As energy efficiency becomes an increasingly important factor in home renovations, many homeowners are looking for ways to improve the performance of their existing properties.
This is where EnerPHit, the gold standard for retrofitting, comes into play. Designed by the Passivhaus Institute, EnerPHit offers a rigorous framework for upgrading existing buildings to near-Passivhaus levels of energy efficiency.
In this guide, we’ll explore what EnerPHit entails, its key requirements, the benefits it provides, and whether it’s the right fit for your home retrofit project.
While Passivhaus standards set the benchmark for new builds, EnerPHit has been specifically developed for existing properties undergoing retrofit projects. Retrofitting is the process of renovating a building to significantly improve its thermal performance, energy efficiency, and indoor comfort while reducing energy consumption. Unlike new-build Passivhaus projects, which allow for complete design freedom from the outset, retrofit projects must contend with pre-existing structural conditions, orientations, and thermal bridges (cold spots where heat escapes more easily).
Recognising these constraints, EnerPHit sets slightly more achievable performance targets than Passivhaus. The key differences include:
Energy Demand: Passivhaus requires space heating and cooling demand to remain below 15 kWh/m²/year, while EnerPHit allows up to 25 kWh/m²/year, reflecting the inherent limitations of retrofitting.
Airtightness: The airtightness standard for Passivhaus is 0.6 air changes per hour (ACH), while EnerPHit permits 1.0 ACH, still far superior to most existing homes, where air leakage can be 5-15 ACH.
Despite these differences, achieving EnerPHit status means dramatically improving your home’s energy performance compared to standard renovations, offering long-term cost savings, comfort, and reduced environmental impact.
EnerPHit provides a structured approach for achieving a highly energy-efficient retrofit. Like Passivhaus, it relies on the Passivhaus Planning Package (PHPP), a design tool that helps architects and engineers model energy performance. This allows design teams to make informed decisions about insulation, ventilation, and other key elements from the early stages of the project.
However, retrofitting is rarely straightforward. The constraints of working with existing structures mean that achieving EnerPHit requires careful planning, particularly regarding:
Insulation Strategies: Deciding between internal or external insulation is crucial, as each has different impacts on thermal performance and moisture management.
Airtightness Challenges: Retrofitting airtightness measures is often more complex than in a new build due to pre-existing gaps and construction details.
Moisture Risks: Altering the building fabric can create unintended moisture-related issues, such as condensation and dampness, which must be carefully managed.
Because of these complexities, it’s essential to work with an experienced design team that understands EnerPHit principles and can navigate the challenges of upgrading an existing structure.
Achieving the EnerPHit standard requires several key measures, including:
High levels of insulation (either internal or external, with moisture risks carefully managed)
Triple-glazed windows and well-insulated doors
Airtight construction achieving a maximum of 1.0 ACH
Mechanical Ventilation with Heat Recovery (MVHR) for consistent fresh air supply while minimising heat loss
The certification process mirrors that of Passivhaus, requiring PHPP calculations and assessment by an accredited Passivhaus certifier. While materials and systems do not have to be Passivhaus-certified, using certified products—especially for MVHR—can streamline the process and ensure optimal performance.
To make EnerPHit more accessible, the Passivhaus Institute offers a Step-by-Step Retrofit Plan, allowing certification to be achieved in phases. This approach helps homeowners spread out costs while working towards full compliance over time.
The cost of an EnerPHit retrofit varies depending on the complexity of the building and the extent of the required work. As a guideline:
£3,500 – £4,500 per square metre is the range for a deep retrofit (excluding VAT).
MVHR installation in an average home costs approximately £12,000 - £15,000 + VAT.
High-performance windows and doors range from £400 – £600 per square metre + VAT.
However, labour-intensive aspects, such as achieving airtightness and installing insulation correctly, often constitute the largest portion of the budget. Investing in skilled professionals is crucial to ensuring the best results.
One of the biggest challenges in retrofitting is determining the optimal placement of insulation. Poorly planned insulation can lead to interstitial condensation - a hidden moisture build-up within walls that can cause mold and structural issues. Internal wall insulation is particularly risky in exposed locations where the external walls are highly porous, as it can trap moisture inside.
The Society for the Protection of Ancient Buildings (SPAB) has conducted extensive research on moisture movement in traditional buildings, advising caution when adding internal insulation to heritage or solid-wall properties. Ensuring proper moisture management is critical to the long-term success of an EnerPHit retrofit.
If you’re already planning a major renovation or home upgrade, EnerPHit offers an excellent opportunity to future-proof your property with state-of-the-art energy efficiency measures. Key situations where an EnerPHit retrofit makes sense include:
When replacing your roof or windows, allow for the integration of high-performance insulation and glazing.
If undertaking a whole-house refurbishment, giving the chance to implement airtightness measures and MVHR early in the process.
When planning an extension, enabling you to develop a cohesive long-term strategy for energy efficiency.
Even if you’re not ready for a full EnerPHit retrofit, incorporating its principles can help you achieve lower energy bills, greater comfort, and a more sustainable home.
EnerPHit is the gold standard for energy-efficient retrofitting, offering a structured approach to transforming existing homes into high-performance, low-energy spaces. While retrofitting presents unique challenges compared to new builds, EnerPHit provides clear benchmarks and design guidance to achieve outstanding results.
By working with an experienced design team, homeowners can navigate the complexities of insulation, airtightness, and moisture control to create a comfortable, resilient, and environmentally friendly living space. Although costs can vary, the long-term benefits of improved energy efficiency, lower utility bills, and enhanced indoor comfort make it a compelling investment.
If you would like to talk through your project with the team, please do get in touch at architects@risedesignstudio.co.uk or give us a call on 020 3947 5886
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