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Screws and bolts

Screws and fasteners for fixing new metal roofing panels to the substrate over existing roofs, such as in re-roofing (overlay, kasane-buki) construction. For steel substrates, drill screws with a drill point (pilot) at the tip are used to drill through the steel sheet without a pilot hole. For wood substrates, S-cut tips or double-thread (two threaded sections) screws hold the new roofing and the substrate together. Dedicated products for fixing over existing decorative slate or shingle roofs have a tip shape that suppresses lifting of the existing roofing material. For waterproofing, many are combined with stainless steel or steel washers and gaskets, and the surface is rust-proofed with treatments such as trivalent chromium-free zinc plating.

How to choose Screws and bolts

  1. 1. Select a type that suits the substrate

    Drill screws are used for steel substrates, S-cut tip or double-thread screws for wood substrates, and dedicated lift-prevention tip products for existing slate or shingle roofs. Each substrate type has a different structure. Confirm the existing roof construction and substrate material before selecting.

  2. 2. Check the drillable sheet thickness for steel substrates

    Drill screws have an upper limit on drillable steel sheet thickness. Listed products have an upper limit of 3.2 to 4.5 mm and a lower limit of 1.6 mm. Confirm that the thickness of the substrate steel, such as purlins, falls within this range, and also check tip specifications such as pilot length of 12 mm and cutting blade outer diameter of 3.4 mm.

  3. 3. Length suited to the total thickness of stacked materials

    Re-roofing construction passes through the new roofing, existing roofing, insulation and other layers, so confirm the maximum clamping thickness. The maximum clamping thickness of the listed product is 30 mm. Some are available in series lengths such as 90 to 150 mm. Select a length that allows sufficient engagement into the substrate beyond the total thickness.

  4. 4. Check nominal diameter and pitch

    Listed products have a nominal diameter of 4.5 to 6.3 mm and a pitch of 1.8 to 2 mm. A larger diameter gives greater holding power but also affects the hole diameter in the substrate and roofing. Also confirm the manufacturer's specified size and compatibility with the bits and drivers used for installation.

  5. 5. Compare pull-out and shear strengths

    Roofs receive uplift forces from wind suction. Listed products show values of 5.9 kN in steel substrates, 2.5 kN in wood substrates, up to 600 N in structural plywood substrates, and maximum shear of 1200 N. Use the values for each substrate in calculating the required design strength and the number of fasteners.

  6. 6. Washer material and outer diameter for waterproofing

    Washers are available in stainless steel with gasket, low-cost steel types, and others, with outer diameters of 25 mm and 20 mm. Select based on roofing profile, the area to be pressed, the risk of rainwater infiltration, and dissimilar metal contact with the roofing material. Some products are supplied as the body only without a washer.

This guide was written by AI based on the listed products' documents and specification items. Check each manufacturer's documents before adopting.