Our Approach to Passivhaus: Key Elements of a High-Performance Build

When envisioning a new building or renovation, there's often a central dilemma, how to create a design that is both beautiful and highly efficient?

The desire for contemporary aesthetics, sleek lines and expansive glass, can often feel at odds with an often pre-requisite for thick monolithic walls associated with high-performance buildings like Passivhaus.

The reality is, achieving both stunning design and exceptional energy efficiency requires a deeper, more technical understanding of materials and systems, integrated from a project's earliest stages.

At OSOTIMBER, we believe you shouldn't have to compromise.

Our expertise in timber frame construction, combined with a collaborative approach, allows us to deliver high-performance Passivhaus and modern sustainable buildings that meet the most stringent energy standards, whilst still realising your boldest design visions.

In this blog series, we'll delve into the technical solutions that make this possible, from foundations and framing solutions to fabric and insulation choices all of which contribute to the end performance, aesthetic and experienced feeling a building provides throughout its lifecycle, demonstrating how early collaboration is the key to unlocking true building potential.

Approx. 5 min read

PART 1

The Foundation: Recycled Foam Glass. A Multi-Purpose, All-in-One Solution

Traditional foundations, whether conventional concrete strip or raft systems, often represent a significant weak point in a building's thermal envelope and moisture management strategy.

The reliance on moisture-impermeable polythene membranes (Damp Proof Membranes) can, over time, lead to serious issues. As water pressure builds up beneath the slab, moisture can move sideways and rise within the existing masonry, often exacerbated by waterproof renders which trap it. Similarly, poly-based systems and Swedish rafts are closed-pore, forcing reliance on drainage systems like French drains, which can be prone to blockages and future damage.

At OSOTIMBER, we advocate for solutions that tick multiple boxes, and our foundation system of choice is a perfect example.

While we champion bio-based solutions because they so often serve multiple purposes, we also appreciate how certain non-bio materials can deliver similarly holistic benefits. That's why we choose to use recycled foam glass (RFG) on minimal strip foundations. This approach allows for minimal use of concrete or, for a completely cement-free solution, the use of hydraulic lime in place of concrete strip foundations is a viable and proven alternative.

Geocell LABC registered detail example - one of many details that can be designed and configured best to suit the application - from swimming pools to new build homes, this product ticks a lot of boxes!

Benefits of Recycled Foam Glass Foundations

RFG is a truly unique material that performs a remarkable number of roles in a single, elegant step. Made from 100% recycled glass, this cellular aggregate forms a continuous, insulating sub-base beneath the concrete slab, creating a "warm raft" that is far more advanced than conventional methods.

The benefits of RFG are unparalleled:

• Insulation: The material consists of millions of closed cells, and the air trapped inside is responsible for its outstanding insulating properties. With a thermal resistance capability of 0.080 W/mK, RFG virtually eliminates thermal bridging at the ground floor level, ensuring a consistent, high-performance thermal envelope.

• Fire Resistant: Recycled foam glass is classified as A1 fire-resistant. This is the highest possible rating for a building material, meaning it is completely non-combustible and will not contribute to the spread of fire, offering an enhanced layer of safety to the foundation system.

• Anti-Capillary Action: With its closed-cell structure, RFG is a natural capillary break. It prevents moisture from being "sucked up" into the building fabric, while allowing water to drain safely beneath the foundation system. This not only keeps moisture away from the walls, preventing mould growth and structural damage, but also removes the need for a separate Damp Proof Membrane.

• Superior Drainage: RFG's structure means that rainwater is immediately drained away from the building. Unlike systems that rely heavily on separate and well functioning drainage solutions, this approach effectively manages water whilst also offering the additional benefit of insulating the outside of existing walls.

• Lightweight & Load Bearing: With a dry bulk density of approximately 150 kg/m3, RFG is extremely lightweight, making transport and installation quick and easy. Yet, thanks to its glass cell structure, it provides excellent compressive strength, rated at 275 KN/m2 (27.5tonne/m2) at a compaction factor of 1.3:1, easily supporting the building's loads.

• Freeze-Thaw Resistance: RFG does not react to the freeze-thaw cycle, effectively protecting against the impact of frost. No additional frost protection is required.

Our good friend Nigel Gervis @ Ty-Mawr Lime Ltd gives a nice demonstrative example of the build up and benefits of using RFG in a foundation system.

Beyond the practical advantages, the choice of RFG for your foundation is a powerful statement about sustainability.

This material is made from 100% post-consumer waste glass, sourced from recycling centres and bottle banks to give a new life to materials that would otherwise be discarded.

We believe this product represents a truly viable lower embodied carbon alternative to the norm, whilst relying on zero virgin raw materials. It's an inert, non-toxic, PH-neutral product that can be re-used and recycled, making it a great circular solution for your project.

By integrating RFG foundations, we ensure your building's thermal performance starts strong from the ground up, contributing significantly to its overall energy efficiency and long-term health.

We’ve laid the foundation, both literally and figuratively. In the next part of this blog series, we’ll tackle the very heart of the building: the frame. We’ll show you how we overcome the challenge of balancing structural integrity and performance with the aesthetic vision you’ve worked so hard to create.

Written by Natalie Ross