About this calculator
Count IBR roof sheets, with purlins, ridge and barge flashing, foam closures and screws.
How it’s calculated
Panels per side = ceil(eaves length ÷ coverage width). Panel length = slope length + eaves projection. For IBR, sheets per side = (length − 70 mm) ÷ 0.686 m, as Clotan’s datasheet gives it. Purlins are spaced at up to 1,200 mm (SANS 10400-L, table 4, for 50 × 76 mm timber purlins), and each sheet is screwed through alternate flutes at every purlin.
Worked example
With these inputs:
- Roof length along eaves
- 12 m
- Slope length (eaves to ridge)
- 4.5 m
- Roof sides
- Two (gable)
- Panel coverage width
- 686 mm
- Extra length at eaves
- 50 mm
the result is:
- Roof sheets needed
- 36 sheets
- Sheets per side
- 18
- Sheet area
- 112.37 m²
- Purlin rows per side (1.2 m centres)
- 5
- Fixings
- 370 (alternate crests: 2 per sheet and 1 at the end of each row, at every purlin)
Tips from the trade
- Use the sheet’s cover width, not its overall width: IBR covers 686 mm of its 740 mm.
- Order panels cut to length. Long panels may need an end lap; check the maker’s minimum overlap for your pitch.
- Fix through the high rib or the flat depending on the profile, following the manufacturer.
- Clotan gives IBR a minimum of 5° on slopes under 30 m (7.5° above that), but SANS 10400-L allows less than 11° only on small category 1 buildings with no hips or valleys and sealed 250 mm end laps. Lay the narrow flute of each side lap uppermost and seal the laps on low pitches.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and SANS 10400 (the National Building Regulations) and your local municipality before ordering.