Fabric First: Designing for Performance with Passivhaus Principles

Featuring our Cambridgeshire Eco Bungalow as a Case Study 

In the pursuit of sustainable, low-energy buildings, the principle of Fabric First has become a cornerstone of effective design strategy. Rather than relying on bolt-on technologies or post-occupancy adjustments, a Fabric First approach prioritises the performance of the building envelope itself — ensuring that the structure is inherently efficient, comfortable, and durable from day one.

At Eco Design Consultants, our commitment to Fabric First principles is embedded in every project we undertake. A recent example is our Cambridgeshire Eco Bungalow — a single-storey, replacement dwelling in South Cambridgeshire designed and built to full Passivhaus standards (though the client did not want to presure certification). This project exemplifies how carefully considered fabric design can deliver both comfort and sustainability without compromise.

What is the Fabric First Approach?

The Fabric First methodology focuses on maximising the performance of a building’s elements — such as walls, roofs, floors, windows, and airtightness — to minimise energy demand before considering mechanical or renewable technologies. This includes:

  • High levels of insulation to reduce heat loss through the building envelope

  • Exceptional airtightness to prevent unwanted draughts and heat leakage

  • Optimised glazing and solar gain to reduce winter heating loads

  • Thermal bridge-free detailing to eliminate weak points in the fabric

  • Mechanical ventilation with heat recovery (MVHR) to maintain indoor air quality efficiently

By getting the fabric right, the building can maintain a stable internal environment with minimal energy input, offering long-term benefits in comfort, energy bills, and carbon emissions.

Passivhaus: A Rigorous Fabric First Standard

The Passivhaus Standard (or Passive House) is one of the most stringent, science-based frameworks for delivering Fabric First buildings. It sets clear performance targets, including:

  • Annual heating demand of ≤ 15 kWh/m²

  • Primary energy demand of ≤ 60 kWh/m²

  • Airtightness of ≤ 0.6 air changes per hour @50Pa (ACH)

  • Thermal bridge-free construction throughout

Passivhaus requires rigorous modelling using the PHPP (Passivhaus Planning Package), combined with site testing and quality assurance to confirm that performance targets are achieved in practice — not just on paper.

Case Studey: Cambridgeshire Eco Bungalow

Our recently completed Cambridgeshire Eco Bungalow provides a practical illustration of Fabric First and Passivhaus design in action.

The client approached us with a brief to replace an ageing bungalow and garage with a new, energy-efficient ‘forever home’ that would combine traditional character with exceptional performance. Located on the edge of the green belt and opposite a Grade II listed building, the project required careful architectural sensitivity and robust planning documentation — including a heritage statement and biodiversity report.

Despite its traditional appearance, the building is anything but conventional in its performance:

  • The design was fully modelled in PHPP and met all key Passivhaus performance criteria

  • The airtightness testing returned results within the required threshold for certification

  • A hipped roof form reduced massing and ensured a consistent visual profile

  • High-performance glazing and optimised orientation allow generous daylight and countryside views while avoiding overheating

  • The building is fitted with an MVHR system, ensuring excellent indoor air quality with minimal heat loss

While the client ultimately chose not to pursue formal Passivhaus certification, the project stands as a testament to what can be achieved through a meticulous Fabric First approach. It demonstrates that high-performance eco homes need not sacrifice visual appeal or planning sensitivity — nor rely on complex technologies to deliver comfort and efficiency.

Why Fabric First Matters

There are compelling reasons to adopt Fabric First as the foundation of sustainable design:

  • Longevity: Fabric improvements last the lifetime of the building; technologies may require replacement in 10–15 years

  • Cost-effectiveness: Reducing energy demand at source lowers the need for expensive renewable systems

  • Comfort and health: Stable internal temperatures, good air quality, and lack of draughts significantly improve occupant wellbeing

  • Carbon reduction: Fabric efficiency cuts operational emissions and contributes to net-zero goals

Fabric First also supports a more resilient, future-proof housing stock — especially as energy prices fluctuate and climate change drives more extreme weather patterns.

Conclusion

As our Cambridgeshire Eco Bungalow project illustrates, designing a sustainable home starts with the fabric. By aligning early-stage design with Passivhaus principles — even when certification is not pursued — we can deliver low-energy homes that are not only environmentally responsible but also beautiful, durable, and enjoyable to live in.

At Eco Design Consultants, we continue to champion Fabric First as the most effective route to long-term sustainability in architecture. If you’re considering an energy-efficient new build or renovation, we would be delighted to help guide your project from concept to completion.

Explore the full Cambridgshire Eco Bungalow project here

South-facing view of Passivhaus-standard eco home with large windows and level decked terrace overlooking countryside.
Fabric First in action – detail of airtightness strategy during construction.
Bright, open-plan interior of low-energy home with high levels of insulation and MVHR system for comfort and air quality - kitchen.
Layered for performance – a Passivhaus approach to envelope design