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Copper Roofs & Their Patina

If you live in or around Toronto, you may have wondered about the changing colour of the roof on one of the city’s most famous landmarks, the classic Old City Hall.

For as long as most people reading this post can remember, Old City Hall’s roof was a light green colour. It was the same colour as the domed roof on another Toronto landmark, St, Lawrence Hall; and the same colour as many world landmarks, including the Statue of Liberty.

But, starting in 1997, Old City Hall’s roof colour began to change and it was completely brown by 2005.

What Happened to the Roof on Old City Hall?

Like on any “home”, the roof needed replacement. Installed in the late 1920s, Old City Hall’s roof was made of copper and the fact that it lasted about 70 years reinforces copper’s reputation as one of the most durable roofing materials.

The new roof is copper too. The difference in colour from the green of the old roof to the brown of the new roof are due to a tarnish that forms over time on copper, many other metals, stone and stained and finished wood.

The tarnish is called patina and very often it protects the material below to help it last longer. It’s a big reason why copper roofs are so durable. .

The City of Toronto began replacing the copper roof on Old City Hall in 1997 and the new copper has not yet acquired its patina, which can take many years to form, depending on the climate. So that’s why the roof’s colour changed.

Copper is also a desirable roofing material due to its pliability, which makes it easier to work with and bend into the different shapes needed for the roof. That pliability is why it was chosen as the “skin” of the Statue of Liberty, where it was shaped into the statue’s arm, facial features and gown.

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