Least recognisable - The Hespeler Library, Cambridge, Canada

The Hespeler Library was originally built in 1922 at a cost of $14,500, funded by the Carnegie Foundation. Kongats Architects won a 2010 Zerofootprint Re-Skinning Award for its work, which aimed to showcase the old building while giving it a contemporary facelift. Mid 20th-century additions were demolished to reveal the original structure, and then an insulating glass 'display case' was built around the building. A double layer of ceramic frit glass reduces solar heat gain. A third internal layer filters sunlight through a hand-woven textile that depicts the town's industrial past. The changes have improved the library's energy efficiency by 67%.

Most attractive - Unilever House, London

The goal here was to keep the aesthetics of Unilever's neoclassical headquarters intact, breathing "new life into a stunning but under-performing [Grade 2] listed building". Arup's solution preserved 60% of the original building, behind its spectacular fluted-column façade. Original fittings, such as the parquet flooring, were retained or reused, and any unwanted furniture was donated to schools and charities. The refurbished building now features a landscaped roof garden and spray taps, innovations that reduce the peak flow of waste water into the local sewer. One of the most significant energy reductions comes from an efficient cooling system. The building earned a BREEAM 'Excellent' rating.

Most improved - 100 Princedale Road, London

This domestic retrofit smashed its targets, cutting carbon emissions by 83% and energy use by 94%, and scooping a Green Apple Award. It saves the tenants £910 a year in utility bills. It was designed to Passivhaus standards, with the first triple-glazed sash windows to be installed in the UK, alongside wall insulation. It has no boilers, radiators or heating system, featuring solar thermal panels for warm water and an innovative underground heat exchanger for warmth and ventilation.

Largest scale - 1200 Buildings Programme, Melbourne

The City of Melbourne and the Victoria Government, Australia, have set a goal to refurbish 1,200 commercial buildings to reduce emissions, use less water and create healthier work environments. It's being touted as the largest transformation in the city for 160 years, and hopes are high that it will generate AU$1.3 billion in economic activity. The project's flagship is 530 Collins Street, owned by GPT Wholesale Office Fund. Its retrofit involved new boilers and cooling towers, a combined heat and power plant, and ultra-efficient lighting, and reduced greenhouse gas emissions by approximately 4,700 tonnes a year.

By Anna Simpson at Green Futures

This article originally appeared in Green Futures, the magazine of independent sustainability experts Forum for the Future. Images courtesy of glenn, torroloco, Martin Pettitt, and Shiny Things on flickr