Roof Sheet Calculator — South Africa
Calculate IBR or corrugated roof sheets for any SA roof. Sheet count, ridge lengths and end-lap allowances — IBR 686 and corrugated 762 profiles.
⚠️ For planning purposes only. Always have a registered roofing contractor verify quantities and structural requirements before ordering.
Roof Sheet Calculations in South Africa — IBR vs Corrugated
IBR (Inverted Box Rib) and corrugated sheeting are the two dominant metal roofing profiles in South Africa, found on millions of residential and commercial buildings. Getting the sheet count right before ordering is critical — ordering too few means a second delivery at extra cost, and trying to match a sheet profile from a different batch or supplier can result in colour and gauge mismatches that are visible from the street.
SA Roof Sheet Profiles — Key Specifications
| Profile | Cover Width | Effective Cover | Min Pitch | Purlin Spacing |
|---|---|---|---|---|
| IBR 686 | 800mm nominal | 686mm | 5° (approx 1:12) | 1.2–1.8m (0.47mm) |
| Corrugated 762 | 900mm nominal | 762mm | 8–10° | 0.9–1.2m (0.47mm) |
| IBR 686 (thicker) | 800mm nominal | 686mm | 3° | Up to 2.4m (0.58mm) |
Roof Sheet Calculation Formula
Sheet runs = CEIL(Roof width ÷ Effective cover width)
Sheets per run = CEIL(Rafter length ÷ (Sheet length − End lap))
Sheets per slope (net) = Sheet runs × Sheets per run
Total sheets = Sheets per slope × Number of slopes × Wastage factor
Roof area (m²) = Roof width × Rafter length × Number of slopes
End Laps — Why They Matter in SA Conditions
The end lap is the horizontal overlap between two sheets along the same rafter run. In South Africa, the minimum end lap for IBR and corrugated sheets is 150mm for inland areas on roofs with a pitch of 15° or more. In coastal regions, high-rainfall areas, or on lower-pitch roofs, this increases to 200mm. An insufficient end lap is one of the most common causes of roof leaks in South African buildings — wind-driven rain can travel up under the lap on low-pitch roofs during severe storms.
Side Laps and Ridge Caps
The side lap (overlap between adjacent sheets widthways) is built into the effective cover width calculation — one rib of the IBR sheet or one corrugation of the corrugated sheet overlaps the adjacent sheet. Ridge caps are ordered by linear metre — measure the total ridge length and add 10% for overlaps between cap pieces. Ridge caps are typically 1.8m long in SA. Valley flashings, barge boards and other accessories are ordered separately based on the specific roof geometry.