Green patina roofs
Is the charming vintage green an aesthetic choice or a natural outcome?
Montreal is a city of architectural wonders, and I’ve always been captivated by the bright green roofs of its historic buildings. Like scattered pieces of jade, they add a unique charm to the city’s skyline.
Green Patina
Ever wonder if those green roofs were painted for aesthetics or maybe even for religious reasons? Turns out, they're not painted at all! That lovely green hue, called verdigris, is actually a result of copper's natural oxidation process.
Copper, often used in roofing, reacts with oxygen, moisture, and air pollutants over time, creating that signature green patina. For centuries, copper has been the go-to material for important public buildings, churches, universities, and even homes. Its flexibility makes it perfect for forming over domes or curved roofs.
Key Element
So, what actually turns copper from pink to brown, and eventually green? Acid rain! Sulfur dioxide and nitrogen oxides in the air play a huge role. Back when coal was king, it took about 8-10 years for copper roofs to turn green in the 1960s. In the late 1800s, it took around 20 years as coal use was just picking up.
The green roofs of the Parliament Hill's West Block in Ottawa have been replaced with the bright shiny pink new copper roofs in 2018. Due to today’s cleaner air, we have to patiently wait for about 30 years to see the iconic green roofs again. But the green is worth the wait!
Legend
There’s an old legend that horse urine was used to speed up the greening of the Parliament Hill’s Center Block when it was rebuilt after a fire (1916-1919). Why? Well, the oxidation layer protects the copper. And with no cranes or trucks back then, horses were everywhere, so it made sense!
Reference(s)
I love the patina on these roofs! I had no idea about the horse wee.......x
I love patina and I love the green roofs just like you. I had no idea they were copper either. In Hermann Missouri in my latest post there were copper domes on the courthouse, which stood out wherever you could see them in the city. I am wondering why those did not turn green now. Regardless I absolutely love the ones you shared in your post.