Roof Sheeting (IBR & Corrugated) Calculator (South Africa)

No. Every South African manufacturer datasheet checked (Global Roofing Solutions, Marley, Safintra) sets a minimum installable pitch of 7.5 to 10 degrees for corrugated sheeting, and Safintra's own Classicorr range is stricter still at 10 to 15 degrees. A 5 degree roof is below all of them, corrugated genuinely cannot be installed there without leaking. IBR686 or IBR890, on the other hand, are rated from as low as 5 degrees on a typical domestic-sized rafter run, so the same shallow carport that fails corrugated can often still take an IBR profile instead. The calculator above runs this exact pass/fail check before it shows you a single sheet count, naming the shortfall and the next profile that would work if the one you picked fails.

Because a typical pitched house roof in South Africa runs 10 to 17.5 degrees, comfortably above every manufacturer's minimum for every profile in this tool, so the pitch check almost never fires on an ordinary re-sheet. Carports, patio covers, lean-to roofs and garage roofs are a different story: they are very often built shallow on purpose, for headroom or to match an existing wall line, and it is completely normal to end up somewhere between 3 and 8 degrees. That is exactly the range where profile choice stops being a style preference and becomes a genuine buy or do-not-buy answer, at 6 degrees, for example, IBR686 needs 5 degrees or more and passes, corrugated needs 7.5 degrees or more and fails, on the very same roof.

Because that is genuinely how the South African market prices and sells this product. Every manufacturer datasheet checked for this tool (Safintra, Global Roofing Solutions, Clotan Steel, IBR World) publishes and sells sheeting by its net installed cover width already, 686mm and 890mm for the two IBR sizes in this tool, 610mm and 762mm for the two corrugated sizes, with the overlap already accounted for in that number. Clotan's own retail formula for IBR686 is simply (building length plus gable overhangs, minus a small margin) divided by 0.686m, no separate overlap addition on top. The one real trap is reading the WRONG published number off a spec sheet, the overall or formed width (737mm for IBR686, 838mm for Corrugated 762) is a different figure to the cover width and should never go into a sheet-count formula, which is why the calculator above bakes the correct cover width in per profile rather than asking you to type one in.

Because the number that actually determines your sheet length is the roof's sloped length, not the flat footprint length you can measure by walking around the building. The relationship is straightforward geometry, sloped length equals the flat plan length divided by the cosine of the pitch, but it means every calculator that skips pitch entirely is quietly asking you to supply a number, sheet length, that you cannot actually measure without climbing onto the roof. On the worked example above, a 3m flat rafter run at 6 degrees needs a 3.02m sheet length, about 0.6% more roof area than the flat footprint suggests, and that gap only gets bigger at a steeper pitch. This correction applies only to the rafter-run direction, never to the width running along the ridge, which is exactly where every published South African sheet-count formula divides straight by cover width with no pitch term involved at all.

Work out your roof's width along the ridge, add your gable end overhangs, subtract the small margin your profile's own published formula uses (70mm for IBR686, 50mm for Widespan, an unsourced 0mm placeholder for profiles with no published figure), then divide by the sheet's cover width and round up. As a worked example, a 6m wide carport roof with 300mm of total gable overhang needs 10 IBR686 sheets side by side. Separately, work out the sloped sheet length from your rafter run and pitch, that example's 3m rafter run at 6° needs a 3.02m sheet length. The calculator above does both parts for your own dimensions and profile, after first checking the pitch is even legal for that profile.

The biggest practical difference this tool found is minimum installable pitch, not looks or price. IBR686 and IBR890 can go down to 5 degrees on a typical domestic rafter run, while corrugated needs 7.5 to 10 degrees (GRS and Marley's figure, Safintra's own Classicorr range is stricter at 10 to 15 degrees). Corrugated also needs more fasteners per sheet, 3 at an internal purlin and 5 at an end or lap support against IBR's 2 and 4, confirmed directly from Global Roofing Solutions' own installation manual, not the fibre-cement rule some sources mix it up with. IBR686's rib profile is also generally considered visually 'crisper', while corrugated keeps the traditional wavy look many older South African homes and outbuildings already have. For a shallow carport or patio roof the pitch minimum usually settles the choice outright, for a normal-pitch house roof either can work and it comes down to look and budget.

Both share the same minimum pitch rule and the same fastener positions, so pitch feasibility never settles this one, width does. IBR890's wider 890mm cover against IBR686's 686mm means genuinely fewer sheets side by side for the same building width, on the 6m carport roof used throughout this page, IBR890 needs 8 sheets against IBR686's 10, 20% fewer. IBR890 also allows a wider purlin span at the same gauge, 1800mm against IBR686's 1400mm at 0.50mm, 29% more, both from published manufacturer tables, useful on a wide single span like a shed or a carport bay without adding an extra purlin. Set against that, IBR686 is the more commonly stocked size at most South African suppliers, and this tool has a real sourced sheet price for it, while IBR890 ships with an editable blank price field since no South African retail price for it could be confirmed anywhere. For a typical house re-sheet, IBR686 stays the sensible default, reach for IBR890 mainly on a wide single span where fewer purlin lines is worth it.

