By at least one estimate, the buildings U.K. architecture firm Architype has designed since its inception 25 years ago have produced 35% less carbon dioxide than comparably sized structures built to code.

And while some Architype designs incorporate renewable-energy installations, the superior performance of its buildings derives largely from an emphasis on airtight shells, thorough insulation, passive solar gain, and natural ventilation – essential precepts of Passivhaus design. That approach, and the firm’s longtime commitment to the use of sustainable materials, earned it a 2009 Ashden Award during a ceremony in London last month.

Architype, with offices in London and Hereford, was one of two finalists in the Ashden Awards for Sustainable Energy’s business category, and won a prize of 15,000 pounds (about $24,000 U.S.). Awards also were given to charities, schools, and local governments for sustainable-energy achievements, and in international and outstanding-achievement categories.

Established in 2001, the Ashden Awards are intended to both publicize the work of green-building advocates and practitioners and help them further develop that work.

As noted in an Ashden Awards press release, Architype hasn’t stopped trying to improve the performance of the projects it works on: the buildings in its portfolio that are scheduled for completion in the next two years are expected to be 65% more energy efficient and generate 75% less CO2 than they would if they were built to code.