The weight with which we tread upon the planet is not just about how we heat and insulate our homes, important though that is. It is also about how we move about, about how the ‘form factor’ (or shape) of our buildings affects their thermal efficiency and about the durability and residence of the places and buildings that we create. It’s not very sustainable to create a place and destroy it less than 20 years later as happened to much post-war development. New towns should be sustainable places that last and make it easy to tread lightly. The evolving requirements of attractive buildings in the future should encourage future residents to find new uses for them, not pull them down after one generation as we have done with so many unpopular post-war buildings.