What is Gusset Plate Corrosion?

Steel Roof Truss Diagram
Diagram illustrating a typical steel roof truss system and gusset plate locations.

Gusset plate corrosion is a serious problem that is often overlooked. Protecting against corrosion to the exterior of a steel roof is usually the first task carried in any the treatment process. However it shouldn’t stop there. Every component in a roof structure plays an equally important role, including interior roof components.

What is a Gusset Plate?

A gusset plate in a roof structure is a thin triangular or rectangular piece of steel, copper or aluminium. It connects beams, chords, members and girders to form the roof truss. Bolts, rivets or welding, or a combination of all three are the most common fixing methods for gusset plates. In joints and structural locations gusset plates provide strength and rigidity to withstand the stresses of a roof structure. More commonly found in buildings and bridges they are also used in other industrial structures.

What causes Gusset Plate Corrosion?

Gusset plate corrosion in roof trusses occurs when moisture attacks the steel body of the component. This is often due to poor or lack of maintenance. Gusset plates, or roof truss connector plates, require routine maintenance just like any other roof component. When the surface coating flakes and cracks exposing the substrate to moisture ingress, oxidation will develop.

The corrosion will then spread to the rivets or bolts attaching the gusset plate to the rafters, chords and members. The roof system will now be weakened which could potentially lead to structural failure. Condensation is the main cause of corrosion. Good ventilation and regular maintenance to remove dust is therefore important to prevent the risk of gusset plate corrosion and the subsequent failure of the roof system.

Gusset Plat Corrosion Steel Roof Diagram
Diagram illustrating how corrosion in gusset plates can spread to other components if left unchecked, eventually resulting in structural failure.

How to Treat Gusset Plate Corrosion

Gusset plate assemblies are often the most complex part of a roof system. It can therefore be a lengthy process to both carry out inspections and treatments. A thorough inspection of the gusset plates is first carried out to ascertain the severity of the problem.

Here at D&D Coatings we will despatch a surveyor to assess the full requirements of the job. Once planning and health and safety preparation is complete our team of specialists will be deployed complete with equipment and materials.

With scaffolding towers and work platforms in position we begin by cleaning the affected areas. At this stage we use high-pressure washing and power wire-brushing where possible.

In certain circumstances and if its practical to do so, we employ sand-blasting to clean the plates. This removes lose and oxidised material from the gusset plates and fixings. We ensure all surfaces are sufficiently roughened to aid adhesion of the protective coatings. All damaged and severely corroded bolts and rivets are replaced.

When the areas to be treated are sufficiently sterile and clean we apply a base coat layer primer to seal the plate and other components. This is followed by a top-coat layer to match the existing colour scheme of the truss. Depending on environmental influences an epoxy or polyurethane coating will be used.

Polyurethane are often the preferred choice for top coating due to their improved mechanical properties. They also offer excellent resistance to chemical and water attack. Acrylic urethane are also suitable where colour and visual appearance is a factor.


Building managers and owners should regularly inspect roof trusses for signs of corrosion. The sooner a problem is dealt with the less costly it will be to treat. Biannual structure inspection and restoration of coatings when required will ensure the continued integrity of the roof system.

If in any doubt about the condition of your gusset plates you should contact us (or another reputable engineering consultant) for advice, we will be happy to advise.

You might also be interested in why metal roofs corrode. If you would like to find out about our gusset plate treatment services please call 01606 554040 or visit our contact page.

Please Share this Article on :