Why Does Copper Roofing and Cladding Turn Green? (Patina Development)

One of copper’s most distinctive traits is its transformation from a shiny red to a striking, trademark green. 

This is the result of a natural chemical process, called patination. 

Patination has made copper one of the most popular materials for metal roofing, with this trademark colour change being used to bring a bold design feature to properties across the country. 

In this guide, our metal roofing experts have provided a quick guide to understanding why copper roofing and cladding turn green, including how this quality impacts the design of these metal roofing systems. 

What causes copper roofing and cladding to turn green? 

When copper is exposed to oxygen and moisture (both present in the air), the metal oxidises, forming copper oxide. 

Over time, this layer of copper oxide continues to react with water, carbon dioxide and other substances in the atmosphere. 

This process of patination results in the copper turning green in colour (which is the result of a combination of copper carbonates and hydroxides that are formed in this reaction). 

Interestingly, the exact shade of green that forms on the copper varies from location to location. This is because different environments (and the chemistry that exists there) can alter the reactions that take place, resulting in different proportions of compounds. 

For example, in areas with higher levels of pollution (e.g. industrial areas), sulfur compounds can create a deeper, darker shade of green in the copper. 

Then, in coastal locations, the higher salt levels lead to a greater presence of chloride ions, which can bring a turquoise hue to the copper. 

We’ll cover the development of patina – and how it is affected by different conditions – more in the next section. 

Understanding copper roofing design and effects

Patina can develop in a range of different ways, depending on the conditions that the roof is in. 

Then, the way that the patina develops can have a significant impact on the overall visuals of the copper roofs and cladding.

Factors that you should be aware of include:

• The colour evolution – When your copper roof is first installed, it will be bright and shiny. Then, over the first few months and years, it will gradually darken to brown. From there, you will see it eventually turn a bluish-green.
• Variations in colour and tone – As the patina formation depends on the roof’s microclimate, the same copper roofs can look different over time, if they are located in different settings. Levels of rain exposure, pollutants and salt spray in the area can all affect the ultimate colour of the patina. 
• Ageing periods – Different parts of the roof’s surface can age unevenly. For example, vertical surfaces, overhangs and sheltered areas may patinate at different speeds, compared to the main body of the roof. 
• The ability to accelerate and control patination – If the property owner wants the green colour to be achieved quickly, you can work with your installer to add a chemical treatment to the roof, which speeds up the roof’s ageing process. 

What benefits does patina bring to copper roofs? 

Using copper in roofs and architecture unlocks a range of valuable benefits, both in terms of aesthetics and functionality. Many of these advantages are down to the way copper forms a patina. 

These benefits include:

• High durability, thanks to the additional protection – A common misconception is that a patina is a sign of corrosion damage. In reality, the patina actually forms a protective barrier. This helps to reduce the speed of the copper’s degradation, including slowing down any further chemical reactions.
• Increasing the roof’s lifespan – This extra protective layer also helps to extend the lifespan of copper roofs and cladding. As a result, these elements can last for decades (and even in some cases, over a century).
• Low maintenance requirements – Copper roofing is naturally a low maintenance material, but once the patina has formed, this quality becomes even more pronounced. With the patina, copper roofs almost self-stabilise, and usually you don’t need to repaint or refinish the roof. 
• Stylish aesthetic – The green patina gives the roof a bold, timeless aesthetic, creating a fantastic statement feature piece. 

At Salmon Solutions, we offer premium quality copper roofing solutions, to suit all styles, budgets and requirements. 

Our talented team of metal roofing specialists can work with you, to find the perfect match for your specific context. To learn more about our products, or about the ageing process for copper roofs, chat to our team.