Passivhaus has become the benchmark for energy efficiency in residential construction, setting rigorous standards not only for thermal performance and airtightness but also for passive design principles that optimise comfort and reduce reliance on mechanical heating and cooling. Originating in Germany, the approach prioritises maximising natural heat gains, whilst minimising heat loss. Achieving these standards requires careful consideration of insulation, airtightness, and thermal bridging, alongside the integration of mechanical ventilation with heat recovery. Traditional housebuilding methods often require multiple layers of additional insulation and complex detailing to meet these requirements. However, one construction method, Insulating Concrete Formwork (ICF), naturally lends itself to the Passivhaus approach. With its continuous insulation, high thermal mass, thermal-bridge free and airtight structure, ICF provides a practical and highly effective solution for creating homes that meet and exceed Passivhaus standards.
The Part L regulations represent the legal minimum energy performance standards for new dwellings in England, focusing on reasonable measures to conserve fuel and power in line with national carbon reduction targets. They aim to improve insulation, reduce air leakage, and encourage the use of efficient heating systems, but still allow for flexibility in design and construction methods.
Passivhaus, by contrast, is a voluntary certification standard that takes energy efficiency much further. It promotes a fabric-first approach that prioritises extremely high levels of insulation, airtightness, and passive solar design to reduce heating demand to a minimum. Rather than setting minimum requirements, Passivhaus demands holistic building performance across all aspects of the envelope and services, ensuring long-term comfort and energy savings. While Part L focuses on improving new-build homes at a national scale, Passivhaus sets a benchmark for ultra-low energy performance that consistently exceeds regulatory compliance.
| Element | Part L Regulation | Passivhaus Standard (Classic) |
|---|---|---|
| Wall U-value | 0.18 W/m²·K | 0.15 W/m²·K |
| Roof U-value | 0.11 W/m²·K | 0.10 W/m²·K |
| Floor U-value | 0.13 W/m²·K | 0.10–0.15 W/m²·K |
| Window U-value (whole window) | 1.2 W/m²·K | 0.80 W/m²·K (triple-glazed, typically with g-value ~0.5) |
| Door U-value | 1.0 W/m²·K | 0.80–1.00 W/m²·K |
| Airtightness | 5.0 m³/h·m² @ 50 Pa | 0.6 ACH @ 50 Pa (approximately 0.6 m³/h·m² or better) |
| Thermal bridging | Accredited details or psi-values modelled | Thermal bridge-free design required (ψ-values ~0 W/m·K) |
| Primary Energy Use (PE) | SAP-derived target (varies by system, ~50–100 kWh/m²/yr) | 120 kWh/m²/year (delivered energy, all uses) |
| Space Heating Demand | No specific limit (performance is averaged across dwelling) | 15 kWh/m²/year or ≤ 10 W/m² peak load |
| Ventilation (MVHR optional) | Natural or mechanical systems allowed, must meet Part F | Mechanical Ventilation with Heat Recovery (MVHR) required |
| Overheating | Part O requires limiting solar gains/overheating | Internal temperatures must stay below 25°C for 10% of year max |
In the UK, the Passivhaus standard is supported by a number of regulatory bodies and organisations that ensure compliance with energy efficiency and sustainability requirements. The Passivhaus Trust is the primary UK-based authority, promoting the Passivhaus standard and working to increase its adoption across the residential and commercial sectors. They offer support and guidance on design, certification, and training, ensuring that buildings meet the rigorous energy efficiency targets set by the standard.
Additionally, the UK Green Building Council (UKGBC) and Building Research Establishment (BRE) play significant roles in advocating for sustainable building practices and integrating Passivhaus principles into mainstream construction. While Passivhaus is not a mandatory requirement under UK building regulations, it aligns closely with the country’s push towards net zero carbon homes and is increasingly being used as a benchmark for energy-efficient residential and commercial buildings. The UK government’s Part L (Conservation of Fuel and Power) regulations also support many of the principles of Passivhaus, particularly in terms of airtightness, insulation, and overall building performance, guiding builders and developers towards more sustainable construction methods. Unfortunately, these regulations fall short of the Passivhaus standards.
Heating Requirements:
Part L vs Passivhaus
| Building Standard | Heating Requirements kWh/m2/Year | Reduction |
|---|---|---|
| Part L | 63 | 0 |
| Passivhaus Classic | 15 | 76% |
One fundamental principle of Passivhaus design is to create a highly efficient building envelope that prevents heat loss, eliminates draughts, and maintains a stable internal temperature. This is achieved through exceptionally low U-values, advanced insulation techniques, and meticulous attention to air leakage and ventilation. A home built to Passivhaus standards will typically use up to 90% less energy for heating compared to a traditional new build, delivering not only environmental benefits but significant cost savings for homeowners. However, reaching this level of efficiency with conventional materials can be complex and expensive, requiring multiple layers of insulation, specialist airtight membranes, and continuous quality control throughout construction.
