What is EnerPHit?
While Passivhaus is, for many, the go-to standard for low-energy new builds, architect Paul Testa explains how EnerPHit, the equivalent for existing properties, could benefit renovators looking to improve the energy efficiency of their home
Many of us are familiar with the term Passivhaus — perhaps the ultimate low-energy standard for new builds. But did you know there was an equivalent for existing homes? Architect Paul Testa, who is embarking on his own EnerPHit project, explains all
Many people love their existing home for a number of reasons – the location and the neighbours, for instance – but are often faced with a dilemma when the house fails to meet certain requirements. These could include space and design but also comfort and performance. Do you move, or improve? Likewise, there are those who want to build their own home in order to have a greater influence over these elements, but struggle to find a new build plot (myself included!).
This is when we might begin to think about taking on a renovation, remodel and/or extension project. While this type of project can certainly deliver more space, what about comfort and thermal performance?
Step in retrofit. Retrofit is a form of renovation, typically undertaken to greatly reduce energy consumption. As such, retrofit involves a significant improvement in the thermal performance and comfort of your home. More specifically, it is about improving the building fabric rather than simply the introduction of renewables.
The challenge is that it is difficult to know how far to go and predict how much comfort and performance your retrofit measures will deliver. To this end, you need something to measure against and compare performance with known benchmarks. The Passivhaus standard is perhaps the best known of the energy efficiency fabric standards for new builds, and the good news is that this standard has been adapted for existing homes, too. Applying specific Passivhaus principles to an existing property on a retrofit basis can result in a high performing home — and this is where EnerPHit comes in.
What is EnErPhit?
Unlike a new home built to Passivhaus standard, when you’re considering a retrofit, many of the elements like geometry, orientation and structural approach are already decided because we’re working with an existing building. You may also have thermal bridges (or cold bridges: a path for heat to escape through gaps in insulation) that are difficult to completely eliminate.
The EnerPHit standard recognises this difficulty and sets the required performance at a lower level than Passivhaus to accommodate working with existing buildings.
To achieve EnerPHit you must achieve a space heating and cooling demand of 25kWh/m2/year (compared to the Passivhaus standard of 15kWh/m2/ year) and instead of an airtightness performance of 0.6 air changes per hour you need to achieve 1.0 (the Building
More than 85% of the homes that will exist in 2050 are already built, and a huge percentage of our energy usage and carbon emissions comes from our homes. If we’re going to meet our 2050 carbon reduction targets, then retrofitting existing properties is going to play an important part.
Regs for new homes require between 5 and 15 according to the Chartered Institution of Building Services Engineers). We’re talking about the same Passivhaus comfort but utilising slightly more energy. It is still a huge improvement on most existing homes and even new builds.
EnerPHit offers a benchmark for renovators to work to. Like Passivhaus, we use the Passivhaus Planning Package (PHPP) design tool (see below left for more) when designing an EnerPHit scheme. This helps us to deliver more efficient buildings at an early design stage, considering orientation and geometry. The PHPP also allows us to make informed decisions about where to spend money and to understand what cost and energy implications there are in various retrofit measures and the alternatives that might be being considered.
Retrofitting is not easy, however, and EnerPHit is a tough standard to achieve; the thermal and airtightness strategies are likely to be more complex and more difficult on site than with a new build. You may have to balance the pros and cons of internal or external insulation, and potential moisture issues that come from changing the building fabric. More so than ever, it demands a skilled and informed design team.
That said, perhaps the ultimate benefit of aiming for the EnerPHit standard and for full certification is the rigour and quality assurance it demands. Following the criteria ensures that the works are completed in the way they are designed; that the airtightness performance is achieved and that there are no fudges along the way.
Anecdotally, from talking to other architects and consultants, having a defined certification standard to achieve actually makes it an easier team effort; there’s no accepting a slight slip in performance and the whole team has a shared goal.
When carrying out an EnerPHit, there will be a list of measures required in order to meet the standard. These will involve:
• High levels of insulation — either internal or external, although internal needs more care in terms of moisture risk.
• High performance triple-glazed windows and external doors.
• Careful consideration of window installation.
• An airtightness reading of 1.0.
• A mechanical ventilation with heat recovery (MVHR) system.
As the standard you’re working to is a recognised benchmark, in order to receive EnerPHit certification, the process is exactly the same as working towards Passivhaus certification. In order to meet these requirements, the project must be designed using the PHPP and must be certified by
an accredited Passivhaus certifier. Although the products you’re including within the house do not need to be certified for Passivhaus, it does help, especially with MVHR equipment.
The cost of an EnerPHit retrofit, however, will vary, as the more complex an existing house is the more complex the retrofit will be. However, I’d recommend budgeting around £800-£1,000/ m2 for deep retrofit/EnerPHit — plus the VAT as you’re dealing with an existing building. For typical component or system costs, however, you can expect to pay around £10,000 for a MVHR unit installed in an average-sized house, and approx £400-£600/m2 for windows and doors. The big costs, though, are in labour — the installation of the insulation and airtightness measures is timeconsuming and needs to be done with care.
WhEn to takE thE lEaP
An EnerPHit retrofit makes most sense when you’re already considering renovation or remodelling work to your house. In my opinion, why not go the extra mile when you’re undertaking works anyway? Why not make the additional investment in time and materials to achieve much better performance and better comfort for yourself and your family when there’s works being carried out to your home already? Particularly in cases where you’re looking to make changes to your home and already considering improving its energy efficiency, EnerPHit makes perfect sense.
The economic argument for improving the performance of the roof when it needs replacing, or installing triple glazing rather than double-glazed windows when they need changing, is a much easier one to justify and often the numbers stack up. The key thing is to have a whole house plan from the beginning so that each measure works together in the long-term, giving you the end result of a high performing home. If you’re considering an extension, this may not be the time for you to undertake a retrofit, but it’s a great time to make a long-term whole house plan that ensures the extension works as an integral part of that strategy; it would be frustrating to find that your expensive and beautiful extension has created a barrier to a more in-depth retrofit in a few years’ time.
So if you’re considering renovation or repair works to your home with a view to achieving high levels of comfort and thermal performance, then now could be the time to plan for an EnerPHit retrofit. H