How the roof shapes a building’s energy performance

Around 40% of the energy consumed in the EU is used in buildings.¹ As one of a building's largest surfaces, the roof can play an important part in how much energy is needed for heating and cooling. So how does the roof influence a building's energy use and running costs, and why does that matter for existing buildings as energy rules tighten?

During the colder months, heat naturally escapes from a building, including through the roof. In an uninsulated home, around a quarter of all heat is lost this way, according to the UK’s Energy Saving Trust. While that figure applies specifically to homes, it shows just how much difference the roof can make. Adding insulation helps keep heat inside and reduces the need for heating.²

Insulation plays a key role in a roof's energy performance. Its performance is often expressed as a U-value, which indicates how much heat passes through a building element. The lower the U-value, the better the insulation.

Insulation doesn’t only matter when it’s cold. In summer, it helps keep heat out and reduces the amount of energy needed to cool the building.

The roof surface can play a role too. Light-coloured roofs reflect more sunlight instead of absorbing it, keeping the surface cooler and potentially reducing cooling demand. This effect is strongest in warm climates and less significant during summer in the cooler parts of Northern Europe.

There is a trade-off, however. In winter, a reflective roof also absorbs less heat from the sun, which can increase heating needs. And when a roof is already well insulated, a reflective surface alone has virtually no additional impact on indoor comfort. Good thermal insulation has a much greater influence than the colour of the roofing membrane. So while roof colour can make a difference, whether it actually saves energy depends largely on the climate and the insulation beneath it.

That makes insulation particularly relevant when an existing roof is due for renovation. Adding or upgrading it can reduce heating demand and lower energy bills,² while also helping to reduce cooling costs during warmer months. The roof’s performance also depends on its condition. If moisture gets into the build-up, the insulation can lose some of its insulating value, so heating and cooling systems may have to work harder.

And improving existing roofs will only become more important. Around 80% of today’s buildings are expected to still be standing in 2050, while around 75% of the EU building stock is currently energy inefficient.¹ When an existing roof is renovated, upgrading the insulation alongside the waterproofing can help improve the building’s energy efficiency.

It’s not only energy use and running costs that are putting existing buildings under the spotlight. EU legislation is pushing in the same direction. The revised Energy Performance of Buildings Directive, which entered into force in May 2024, covers the building envelope, including insulation and windows. For existing buildings, the focus is on the worst performers first: the aim is to renovate the 16% worst-performing non-residential buildings by 2030 and the 26% worst-performing by 2033.¹

Each member state implements the directive through its own legislation, so the exact requirements vary from country to country.¹ The roof is part of that envelope, which makes it an important consideration when improving the energy performance of an existing building.

Sources
¹ European Commission, Energy Performance of Buildings Directive. https://energy.ec.europa.eu/topics/energy-efficiency/energy-performance-buildings/energy-performance-buildings-directive_en (consulted 24/09/2026) (EU)
² Energy Saving Trust, Roof and loft insulation, 2026. https://energysavingtrust.org.uk/advice/roof-and-loft-insulation/ (consulted 24/09/2026)