ICF simplifies this process by offering a construction method that inherently delivers high levels of insulation and airtightness without the need for additional materials or complex installation techniques. ICF blocks consist of two layers of EPS insulation, which act as both the permanent formwork for the concrete and the insulation of the house, solidified with a reinforced concrete core, cast in between. This creates a highly insulated, airtight structure that naturally meets many of the key requirements of Passivhaus design.
One of the greatest challenges in achieving Passivhaus certification is reducing heat loss through the external walls, floors and roof. ICF offers exceptional thermal performance, with U-values as low as 0.10 W/m²K, well below standard building regulations, and exceeding the current Passivhaus standard of 0.15 W/m²K in the walls. The continuous insulation provided by ICF eliminates weak points where heat can escape, significantly improving energy efficiency without requiring multiple additional layers of insulation. Unlike traditional masonry, which often relies on cavity wall insulation or external cladding, ICF provides a complete, highly insulated shell from the outset, ensuring a consistent level of thermal performance throughout the structure.
Airtightness is another critical factor in Passivhaus design, requiring homes to achieve an air leakage rate of less than 0.6 air changes per hour. Traditional construction methods often require additional sealing, tapes, and membranes to meet this standard, but ICF naturally provides an airtight structure due to its solid concrete core, cast in-situ. The absence of joints and gaps in the external walls significantly reduces the risk of air leakage, ensuring a more stable indoor environment with minimal heat loss. Example airtightness test have showcased results of 0.26 air changes per hour!
Thermal bridging, where heat escapes through gaps or poorly insulated junctions, is a common problem in many homes and can have a significant impact on energy efficiency. ICF virtually eliminates thermal bridging by providing continuous insulation across the entire building envelope. Unlike traditional construction, where junctions between floors, walls, roofs, windows, and doors often create weak points, ICF ensures that insulation remains unbroken, even at critical junctions. This not only improves overall thermal performance but also reduces the risk of condensation and cold spots, which can lead to damp and mould issues in poorly insulated homes.
Beyond its energy efficiency benefits, ICF also provides a more comfortable and stable indoor environment. The concrete core acts as a thermal mass, absorbing and storing heat during the day and releasing it gradually when temperatures drop. This prevents overheating in summer and helps maintain warmth in winter, reducing temperature fluctuations and ensuring a consistent indoor climate throughout the year. The result is a home that is not only highly energy efficient but also more comfortable to live in.
Building a Passivhaus home requires precision and attention to detail, particularly when it comes to ensuring airtightness and insulation continuity. The simplicity of ICF construction makes it easier to achieve these high standards without the need for specialist materials or labour-intensive processes. The blocks are quick to assemble, significantly reducing construction time compared to traditional methods, and the integrated insulation means that additional layers of insulation and airtight membranes are not required. This not only speeds up the building process but also reduces material waste, making ICF an environmentally friendly choice for sustainable construction.
Many real-world projects have demonstrated the effectiveness of ICF in achieving Passivhaus standards. Homes built using ICF have consistently achieved air leakage results well below the required Passivhaus threshold, with some tests showing airtightness levels as low as 0.26m³/(h.m²), proving that with careful detailing, these targets are well within reach. In addition, homes constructed using ICF have been shown to exceed UK building regulations by over 50%, dramatically reducing heating demand and running costs.
For developers, architects, and self-builders looking to create homes that meet Passivhaus standards, ICF provides a practical and effective solution. It simplifies the construction process, reduces the risk of air leakage and thermal bridging, and delivers outstanding thermal performance without the need for complex additional measures. The result is a home that is not only built to the highest energy efficiency standards but is also durable, cost-effective, and comfortable to live in.
At ICF Bondmor, we recognise that not every project is built to full Passivhaus standards, but we believe in pushing the boundaries of what is possible. Our construction approach consistently delivers airtight, highly insulated, and energy-efficient homes that exceed standard building regulations, and when Passivhaus is the goal, we achieve it with ease. More importantly, we are demonstrating to the wider development industry that these standards are not just achievable but scalable. Passivhaus is often perceived as expensive and complex, yet with ICF, it becomes a commercially viable and cost-effective solution. By integrating these principles into our work, we are not only improving the sustainability of individual homes but also driving change in the industry, showing that low-energy, high-performance housing can be both practical and profitable at scale.