At the end of 2019, about 40 houses were completed in East Flanders, all with the same execution standard. The edges of the flat roofs were finished with a bead in natural zinc, an L-profile for covering, with 21mm plywood underneath (type: 'WBP Meranti').
There was no problem until November 2022: reports of loose eaves. A site visit by the roofer quickly revealed the problem ... the plywood turned out not to be waterproof after all.
However, the construction board was sold by the dealer as "WBP" (1), so the roofer assumed that the board was suitable for damp environments. In retrospect, nothing could be further from the truth: the construction board was not WBP adhered, with all its consequences.
Due to the humid climate in the cavity, the plywood panels began to delaminate. This also completely removed the stability from the eaves and the structure. In strong winds, the eaves even began to shake.
(1: WBP means that the plywood is glued with an adhesive that can withstand a 72-hour boiling test. In those 72 hours, the plywood must not delaminate. More info on WBP can be found here.)
Perhaps all the eaves on the 40 homes will have to be replaced. Specifically: Taking off zinc work, roofing and plywood to then completely rebuild. Whoever ends up footing the bill will be best to sit down when receiving the final invoice. (Cost for the roofer here was calculated at 24,000 euros)
This case shows that it is essential for roofers to choose a plywood with warranty. Then, as a craftsman, you can be sure of consistent composition. Still a rotten panel somewhere, or a case of delamination? Enjoy your conclusive warranty and don't pay the bill yourself.
