Technical Criteria - Passivhaus ‘Classic’
For any building to become a certified passivhaus it must comply with 5 technical criteria:
The specific space heating energy demand for the building must be less than, or equal to, 15 kWh per square meter of living space per year ('living space' is defined as the whole building 'treatable floor area' - there are specific requirements for measuring this).
Alternatively, the useful specific space cooling demand must also be less than, or equal to, 15 kWh per square meter of living space per year. (Note: this is not applicable in every climate, in the same way that not every climate will demand space heating.)
The specific space heating load must not exceed 10W per square meter of living space. Heating load is a measure of the instantaneous heating demand at a given moment. (Similarly to space cooling, the alternative in certain climates would be a specific space cooling load.) A building can be Certified on either the space heating (or cooling) demand or the heating (or cooling) load criterion.
The primary energy renewable demand for the building (which includes all heating, hot water and domestic electricity) must be less than, or equal to, 60 kWh per square meter of treated floor area per year. (Note: Primary energy renewable refers to the amount of energy contained in the 'raw' fuel used to provide heating, hot water and electricity for the building, prior to any conversion or transformation process, and accounts for any distribution or storage losses along the way to the building. This varies from fuel source to fuel source, and these factors are accounted for in the PHPP.) This does vary with each ‘class’ and must be reduced whenever on-site generation is factored in.
The measured airtightness level for the building must not exceed a maximum of 0.6 air changes per hour at 50 Pascals pressure (Ach50), with the building tested in both pressurised and de-pressurised conditions. (Note: These are different units, and a slightly different method, to those used in the UK Building Standards, and is approximately equivalent to a permeability of 0.75/m3/m2hr @ 50Pa. The backstop for a new-build house in Scotland is currently 7/m3/m2hr - 10 times worse, or leakier, than the maximum level required by a passivhaus.)
The overheating risk is measured to ensure that thermal comfort is achieved by no space within the building potentially experiencing internal temperatures of over 25°C for not more than 10% of the total hours in the year.
Since 2015 the Passivhaus Institut (PHI) introduced several new ‘classes’ of Certification for Passivhaus buildings. These are in addition to the standard Certification level, now referred to as ‘Classic’, and are called ‘Plus’ and ‘Premium’. In essence these are standards which incorporate on- site micro generation of energy with any surplus sent either to local storage or back to the electricity grid. In order to avoid any off-setting against a poorer building standard, these classes also require a drop in the energy demand targets: this ensures that these ultra low-energy buildings are truly energy efficient. More information on these additional classes is available on the Passipedia website.