Black homes heat up and damage wood, expert warns

A black log house bought by Anu Varila’s family in Jyväskylä soon developed damaged paint and cracked wood, Yle reports. An expert warns that dark surfaces can become extremely hot in sunlight and recommends against black paint on wooden houses.

Varila and her partner were drawn to the large, modern log house, which was built in 2022 and painted entirely black. They had seen many black houses in the media and on social media, and there were several others nearby.

“Of course it looked great and somehow prestigious,” Varila says.

The family moved into the house in spring 2024, without knowing what problems the colour could cause on a sunny plot. The disadvantages became apparent soon afterwards: the facade paint had faded and deteriorated, while the log surface underneath had begun to crack.

Petri Vannula, a lecturer in surface treatment at Salpaus Further Education in Päijät-Häme, says black paint can raise the temperature of a facade to very high levels in sunlight.

He says unofficial measurements have found that the surface temperature of black-painted wood can rise above 70 degrees Celsius in 25-degree heat.

Vannula particularly advises against using black on knotty pine, knotty spruce or plastic. Resin in knots begins to liquefy and leak at around 45 degrees, he says.

Leaking resin and other extractives can create yellowish marks on the surface, but the damage is not only cosmetic. Over time, liquefied resin can also weaken the wood structurally, especially if the material is already of poor quality.

High temperatures can also cause strong thermal expansion in wood, which may, for example, warp boards.

Heatwaves in Finland are becoming longer and hotter as the climate crisis progresses. In cities, the urban heat island effect increases temperatures when limited vegetation and extensive built surfaces create areas of concentrated heat. Dark surfaces absorb particularly large amounts of heat.

Despite this, the trend for black houses continues. Vannula says black has few benefits apart from its disadvantages.

“The only thing black can help with a little is that dirt, spot mould or red mould do not show on it. And when temperatures and ultraviolet radiation are high, moss does not like to grow either,” he says.

Varila’s family decided to repaint their house in a light colour the summer after moving in, to prevent further damage to the walls. They eventually chose white.

Varila has also used her Instagram account about log houses to warn others about the disadvantages of black paint. She says the paint surface, now more than two years old, has held up well.

Vannula also advises against dark brown because it heats up. Grey paint, for example, generally requires maintenance less often.

“Black has not traditionally been used in Finland. It is simply the current trend,” Vannula says.

According to Vannula, many binders used in paint age quickly at high temperatures. Binders hold the pigment and filler together, meaning that the lifespan of black paint is often shorter, depending on the binder.

From the cities’ perspective, dark colour schemes are often linked to landscaping or the desired modern and high-quality appearance of an area. Zoning plans do not necessarily specify black directly, but may use terms such as “dark” or “adapted to the natural environment”.

Detached-house builders often want to paint their homes black even when zoning rules do not specify the colour, says Reijo Teivaistenaho, a town-planning architect for the city of Jyväskylä.

Jyväskylä’s zoning plan specifies dark colours for a detached-house area in Palokka.