Beyond ultra-low-energy buildings are those that use, on average over the course of a year, no imported energy – zero-energy buildings – or even those that generate a surplus – energy-plus houses – both of which have been and are being successfully built.

This can be achieved by a mixture of energy conservation technologies and the use of renewable energy sources. However, in the absence of recognized standards, the mix between these – and consequently the energy-use profile and environmental impact of the building – can vary significantly.

At one end of the spectrum are buildings with an ultra-low space heating requirement that therefore require low levels of imported energy, even in winter, approaching the concept of an autonomous building.

At the opposite end of the spectrum are buildings where few attempts are made to reduce the space heating requirement and which therefore use high levels of imported energy in winter. While this can be balanced by high levels of renewable energy generation throughout the year, it imposes greater demands on the traditional national energy infrastructure during the peak winter season.