It depends on your gauge (sheet thickness) and profile, and South African manufacturers only publish a flat spacing-by-gauge figure, for example IBR686 at 0.50mm allows up to 1400mm between purlins on a single-span roof, per Safintra's own December 2025 spec manual. No manufacturer publishes a wind-zone-adjusted version of this table anywhere, so treat any purlin spacing figure, including the one this calculator shows, as indicative only, and have an engineer confirm it is right for your specific wind zone before you build. Critically, that manufacturer figure is a maximum you check your own purlin spacing against, it should never be the number your fastener count is built from, since on a re-sheet the purlins already exist and are countable from underneath, and on a new build you are choosing the spacing yourself. The calculator above always counts fasteners from your own entered spacing, and separately flags if that spacing exceeds the manufacturer's maximum for your chosen gauge.

More than 'one screw per rib at every purlin'. Screws are counted separately at three different positions: internal purlins (2 per sheet for IBR, 3 for corrugated, crest-fixed, confirmed from Global Roofing Solutions' own installation manual), end or lap purlins at the eaves, ridge and any end lap (4 for IBR, 5 for corrugated), and side-lap stitching screws every 600mm along each seam between neighbouring sheets, which is an additional, additive quantity, not a substitute for the crest screw already counted at that same purlin line. As a worked example, that 6m by 3m carport roof above needs roughly 174 screws in total across all three positions, rounded up to 2 boxes of 100. A commonly repeated '2 fixings per sheet width per purlin' figure is actually a fibre-cement rule (Marley Super 6, citing SANS 10237), not the steel sheeting rule used here, steel corrugated genuinely needs 3, not 2, at an internal purlin.

That flat rule, repeated on a few South African hardware sites (5 screws per m² for IBR, 7 per m² for corrugated), is an average across some unstated roof, not a number your specific roof will actually hit, because the real count depends on purlin spacing and roof size in a way a flat rate can't capture. On the 6m by 3m carport roof used throughout this page, at a fairly tight 1200mm purlin spacing, the real count works out to 9.2 screws per m², nearly double that flat rule, because a small roof has the same fixed 2 end/lap purlin lines as a big one, so those lines make up proportionally more of the total on a small roof, and side-lap stitching screws are counted on top and never appear in a per-sheet or per-m² rule at all. Space the purlins further apart, up to the manufacturer's maximum, and the per-m² figure drops toward that flat rule; space them tighter and it climbs well past it. The calculator above counts screws from your own purlin spacing and roof size instead of applying one flat number to every roof.

As a rough 2026 materials-only reference using this tool's own carport-sized worked example above, 10 IBR686 sheets plus fasteners for a 19.0m² roof comes to roughly R3 474 in DIY materials, not including flashings or any professional labour. For comparison, having an existing roof professionally re-sheeted, materials and labour both, typically runs R385 to R770/m² in South Africa as of 2026, which works out to roughly R7 317 to R14 633 for that same roof, a genuinely different scope to the bare materials figure, not a like-for-like comparison. A full strip-and-recover job, replacing underlay and insulation as well as the sheeting, runs a good deal higher again, roughly R750 to R1,300/m². The calculator above works out your own DIY materials total and shows it next to the professional installed range, with that scope difference labelled rather than blended into one number.

Ridge caps along the roof's ridge line, plus barge, apron or general cover flashing whereever a sheet edge meets a wall, gable or another roof plane. South African suppliers sell these as discrete pre-cut pieces, not by the running metre, Cashbuild's IBR ridge cap comes in 3000mm lengths at roughly R298 each, its general cover flashing in 1800mm lengths at roughly R43 each, while Robhar's full galvanised range (sidewall, headwall, corner, valley, drip and more) all comes in 2450mm lengths at R50 to R135 depending on type. Whichever you use, the honest way to cost a flashing run is to round the metres you need up to whole pieces and price those, never to convert to a per-metre rate as the primary figure, since that is not how the product is actually sold. The calculator above does exactly that for both supplier ranges.

Mostly yes, with one limit worth knowing. The profile geometry, minimum pitch and purlin spacing figures come from named manufacturer datasheets (Safintra, Global Roofing Solutions, Clotan Steel), and every price in the calculator, sheet price, fastener box price and flashing piece price, is fully editable so you can match your own supplier's quote exactly. The limit is IBR890, which two different manufacturers sell under different names with slightly different rib geometry and purlin spans, Global Roofing Solutions calls its version IBR890/Supa-Clad and that is the geometry this tool ships, Safintra's equivalent product is called Fluteline 7 and has marginally different numbers, so if you're pricing off a Safintra quote specifically for that particular width, double check the purlin spacing against Safintra's own figures rather than this tool's.

Run it once per separate roof plane and add the resulting shopping lists together, the same approach this site's decking and ceiling calculators use for an L-shaped deck or an irregular room. Each plane of a hip roof, or each bay of a multi-bay carport, can have its own width, rafter run and even its own pitch, so treating them as one combined footprint would blur exactly the pitch-dependent slope correction this tool exists to get right. Any shared ridge or hip line will come out slightly conservative on fasteners when counted once on each plane's own edge, which is the safe direction to be wrong in.