The Hidden Threat to Roof Terrace Systems: How Raaft’s Solution Stops Corrosion in Its Tracks

At Raaft, we’ve engineered a solution: powder-coated joists that form the backbone of our roof terrace systems. In this blog we will explore how this innovative coating acts as a protective barrier, why it matters in mixed-metal environments and how it contributes to the longevity and performance of your roof terrace.

What is galvanic corrosion and why does it matter for roof terraces?

Galvanic corrosion, also known as bimetallic or dissimilar metal corrosion, is an electrochemical process where one metal corrodes when in contact with another metal through an electrolyte.

This occurs when two different metals are electrically connected in the presence of a conductive solution, like moisture.

So why does this matter when designing your roof terrace?

Roof terraces are constantly exposed to the elements, in particular, rain, condensation and even high humidity. When dissimilar metals such as steel or aluminium are used in proximity without proper separation, moisture can act as a conductive bridge which can lead to accelerated corrosion.

Over time, this can:

• Weaken structural components
• Reduce the lifespan of the terrace
• Result in costly maintenance or replacements

On rooftop terraces, where space is limited and materials are layered tightly together, even small instances of galvanic corrosion can cause significant issues. That is why choosing the right materials and using effective protective measures is crucial.

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Common causes of galvanic corrosion in roof terrace systems

Galvanic corrosion in roof terrace systems is not just about using the ‘wrong’ metals, it is often the result of how materials are combined, installed or exposed to the environment.

Here are some of the most common causes:

1. Contact between dissimilar metals: When metals like aluminium, steel, copper and zinc are used together in structural components, such as joists or pedestals, and make direct contact, they can cause a galvanic reaction if moisture is present.
2. Moisture accumulation: Rain, condensation and standing water provide the perfect electrolyte needed to complete the galvanic circuit. Poor drainage or trapped water between layers of materials increases the likelihood of corrosion.
3. Lack of protective barriers: Inadequate or missing layers, such as powder coatings, allow metals to touch directly. This can accelerate galvanic corrosion.
4. Poor installation practices: Improper fastening, cutting protective coatings during installation or failing to seal connections can expose bare metal surfaces and create contact points for corrosion to happen.
5. Environmental exposure: Coastal areas with salty air, industrial zones with pollutants and locations with high humidity levels intensify galvanic corrosion risks. In these environments it is particularly vital to have protective layers, like powder-coated joists, in place to prevent corrosion.

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How Raaft’s aluminium joists address galvanic corrosion

At Raaft, we have engineered our roof terrace systems with durability and longevity in mind. A key part of that is protecting against galvanic corrosion. By pairing powder-coated aluminium joists with high-performance, zinc adjustable pedestals, we have created a system designed to thrive in challenging environments.

Powder-coated aluminium joists

Aluminium is naturally resistant to rust, is lightweight and ideal for outdoor applications.

When it comes into contact with other metals like steel or zinc, in the presence of moisture, galvanic corrosion can still occur.

To prevent this, Raaft applies a robust, architectural-grade powder coating to every aluminium joist. This coating serves two critical purposes:

1. Physical separation: It creates a layer that prevents direct contact between dissimilar metals. A key condition required for galvanic corrosion to begin.
2. Moisture barrier: It seals the surface of the aluminium, protecting it from rain, condensation and environmental moisture that would act as the electrolyte in the corrosion process.

The result is a highly durable joist that maintains its structural integrity and appearance over time. This makes them ideal even in harsh, high-moisture environments like rooftops, coastal areas or exposed urban terraces.

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Long-term benefits: Durability, safety, and reduced maintenance

Specifying the right materials is not just about performance on day one. It is about ensuring that performance lasts for years to come. Raaft’s use of powder-coated aluminium joists brings a range of long-term benefits that translate into real value for developers, architects and building owners.

1. Enhanced durability: By preventing galvanic corrosion, our system maintains the strength and stability of structural components over time. Powder coating protects the joists from weathering, UV exposure and chemical damage.
2. Improved safety: Structural integrity is not just a maintenance issue; it is also a safety issue. By eliminating corrosion risks, our system helps avoid premature failure or degradation of critical support elements.
3. Reduced maintenance costs: Galvanic corrosion can result in hidden damage that is costly to identify and to repair. By designing corrosion resistance into the roof terrace system from the start, Raaft reduces the need for frequent inspections, replacements and emergency fixes.
4. Future-proofing your project: With increasing pressure on the built environment to meet higher standards of performance and longevity, Raaft’s corrosion-resistant design contributes to the sustainability and efficiency of your project.

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