Roof Calculator
Calculate roof area and the number of IBR sheets needed based on building footprint, pitch angle, and overhang. For South African roofing projects.
Quick Calculator Get a fast estimate
m
m
m
%
Roof Area
139,3 m²
Net Roof Area
126,6 m²
IBR Sheets (0.686m width)
204 sheets
Pitch Factor
1,082
Footprint Area
96 m²
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How to Use This Calculator
Enter your building footprint, roof pitch angle, and overhang (eaves projection). The calculator adjusts the flat footprint to actual sloped roof area using the pitch factor, and estimates IBR sheets needed.
Roof Area Formula
Pitch Factor = 1 ÷ cos(pitch°)
Roof Area = Plan Area × Pitch Factor
IBR Sheets = Roof Area ÷ 0.686m (effective sheet width)
SA IBR profile has an effective cover width of 686mm per sheet. A steeper pitch means more roofing material.
Need more detail?
Extended Calculator More options, charts, and scenario comparison
m
m
°
%
Roof Area (with waste)
121.9 m²
Plan Area
96.0 m²
Actual Roof Area
110.9 m²
Material Cost
R 22 558
Roof Weight
0.6 tons
Material Cost Comparison
| Material | Price/m² | Total Cost | Weight |
|---|---|---|---|
| IBR Sheeting | R 185 | R 22 558 | 0.6 t |
| Corrugated Iron | R 145 | R 17 681 | 0.6 t |
| Concrete Tiles | R 280 | R 34 142 | 6.1 t |
| Clay Tiles | R 380 | R 46 336 | 5.5 t |
| Slate | R 650 | R 79 259 | 3.0 t |
| Asphalt Shingles | R 220 | R 26 826 | 1.5 t |
Example Calculation
Double Garage — 6m × 6m, 22.5° pitch, 0.5m overhang
With overhang: 7m × 7m = 49 m² flat
Pitch Factor = 1 ÷ cos(22.5°) = 1.082
Roof Area = 49 × 1.082 = 53 m². With 10% waste = 58.3 m²
IBR sheets (3m length): approx 28 sheets
SA Roofing Material Costs (2025)
| Material | Price per m² | Weight |
|---|---|---|
| IBR Sheeting (galv.) | R140–R200/m² | 5 kg/m² |
| Corrugated Iron | R110–R160/m² | 5 kg/m² |
| Concrete Roof Tiles | R240–R320/m² | 50 kg/m² |
| Clay Tiles | R340–R420/m² | 45 kg/m² |
| Asphalt Shingles | R180–R260/m² | 12 kg/m² |
| Slate | R580–R720/m² | 25 kg/m² |
Need full precision?
Professional Calculator Complete parameters, sensitivity analysis, and detailed breakdown
Roof Dimensions
m
m
°
m
m
Rafter Details
5.1 m rafter length
Rafter Count (both sides)
42
Ridge Length
12.0 m
Rafter Timber Est.
R 18 274
Total Roof Area
110.9 m²
Insulation Calculator
mm
m²K/W
| Item | Value |
|---|---|
| Insulation Area | 116.4 m² |
| R-Value (nominated) | 3.5 m²K/W |
| SANS 10400-XA compliance | Compliant (≥R3.5) |
| Estimated Insulation Cost | R 7 566 |
Rain Water Harvesting Potential
mm/yr
L
| Metric | Value |
|---|---|
| Roof Collection Area | 96.0 m² |
| Annual Rainfall | 650 mm |
| Collection Efficiency | 80% (metal roof) |
| Annual Harvest | 49 920 litres |
| Months to fill 5 000L tank | 1.2 months |
Gutter Sizing
mm
#
| Item | Value |
|---|---|
| Gutters Needed (80mm/hr storm) | 1 runs |
| Gutter Material Cost (est.) | R 2 160 |
| Downpipe Cost (2 × 3m) | R 900 |
Frequently Asked Questions
The most common residential roof pitch is 22.5° to 30°. IBR corrugated iron has a minimum recommended pitch of 5°. Tiled roofs require a minimum 20–25°. Steeper pitches shed rain better but use more material and take more wind load.
IBR (Inverted Box Rib) is a popular galvanised or colour-coated roofing profile widely used in South Africa. Standard 0.47mm galvanised IBR costs approximately R140–R200/m² in 2025. Pre-painted IBR costs R160–R240/m².
SANS 10400 recommends a minimum eaves overhang of 500mm for residential buildings. A larger overhang (600–900mm) provides better wall and window protection from rain and reduces solar heat gain. In high-wind coastal areas, overhangs should be engineered to resist uplift.
SANS 10400-XA (energy efficiency) requires ceiling insulation with a minimum R-value of R3.5 m²K/W for most SA climate zones. This is typically achieved with 135–145mm blanket insulation or equivalent. Non-compliance can result in building plan rejection.