Bio-based homes in England: Llama Croft – Proof that better building is possible, even in a moist climate

Seb Laan Lomas and his wife, Janna, met while studying architecture and environmental studies in Wales. Seb built a career in sustainability, now working at Architype Architects on Building Performance Evaluation and climate action. Janna, passionate about natural materials, founded Grain Architecture and designed their family home - Llama Croft, inspired by French farmhouse elegance, reflecting her vision entirely, with Seb's sole contribution being a commitment to achieving Passivhaus Certification, now a staple consideration in her practice.

The design of Llama Croft balances modesty with well-proportioned, material-rich interiors. They’ve aimed for sustainability in each choice: the home is concrete-free, elevated on screw piles, and avoids plastic unless absolutely unavoidable. As an homage to bio-based materials, they are using clay plaster from their garden on light-earth walls, made of straw and clay, providing thermal mass and sound insulation.

The house’s breathable structure promotes indoor air quality and material health, beginning with lime render on woodfibre insulation and incorporating warmcel / cellulose (recycled newspaper) in a deep timber Larsen-truss frame. An OSB layer with airtight coating, a service cavity, and clay-plastered, homemade lath complete the exterior walls.

Architype has long advocated for structural timber due to its sustainability, but recent high-profile failures, such as a £100m insurance claim for moisture-damaged CLT, have intensified scrutiny of its use. The Laan Lomas family’s dream home, Llama Croft, provided a chance to explore best practices for ensuring timber resilience in challenging environments.

While Seb expected no issues with their project, it became an opportunity to leverage Tector’s system as both a learning experience and a showcase of the value of advanced moisture monitoring. Architype aims to reassure clients and insurers that timber structures can thrive even in damp climates like England’s. As a firm committed to starting with structural timber wherever feasible, Architype sees proactive monitoring as essential to addressing industry concerns around moisture risks.

“Architype have used several technologies in the past to measure moisture but the exciting USP of Tector was that the data is live streamed to the cloud, making it a much more instantaneous feedback loop - critical when relying on it for informing any reactive interventions.”

Ten Tector sensors were installed at key points of Llama Croft’s structure, including:

• The north and south facades to monitor how moisture levels fluctuated across varying exposures.
• Within the vapour-open wall system, with sensors at the outer and inner timber studs to track moisture movement through the lime render, woodfibre insulation, and clay plasters.

When the lime render was applied to the walls at Llama Croft, the sensors captured a fascinating insight. Within 48 hours, the moisture content in the outer timber stud rose by 12% as the render released moisture inward. Just 16 hours later, this moisture began desorbing outward, while the inner timber stud remained completely unaffected throughout. This demonstrated the vapour-open wall system working exactly as intended—a clear confirmation of the design’s effectiveness.

During construction, the same wall faced a significant challenge when heavy rain saturated the timber studs, spiking moisture levels to 60%. Thanks to the vapour-open wall design, the sensors recorded a steady drying process, with the timbers returning to a safe moisture level. This real-time data not only validated the design but also provided reassurance that the structure remained uncompromised despite challenging conditions.

Another key moment came when Warmcel insulation was installed in the external walls. Before insulation, the sensors recorded inconsistent temperature and humidity fluctuations. Once the walls were fully insulated, these readings smoothed out, reflecting a stable and controlled internal environment. Even before the doors were installed, the walls began buffering external temperature impacts—a testament to the home’s high-performance Passivhaus design.

These observations, captured in real time by Tector’s monitoring system, showcase the benefits of using advanced moisture detection for bio-based materials. From validating design principles to ensuring the long-term health of the structure, Llama Croft demonstrates how technology and sustainability work hand in hand.

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Tector’s system provided crucial data that validated the effectiveness of Llama Croft’s vapour-open design. Key results included:

• Confidence in the design: Real-time monitoring confirmed that the timber remained within safe moisture levels throughout construction, even after exposure to rain and lime render.
• Proof for insurers: The data demonstrated that the design mitigated risks effectively, offering a compelling case for lower insurance premiums for timber structures.
• Educational value: Architype gained valuable insights to apply in future timber projects, empowering them to advocate for timber as a sustainable alternative to high-carbon materials.

As Seb Laan Lomas explained, “My hope is that by deploying technologies like Tector’s, we can see more and more buildings built from structural timber, proving it’s not only sustainable but resilient—even in challenging climates.”

Llama Croft stands as a testament to what’s possible with bio-based construction, proving that doing better is achievable—even in England, where it’s pretty much moist all the time.