Which Wall Material Has the Best U Value?

A large, steeply gabled family home with impressively low build costs
(Image credit: Jeremy Phillips)

What exactly is a U value and why do architects, self builders and energy-efficiency experts get so excited about it?

Put simply, U values measure how easy it is for heat to pass through a structure (or its ‘thermal conductivity’), so the lower the number the better. To put it another way: low U values mean that only a small amount of heat is escaping through your walls, windows or floors.

Tim Pullen

Tim is an expert in sustainable building methods and energy efficiency in residential homes and writes on the subject for magazines and national newspapers. He is the author of The Sustainable Building Bible, Simply Sustainable Homes and Anaerobic Digestion - Making Biogas - Making Energy: The Earthscan Expert Guide.

His interest in renewable energy and sustainability was first inspired by visits to the Royal Festival Hall heat pump and the Edmonton heat-from-waste projects. In 1979

this initial burst of enthusiasm lead to him trying (and failing) to build a biogas digester to convert pig manure into fuel, at a Kent oast-house, his first conversion project.

Moving in 2002 to a small-holding in South Wales, providing as it did access to a wider range of natural resources, fanned his enthusiasm for sustainability. He went on to install renewable technology at the property, including biomass boiler and wind turbine.

He formally ran energy efficiency consultancy WeatherWorks and was a speaker and expert at the Homebuilding & Renovating Shows across the country.