passivhaus technical criteria
For any building to become a certified passivhaus it must comply with 5 technical criteria:
- The 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' and there are specific requirements for measuring this).
- The useful 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 primary energy demand for the building (which includes all heating, hot water and domestic electricity) must be less than, or equal to, 120 kWh per square meter of treated floor area per year. (Note: primary energy 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. This varies from fuel source to fuel source, which is accounted for in the PHPP.)
- 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 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.)
- Thermal comfort is ensured by no space within the building potentially experiencing internal temperatures of over 25 degrees C for not more than 10% of the total hours in the year.
Please get in touch if you have any questions regarding any of the technical aspects of the criteria above.