What is EnerPHit?
What is EnerPHit? What is a Passive House? Why should I care? What makes it so cool?
What Is EnerPHit?
EnerPHit is an adaptation of the Passive House framework, a scientifically proven building methodology, that applies to retrofit projects and acknowledges that, in an existing structure, there is a practical limit to the amount of structural change that can be made. The standard significantly expands on the legal minimums and aims to reduce heating and cooling energy demand by up to 90% and manage excessive internal temperatures, helping to provide a house that is comfortable for its occupants and sustainable for the environment.
What Are The Key Principles?
Airtightness: ≤ 1 Air Change per Hour
This quantifies how much air can leave the house (leading to heat loss) or enter the house (leading to draughts). To achieve this rate, the building should be effectively fully enclosed with an appropriate airtight barrier and all penetrations are carefully sealed. Passivhaus Trust have an excellent guide on airtightness, including a 1:1 scale guide of how big holes can be per m².1Space Heating Demand: ≤ 25 kilowatt-hour per square metre per annum (kWh/m²/a)
This governs how much energy is required to heat the property to at least 20°C and is principally managed by improving the building fabric. This goes far beyond topping up the loft insulation, and includes insulation under the ground floor and wall insulation - depending on space and planning, this can be either internal or external wall insulation.Primary Energy Renewable: ≤ 60 kilowatt-hour per square metre per annum (kWh/m²/a)
This is a measure of a building’s total energy demand given a future environment where the grid supply consists solely of renewable sources and covers all elements of the building, including lighting, cooking and other domestic appliances. A more energy efficient house places a lower demand on the grid and reduces the peak energy requirements, effectively capitalising on low carbon, renewable sources such as wind and solar.Frequency of Overheating: ≤ 10% per annum
This is the measure of the percentage of hours that a building’s indoor air temperature is above 25°C over a period of 1 year. The goal is to ensure designers adequately consider the placement of windows, the total surface area of windows and ventilation techniques to ensure occupant comfort in a warming climate.Ventilation: ≥ 30 cubic metres per hour per person (m³/h/person)
If Airtightness is about preventing heat loss through uncontrolled air movement, then ventilation is about reintroducing controlled air movement to improve indoor air quality and manage humidity.
Quality Control
Quality Control is perhaps the most crucial part of the Passive House and EnerPHit process. The standard places a significant emphasis on a full survey and measurement, with extensive modelling undertaken in the Passive House Planning Package - a meticulously prepared spreadsheet that documents all the criteria for a successful certification and has been proven to deliver reliable results. This is then reflected on-site through an almost obsessive level of attention to detail to ensure the reality reflects the modelling, with photographic evidence of everything collected to enable third party auditing.
Why Are We Aligning To It?
We have two principal reasons for implementing EnerPHit - firstly, it’s philosophical. We firmly believe that we are in a climate emergency and that reducing our demand for energy whilst also transitioning to renewable sources is an achievable way of contributing (in part) to efforts to limit the effects of climate change.
The second reason is admittedly a little more selfish - social and political events have led to fuel and food bills increasing dramatically in recent years; and we’d also like to be more comfortable, without having to bury ourselves under blankets or be turning the thermostat up constantly!
How Will We Implement It?
Having done hours (days!) of research and reading, we visited both The National Self Build & Renovation Centre and a regional home building show to see practical examples of key building details and confirm that this was an approach we wanted to pursue. We then spoke to multiple accredited Passivhaus caonsultants before appointing a local design and build agency. They’ll guide us through the process of designing and building our extension, as well as shaping the detailed design decisions that are required to bring the house up to EnerPHit standards. We’ll be documenting and sharing the process here as we go through it.