What is a U-value and how are they calculated?

two men calculating u-values in house
(Image credit: Getty)

Despite it now being a common term, the question 'what is a U-value?' still has some people puzzling — but we are here to here, whether you are insulating a wall or build a new home from scratch, to explain all.

The thermal envelope of a home is made up of all the elements that separate the internal conditioned space from the external unconditioned air. This is primarily to protect us from the cold in the winter, but is also useful in protecting us from uncomfortable heat in the summer. The way that we measure the performance of each of the parts that make up this thermal envelope (roof, walls, floor, windows and doors) is with a measure called the U-value.

paul testa
Paul Testa

Is an architect, the director of HEM Architects and a specialist in low energy design.

Paul Testa

Architect Paul is the director of HEM Architects and a specialist in low-energy design. HEM Architects are well-versed in designing sustainable, energy-efficient new builds and extension schemes. He has also just completed an eco retrofit to his family home.

He taught the technology course for the MArch in Architecture at Sheffield University, and is a tutor for the Sustainable Architectural Studies Masters course.