed of sleeping surrounded by forest wildlife and vegetation. Petzold drew inspiration from American naturalist Henry David Thoreau's book Walden, which chronicles simple living in natural surroundings. This philosophical foundation shaped the project's emphasis on minimal environmental impact and self-sufficiency. The design prioritizes lightness, both physically and visually, to minimize its footprint on the sensitive woodland ecosystem while maximizing the sensory experience of forest living.

The structural system centers on three larch wood beams fixed around three oak trees, creating a suspended triangular base. A ladder provides access to this elevated platform, where a spruce shelter with an equilateral triangle plan sits at a rotated angle. Polycarbonate panels clad the exterior, offering translucent protection while maintaining visual connection to the surrounding forest. Petzold deliberately selected materials that could be handled without heavy machinery, enabling the client to execute the entire project as a self-build. This approach democratizes construction and strengthens the personal relationship between inhabitant and structure, making the building process part of the overall experience.

Inside, a long wooden plank spans one wall to form a bench, while another plank creates a desk for writing and contemplation. A bed hides beneath the floor, revealed by removing four wooden planks, maximizing the compact interior's functionality. The triangular shape defines distinct zones for sleeping, sitting, and writing within minimal square footage. Petzold's detailing ensures that untrained workers can assemble the components, making sophisticated design accessible to non-professionals. This interior efficiency reflects the treehouse's overall ethos of simplicity and purposeful living, where every element serves multiple functions.

The polycarbonate panels respond intelligently to the forest's seasonal climate dynamics. During summer, the dense tree canopy provides natural shading, preventing overheating. In autumn and winter, when leaves fall, sunlight penetrates the translucent panels to warm the interior naturally. Bottom-hinged windows on each facade open for ventilation, creating passive cooling when needed. This bioclimatic design approach eliminates mechanical systems, reducing both environmental impact and maintenance requirements. The treehouse thus operates in harmony with its natural context rather than fighting against it, exemplifying sustainable design principles.

Casetta Tessino exemplifies a growing trend toward small-scale, sustainable architecture that prioritizes environmental integration over domination. By empowering the client to self-build, Petzold created not just a structure but an intimate understanding of sustainable living. The project demonstrates that architectural sophistication need not depend on complex construction techniques or expensive materials. For the client, the treehouse fulfills multiple roles: guest accommodation, writing retreat, and personal sanctuary. As climate consciousness grows, such projects offer models for living lightly on the land while maintaining deep connection to place and community.