The Passivhaus Standard

At Arbor, we believe in creating beautiful and sustainable living spaces to call home. Our approach to designing Passivhaus perfectly aligns with this and brings to life homes that are breathable, energy-efficient, and truly one-of-a-kind.

But what is Passivhaus?

By definition, “Passivhaus," or "passive house" in English, refers to structures built to energy-efficient design standards to maintain an almost constant temperature all year.

The Passivhaus standard represents the pinnacle of energy-efficient building design across the construction industry. These standards have been developed and championed by the Passivhaus Institute, who have fundamentally transformed the way we think about low-energy structures. The standard aims to create homes that maintain comfortable indoor temperatures year-round with minimal energy use. It embodies a whole-building approach that demands rigorous adherence to key performance metrics, ensuring comfort, health, and drastically lower energy bills.

The Passivhaus standard is based on building physics, with clearly measured targets focussed on user comfort, high-quality construction, healthy indoor environments and low energy bills.

Jalan Passivhaus

Key Features of Passivhaus:

• High Insulation Levels: Achieving U-values below 0.15 W/(m²K) for the building fabric​

• Airtight Construction: Limits air changes to less than 0.6 per hour at 50 Pascal, preventing unwanted draughts​ in new builds and 1.0 ACH for retrofit/EnerPHit

• Superior Glazing: Triple-glazed windows with Glazing U-values of 0.80 W/(m²K) or better​

• Mechanical Ventilation with Heat Recovery (MVHR): Guarantees a constant supply of fresh air while capturing a minimum of 75%, but most often 95% of heat from outgoing air​

• Thermal Bridge-Free Design: Minimises energy loss at structural junctions. These meticulous measures result in buildings that use up to 90% less energy for heating and cooling compared to conventional buildings.

Passivhaus in Practice

Our work is guided by a “fabric-first” philosophy, emphasising high-performance materials and detailing to create airtight, well-insulated buildings. in designing homes that harmonise aesthetics, sustainability, and cutting-edge building science.

Our designs also consider the long-term benefits that Passivhaus offers. According to Passivhaus Trust, these include not only reduced energy demand but also enhanced indoor air quality, consistent comfort, and resilience to climate extremes​.

Passivhaus has evolved over the years to include various levels of certification that cater to different building types, energy needs, and sustainability goals.

1. Classic Passivhaus

This is the traditional standard that most people associate with Passivhaus. It sets the bar for exceptional energy efficiency while ensuring comfortable indoor environments. The key requirements for Passivhaus Classic include:

• Heating Demand: Less than 15 kWh/m²/year or a peak heating load of 10 W/m².

• Primary Energy Demand: Total energy consumption for heating, cooling, hot water, and household electricity must be less than 135 kWh/m²/year.

• Airtightness: Air leakage must not exceed 0.6 air changes per hour at 50 Pascals.

• Thermal Comfort: Internal surface temperatures must remain above 17°C year-round​.

Fishley Passivhaus is one of our certified Passivhaus projects.

Bicester Eco Business Centre - Jack Hobhouse

2. Passivhaus Plus

Passivhaus Plus builds on the Classic standard by integrating renewable energy generation. This level is ideal for those seeking to not only reduce energy consumption but also contribute to renewable energy production. The main criteria include:

• Heating and Airtightness: Same as the Classic standard.

• Primary Energy Renewable (PER) Demand: Limited to 45 kWh/m²/year, ensuring that the energy consumed is more than offset by renewable energy generated on-site.

• Renewable Energy Contribution: The building must produce enough renewable energy to offset a significant portion of its energy use.

Passivhaus Plus supports a balance between energy efficiency and sustainable energy generation, making it an excellent choice for projects that aim for a low-carbon footprint.

Bicester Eco Business Centre achieved Passivhaus Plus in 2021.

3. Passivhaus Premium

The Premium level is designed for buildings that push the boundaries of sustainability by generating more energy than they consume. This level is suited for those aiming for a net-positive energy building. The criteria for Premium include:

• Heating and Airtightness: Same as Classic.

• PER Demand: Reduced to 30 kWh/m²/year, which is even stricter than Passivhaus Plus.

• Higher Renewable Energy Production: The building must generate a significant surplus of energy, well beyond its own needs.

Passivhaus Premium is ideal for ambitious projects where energy independence and environmental leadership are primary goals.

4. PHI Low Energy Building Standard

This is a newer energy-efficiency certification by the Passivhaus Institute (PHI) that offers a more accessible route to sustainable building compared to the classic Passivhaus levels. While it doesn’t reach all the same stringent performance metrics as Passivhaus Classic, it is an excellent entry point for projects aiming for substantial energy reductions without meeting full Passivhaus criteria. The standard requires:

• Heating Demand: Must be less than 30 kWh/m²/year. This is more lenient than the Passivhaus Classic requirement of 15 kWh/m²/year.

• Primary Energy Demand: Must not exceed 150 kWh/m²/year, providing a flexible threshold that still supports significant energy savings compared to conventional buildings.

• Airtightness: The standard still prioritises good airtightness but allows for slightly higher air change rates than the 0.6 ACH @ 50 Pa required for Passivhaus. Typically, this is capped at around 1.0 ACH @ 50 Pa.

Take a look at our PHI Low Energy project, Hawksfield House

What is EnerPHit?

EnerPHit is the Passivhaus Institute’s retrofit standard, designed for upgrading existing buildings. While new construction can be optimised for energy performance from the ground up, retrofits must overcome unique challenges such as structural constraints. EnerPHit adapts Passivhaus principles to existing buildings, enabling deep energy cuts and better indoor environments.

Core Benefits of EnerPHit:

• Improved Energy Efficiency: Reduces energy demand significantly, mitigating rising fuel costs​

• Enhanced Comfort and Health: Ensures consistent temperatures and superior ventilation​

• Climate Resilience: Prepares homes for future extremes with thermal stability​

Our recently completed Tin Barn project has achieved the EnerPHit standard and has demonstrated that even derelict buildings can be transformed into highly energy efficient homes.

Along with the understanding of building physics that creates low energy architecture, we never take our ‘Architect / Designer’ hats off. Our work is underpinned by the ethos that delivering well-crafted, timeless and enriching spaces is only possible if the architecture is rooted in its context and designed in collaboration with the people who will inhabit and interact with it. We believe our approach to Passivhaus and EnerPHit perfectly aligns and creates spaces that are seamlessly energy-efficient, healthy and environmentally responsive.

Interested in learning how Passivhaus or EnerPHit could transform your project? Contact us to see how we can help bring your vision of a sustainable home to life.