The ecological advantage of a white roof

Painting a roof a shade of white has environmental advantages. Photo / Getty Images

When it is time to paint your roof, consider painting it a shade of white.

The idea has been slowly catching on as a way to help reduce global warming by mimicking the way that the polar icecaps reflect sunlight back into space and cool the planet.

When I lived on the North Shore, I decided to eliminate the condensation in my house by having HRV installed. But the workers discovered the insulation was wet in one corner of the ceiling cavity so the system could not be installed that day. The concrete-tile roof had sprung a leak; some tiles had shifted and others had cracked.

The problem was easily fixed and in due course the HRV was in place. In the process, I understood that the roof tiles needed to be cleaned and painted, so I organised both jobs. Learning about the White Roof Project made me choose an off-white shade. My tradie commented the job was more pleasant than when painting darker colours.

When sunlight falls on dark surfaces, much of it is absorbed and converted into heat. This heat is blocked from passing back into space because it is absorbed by greenhouse gases in the atmosphere.

While many of us have a feeling of helplessness about what we can personally do about reducing global warming, the white-roof idea gives house owners a positive action plan. Roofing companies offer a range of light colours.

Scientific research has shown a flat white roof measuring 100sq m (the size of a modest house) reflects enough sunlight to cancel about 10 tonnes of carbon dioxide emissions — roughly that put out by 2.5 cars during a year.

Under the Obama administration, federal roofs were painted white (in the US, the movement is called “cool roofs”). New York’s cool-roofs campaign passed the 9 millionth square foot of white roofs in 2018. The campaign has attracted partnerships with local businesses.

A Cool Roofs Project is also co-financed by the European Union in countries such as Greece, Italy and France.

Recently, my new, off-white corrugated iron roof was installed after six years of leaks, which were occasionally severe. The original decramastic tile roof was “rooted”, according to a FENZ worker who checked it out during a deluge in 2021. It wasn’t totally stuffed; it just leaked in two places that couldn’t be repaired. And the glue contained 0.3 per cent Chrysotile (white asbestos), which was a concern. Careful handling and disposal were required.

Eight fast-moving men in high-vis vests worked hard all day on January 12. Six of them returned the next day to complete the job and remove most of the rubbish.

White roofs are seen more and more in New Zealand, not just on houses but on large buildings like the Sylvia Park Shopping Centre in Auckland. The off-white Auckland International Airport roof is another example.

A white roof will not be suitable for every home. If your roof is overlooked by a neighbour who might find a white roof too bright, a deeper tint of off-white is recommended.

The walls of most houses in NZ are painted shades of white or cream, but why are their roofs typically green, orange or grey? For more, go to www.whiteroofs.org.nz

– Margi is a keen cyclist and adventurer. She has been the co-ordinator of Conservation Comment since 2017, and is always looking for more scribes.