Roof pitch calculator for South Africa
Enter the rise and the run and this gives you the pitch in degrees, the ratio, the fall as a percentage and the true rafter length, then checks the pitch against the minimums for tile, thatch and sheeting.
The underlay changes the minimum, and that is the whole point
The figure most South African builders need is the tile minimum, and it is not one number. A concrete or clay tile roof is normally laid at 26 degrees or steeper without underlay. With an approved underlay beneath it, that drops to around 17 degrees.
That is a nine degree difference and it decides whether a design works. On a narrow site, or where a roof has to tuck under an existing eaves line, the underlay is often the only thing that makes the pitch achievable. It is also the detail most likely to be value engineered out by someone who does not realise it is holding the pitch up.
Thatch is its own standard
Thatch is normally laid at around 45 degrees, and it is covered by SANS 10407 rather than the roofing part of SANS 10400. It carries its own requirements on fire, on lightning protection and on the distance to a boundary, and those matter more than the pitch. Treat a thatch roof as a specialist job with a specialist standard behind it.
Sheeting minimums come from the manufacturer, not a standard
The calculator labels IBR and corrugated figures as manufacturer recommendations, because that is what they are. Roughly 5 degrees for IBR and 7.5 to 10 degrees for corrugated are the commonly quoted starting points, but the real minimum moves with the profile, the gauge, the sheet length and the end lap. A long sheet with a shallow profile needs more fall than a short one.
Sheeting is also priced and ordered per lineal metre by gauge rather than per square metre, which catches people out on the first quote.
Under 15 degrees you have a flat roof
Below about 15 degrees, South African practice treats a roof as flat, and a flat roof is a waterproofing specification rather than a covering laid to shed water. The detailing at upstands, outlets and parapets changes completely, and so does the cost. If your calculated pitch is in single figures, price it as a flat roof.
From the roof to the rest of the job
Built Simple runs your estimates, programme, crew and defects from one app. Free to start, and the calculators stay free.
Start free with Built SimpleFrequently Asked Questions
What is the minimum roof pitch for tiles in South Africa? Around 26 degrees without underlay, dropping to around 17 degrees where an approved underlay is installed beneath the tiles. Confirm against the current edition of SANS 10400-L and the tile manufacturer specification.
What pitch should a thatch roof be? Around 45 degrees. Thatch is covered by SANS 10407, which also deals with fire, lightning protection and boundary distances. Those requirements matter as much as the pitch.
What is the minimum pitch for IBR sheeting? Roughly 5 degrees is the usual manufacturer starting point, and around 7.5 to 10 degrees for corrugated. These are manufacturer recommendations rather than regulated minimums, and they change with profile, gauge and sheet length.
How do I convert roof pitch to a percentage? Divide the rise by the run and multiply by 100. A 1500mm rise over a 3000mm run is 50 per cent, which is 26.6 degrees. The calculator shows degrees, ratio and percentage together.
Is roof pitch regulated in South Africa? Tile and thatch minimums follow SANS 10400-L and SANS 10407 respectively. Sheeting minimums are manufacturer recommendations. SANS is a paid standard, so check the current edition rather than a copy on a forum.
Related calculators and guides
Sources
- SANS 10400-L, Roofs, South African Bureau of Standards. Paid standard, referenced rather than reproduced.
- SANS 10407, Thatched roof construction, South African Bureau of Standards.
- Manufacturer technical literature for profiled sheeting minimum pitches.
