Puumerkki is a Finnish supplier of wood-based construction products and solutions, serving construction professionals in Finland and the Baltic countries. Completed in May 2025, the company’s new premises in Vantaa, Finland, are designed to efficiently support the storage and distribution of wood-based building materials. The building also houses office space for sales and support functions.
The concrete stairwell connecting the first and second floors was intended to feature a new striking Effex® wood panel. However, its own fire-retardant treatment alone did not meet the strict fire classification requirements for an emergency exit route.
Because Puumerkki’s project manager for construction and industrial projects, Sami Karttunen, is familiar with a wide range of products through his work, he suggested complementing the structure with fire-retardant WISA®-SpruceFR plywood. The panel meets the best possible fire classification for wood-based products B-s1, d0.
The architect revised the structural calculations, confirming that the solution complied with fire safety regulations. A support frame was installed on the concrete wall, and WISA-SpruceFR was mounted to provide a stable base for the desired wood paneling. Even though the plywood remains hidden, it plays a crucial role in the structure.
“WISA-SpruceFR plywood was a perfect fit for this project. As a fire-rated material, it enabled us to use the surface finish we wanted. I also knew from experience that we could fully rely on its availability and delivery, even with a tight schedule,” Karttunen says.
WISA-SpruceFR can replace multi-layered constructions
Traditionally, fire-safe constructions are built using multi-layered solutions that combine several different materials.
“When needed, WISA-SpruceFR can replace more complex structures. This helps save time, labor and materials,” says UPM Plywood’s Product Manager Riku Härkönen.
The fire-retardant treatment does not compromise the technical properties of the plywood. WISA-SpruceFR is just as strong and easy to work with as untreated spruce plywood and can be used in the same applications.
Spruce plywood is particularly well suited for load-bearing structures. Fire-retardant WISA-SpruceFR does not require any special construction methods or additional treatments to achieve its fire classification. Its fire-retardant performance remains effective even if there is an air gap behind the panel.
In the Puumerkki stairwell, a frame was installed on the concrete wall, onto which the fire-retardant WISA-SpruceFR was mounted. The decorative wood paneling was then attached to this stable base.
“The FR plywood met all the requirements and enabled us to use the surface material we wanted. At the same time, we saved time and costs because it’s a ready-made, certified solution that’s readily available,” says Karttunen.
Environmental declarations add value
An added benefit is that all WISA spruce plywood products come with third-party verified Environmental Product declarations (EPDs). These documents provide reliable information about the environmental impacts of the manufacturing process.
“When you have a fire-rated product that also comes with an easily accessible EPD, it strengthens the perception of both the supplier and the material as trustworthy. UPM has been a pioneer in environmental documentation since 2019, and the climate impact of its products has improved positively over the years,” Karttunen notes.
A legal reform coming into effect in 2026 will further increase the importance of EPDs, as construction projects will be required to include product listings and climate impact assessments.
“With this information, designers and builders can compare products, improve the sustainability of their operations, and report their progress credibly,” Härkönen concludes.