A roof edge may seem like a minor detail, but it is one of the most vulnerable parts of a roof. The sheet metal used here is exposed to moisture from the cavity, condensation, rain, and temperature fluctuations, often for years on end, without anyone paying any attention to it. If you choose the wrong material, you will pay for it later with delamination, wood rot, and expensive repairs. The choice of material is therefore more important than many people think.
In the roofing world, you see various sheet materials being used. Some are suitable, others are used because they are cheap or readily available, not because they are the best choice.
OSB
Oriented Strand Board is inexpensive and is sometimes used for roof edges, but it cannot withstand prolonged exposure to moisture. OSB absorbs moisture through its edges and then swells quickly. It may be suitable for temporary applications or dry conditions, but for a roof edge that needs to last for decades? Not a good idea.
Standard plywood (poplar or birch)
Poplar plywood is light and budget-friendly, but not moisture-resistant. Birch plywood is stronger, but has the same limitation: without the right adhesive and wood type, it is not suitable for permanently damp conditions. You often see it go wrong after a few years.
Plywood (with phenolic coating)
Plywood has a smooth, water-repellent coating and is widely used in formwork and trailers. The coating protects the surface, but not the core. If the edges are not finished properly, moisture will still penetrate. The quality depends heavily on the gluing and the types of wood used.
WBP plywood
WBP stands for Water Boil Proof – the adhesive can withstand boiling for 72 hours without coming loose. That sounds robust, but WBP only says something about the adhesive, not about the wood itself. A WBP board made from the wrong types of wood can still rot.
Guarantee plywood
This is plywood specifically designed to withstand prolonged exposure to moisture: the right types of wood (with a high durability class), WBP bonding, and a protective coating. The difference from standard concrete plywood lies in the core. Solid John offers 10 year warranty – including delamination, rot, and consequential damage.
Not every situation requires the same plate. These are the factors that determine your decision:
Type of application
A cavity wall bridge is permanently exposed to moisture from the cavity. An upstand on a flat roof is less directly exposed to moisture, but is still subject to condensation and temperature fluctuations. The more humid the conditions, the more critical the choice of materials becomes.
Thickness and span
Bij bredere spouwen of zwaardere belasting heb je een dikkere plaat nodig. Solid John Roof is beschikbaar in 15 mm en 21 mm. De 21 mm-variant is bedoeld voor grotere overspanningen en situaties zonder buitenmuur als steunpunt.
Budget versus lifespan
A cheaper panel may seem attractive, but if you need repairs after five years, it will end up costing you much more. Don't just calculate the cost of the materials, but also the labor costs and the risk of consequential damage.
In practice, we regularly see the same mistakes recurring:
If you want certainty, choose guaranteed plywood. Not because it is the most expensive option, but because it is the only one that gives you a full guarantee: 10 years against swelling, rotting, delamination, and consequential damage. This means that if something does go wrong, not only the material but also the installation of a new roof covering is covered.
Solid John Roof has been specially developed for roof edges and cavity bridging. The combination of durable tropical hardwood, WBP gluing, and phenolic resin coating makes it resistant to years of moisture pressure—without having to seal the edges.
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Can I use OSB for a roof edge?
Technically, it is possible, but not recommended. OSB cannot withstand prolonged exposure to moisture and will eventually swell and deteriorate. For a roof edge that needs to last for years, OSB is a risk.
Do I need to seal the edges of plywood?
With standard concrete plywood, the coating protects the surface but not the saw cuts. With Solid John Roof, this is not necessary: thanks to its composition, the board is also moisture-resistant at the edges.
What is the difference between WBP multiplex and warranty plywood?
WBP zegt alleen iets over de lijm: die is waterbestendig. Maar de duurzaamheid van de plaat hangt ook af van de houtsoort. Garantiebetonplex combineert WBP-verlijming met houtsoorten die van nature vochtbestendig zijn, én komt met een garantie die dat ook daadwerkelijk afdekt.
