Roofing decisions are made late in design and regretted early in occupation. The profile, coating, fixing method and flashing detail all have to suit the pitch, the span and the local weather, and in South Africa that varies enormously between the Highveld and the coast. This guide covers specifying roofing and metal products properly, and the handful of mistakes that cause most roof failures.
What this guide covers
- Profiles and what they are for
- Pitch minimums are not guidance
- Coating specification and coastal exposure
- Fixings and flashing: where roofs actually fail
- Insulation, condensation and the build-up
- Calculating quantities without over-ordering
- Delivery and handling
- Common and expensive mistakes
Profiles and what they are for
Corrugated and IBR remain the two workhorses of South African roofing. IBR handles lower pitches and longer spans with its trapezoidal ribs; corrugated suits shorter runs, curved applications and traditional aesthetics.
Concealed-fix systems remove exposed fasteners and suit low pitches and high-wind areas, at higher material and installation cost. They are specified where penetration through the sheet is the weak point.
Cladding profiles follow the same logic turned vertical, where the driver is appearance and weather-tightness rather than water shedding.
Pitch minimums are not guidance
Every profile has a minimum pitch, and installing below it is the single most common cause of roof leaks that no amount of sealant will fix. Water backs up under laps and finds its way in regardless of workmanship.
The minimum varies by profile and by sheet length: longer runs need more pitch, because water travels further before it clears. Confirm the figure for the specific profile and the actual run length, then design to it.
Where the architecture forces a very low pitch, the answer is a concealed-fix or standing-seam system rather than pushing a conventional profile below its limit.
Coating specification and coastal exposure
Galvanised and Galvalume both perform well inland. Coating mass, not colour, determines service life — two sheets that look identical can carry very different warranties.
Within a few kilometres of the sea, salt loading changes the calculation entirely. Step up coating specification, or move exposed fixings to stainless. The cost difference at specification stage is small against re-roofing.
Colour coating adds a finish layer and some UV protection, but it sits on top of the substrate coating that actually does the corrosion work. Ask for both figures.
Fixings and flashing: where roofs actually fail
More roof failures trace to the wrong fastener or a poorly detailed flashing than to the sheet itself. Buy the system rather than the sheet, and source fixings and hardware matched to the coating.
Fastener metal must be compatible with the sheet. Mixing metals produces galvanic corrosion that shows as rust streaking within a season and undermines the sheet warranty.
Fixing density follows the wind zone, not habit. The Cape wind regime in particular drives more fixings per square metre than inland practice, and under-fixing is the usual cause of storm damage.
Flashings, closures and ridge detail are where water enters a technically correct roof. Detail them at design stage rather than improvising on site.
Insulation, condensation and the build-up
A metal roof without a considered build-up will condense on the underside in the right conditions, dripping onto whatever sits below and being mistaken for a leak.
Anti-condensation membranes, ventilated cavities and correctly specified insulation all address it, and the right answer depends on the occupancy below.
Insulation also changes the thermal performance of the space significantly. On South African roofs the summer heat gain usually matters more than winter loss.
Calculating quantities without over-ordering
Order on covering width, never overall width. This single number changes the sheet count on every job and is the most frequent quoting error we see.
Allow for side and end laps, and confirm sheet lengths against the rafter layout before ordering so the cutting is planned rather than wasteful.
Add a realistic allowance for cutting waste around penetrations, hips and valleys. Complex roofs waste substantially more than simple rectangles.
Delivery and handling
Long sheets need suitable vehicle access and enough people to offload without bending them. A sheet creased in handling is scrap.
Store sheets off the ground, sloped to drain, and separated if they will sit for any length of time. Water trapped between stacked sheets causes storage staining that no coating survives.
Confirm access before dispatch. A failed delivery on a long-sheet load is charged twice and delays the trade behind it.
Common and expensive mistakes
Designing below the profile minimum pitch, then chasing leaks for the life of the building.
Quoting on overall width instead of covering width and under-ordering every job.
Mixing fastener and sheet metals, producing galvanic corrosion within a season.
Under-specifying coating near the coast, where salt shortens service life dramatically.
Treating flashings and closures as an afterthought rather than part of the system.
Frequently asked questions
What is the minimum pitch for IBR?
It varies by manufacturer and sheet length — IBR generally handles lower pitches than corrugated. Confirm the figure for your specific profile and run length before finalising the design.
Galvanised or Galvalume?
Galvalume generally offers better corrosion resistance for the same coating mass; galvanised is well proven and widely available. Coastal proximity is usually the deciding factor.
How do I calculate sheet quantity?
Divide roof width by the sheet covering width, not the overall width, then add for laps and cutting waste. Send us the dimensions and we will calculate it with your quote.
Which fixings should I use?
Fasteners must be compatible with the sheet coating. We supply fixings matched to the roofing so nothing is mismatched.
Do I need an anti-condensation layer?
On most enclosed occupancies, yes. Metal roofs condense on the underside in the right conditions and it is routinely mistaken for a leak.
Can you supply cut-to-length sheets?
Yes, cut to your rafter layout, which reduces both waste and on-site cutting.
How should sheets be stored on site?
Off the ground, sloped to drain and separated if stored for any period. Trapped water between stacked sheets causes permanent staining.
Do you deliver long sheets?
Yes, but confirm vehicle access and offloading arrangements when ordering — that is the usual cause of failed deliveries.
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Reference: SABS standards.
For specification support, current pricing or a delivered quote, contact Builders Store SA. Request a quote