A version of the ultra low-energy Passivhaus standard is being developed for refurbishment projects, Building can reveal.

Under the German standard, which is growing in popularity in the UK, the energy used for space heating must not exceed 15kWh/m2 a year. The airtightness target is 0.6 air changes an hour.

The standard for refurbishments, called EnerPHit, relaxes conditions in certain key areas: the heating demand must be below 25kWh/m2 a year and the airtightness is one air change an hour.

Zeno Bastian of the Passivhaus Institute confirmed plans to launch the EnerPHit standard early next year and said it was being piloted on a handful of schemes in Germany.

A number of UK architects are already lining up to get schemes accredited. These include two projects by Bere Architects and a low-energy refurbishment by Prewett Bizley Architects as part of the Retrofit for the Future campaign.

The Passivhaus standard for new build demands extremely high levels of insulation and airtightness - many times stricter than the level expected by Building Regulations. It can be hard to achieve this in refurbishments, however, where the building’s orientation and the size of windows cannot be altered.