Old slates and asbestos: what to know before the roof check

Natural slate is stone. An artificial slate or corrugated sheet is cement in sheet form, often grey, red or pink. Only that last kind can be asbestos cement.

OVAM states that a roof or facade of artificial slates or corrugated sheets from before 1990 always contains asbestos. Material from 1945 to 2001 may contain it. That is most likely for what was made between 1955 and 1985.

Do not break, drill, grind or sand them. Do not remove moss, and do not clean them with a pressure washer. Those actions release fibres.

A new layer over the old slates is not, according to OVAM, a solution for an asbestos-cement roof. Cleaning is not either. For that roof, OVAM describes replacement as the only option.

Do not use rainwater from such a roof for cleaning or for watering the garden. The water carries particles with it.

A honeycomb texture or white spots can point to asbestos cement. If you do not see those signs, asbestos is not ruled out. A photo of the outside is not enough.

If the home already has an asbestos certificate or an asbestos inventory, the application is listed there. Otherwise a certified asbestos expert or a laboratory establishes it. A flame test or a home kit is not a reliable method, according to OVAM.

The roof check looks at whether the roof is dry and whether a repair or a replacement is the question. It does not establish whether the slates contain asbestos.

In greater Antwerp, older houses often still have artificial slates. First the identification, then the roofing work. The Flemish action plan expects asbestos-cement roofs and facades to be replaced by 2034. The current rules sit with OVAM.