The watertightness solution depends on the type of roof and the fixing system used. In all cases, the point where the screw penetrates the roof must be properly sealed to prevent water ingress.
On metal roofs with direct fixing, watertightness is achieved by combining butyl tape with a correctly installed screw fitted with an EPDM washer. The butyl tape creates a sealing barrier between the elements in contact, while the EPDM washer seals the screw penetration point as it is compressed against the surface. MS sealant can optionally be added for extra protection.
On tiled roofs — and on metal roofs when a hanger bolt is used — watertightness requires a screw with an EPDM washer and mandatory sealing with MS sealant. The sealant must protect the penetration point and complement the seal provided by the washer.
Correct tightening is essential in both systems: the EPDM washer must be properly seated and compressed, without gaps or deformation. Insufficient tightening can leave pathways for water ingress, while overtightening can damage the washer and reduce its sealing capacity.
It is also important to check that the fixing is suitable for the material and thickness of the substrate.
Therefore, there is no single solution suitable for every type of roof: for direct fixing on metal, butyl tape and an EPDM washer must be combined, with MS sealant as an optional addition; when fixing with a hanger bolt, the EPDM washer must always be complemented with MS sealant.
To learn about other factors that can cause water ingress and the solutions available to protect the roof, see our guide on how to prevent leaks in photovoltaic installations.