The attachment to the supporting structure has several requirements. The screw heads must be flush with the profile face. Both the screw hole and the countersink must be pre-drilled. Cracks must not form around the screw heads. The fastening means must be permanently corrosion-resistant. The length of the fasteners shall be chosen to ensure sufficient strength of the joints but shall not overhang to damage the tightness of the foil if any. The minimum distance for the screws at the ends of the boards is 3 cm minimum and 5 cm maximum from the end. This will prevent cracks from forming at the ends later on as the wood is worked. Use HOBOTEC or HAPATEC screws for spruce facade timber and HAPATEC HELI screws for Siberian and Silesian larch facade timber. HAPATEC HELI screws are suitable for facade wood made of Red Cedar, Thermo Pine, and Dark Red Meranti.