Guide · 6 min read
Selecting roofing fixings for African roofs
Drill point, thread type, coating class and sealing washer — how to build a roof fixing schedule that survives coastal salt and high UV.
Four decisions, in order
A roofing fixing schedule comes together in a fixed sequence: what you are fixing into, how thick it is, how corrosive the site is, and what the sheet profile demands. Get those four right and the part number follows.
- — Purlin material — steel, timber or concrete decides thread and point type
- — Purlin thickness — decides the drill point number, #2 through #5
- — Corrosion category — decides Class 3, Class 4 or stainless
- — Sheet profile and purlin centres — decides length and quantity per square metre
Drill point capacity
A #2 point cuts up to about 2 mm of steel, #3 up to 4 mm, #4 up to 6 mm and #5 up to 12 mm. Undersizing the point burns it out mid-hole, leaves a wandering entry and gets blamed on fastener quality. Timber purlins take a coarse timber thread with a gimlet point instead of a drill point entirely.
The sealing washer is the waterproofing
Bonded EPDM washers stay elastic through years of expansion and contraction. Loose neoprene hardens under African UV, shrinks away from the shank and leaks, usually in the third season. The difference in purchase price is small; the difference in warranty claims is not.
Installation matters too: the washer should be visibly compressed but not squeezed out from under the head. Over-driving is as leaky as under-driving.
Coating class by distance from the coast
Class 3 coated carbon steel handles most inland exposed roofing. Inside roughly five kilometres of the coast, specify Class 4 or a stainless 304 head with a carbon drill point. On the shoreline itself and on desalination or chemical plant, go to stainless 316 and budget for it at the estimating stage.
Do not forget the small lines
Side-lap stitching screws, flashing fixings, hook bolts for angle purlins, ridge and closure fixings and spare sealing washers are individually trivial and collectively the reason a crew stops work. List them on the same enquiry as the main fixings so they land in the same container.