About this calculator
The ceiling insulation R-value and area you need to meet the SANS 10400-XA roof requirement for your energy zone.
How it’s calculated
SANS 10400-XA (as updated in 2021) sets a minimum total roof R-value of 3.7 m²·K/W in energy zones 1 to 7, and 2.7 in zone 5H, the humid coastal strip that includes Durban (figures from Pelican Systems). The roof covering and ceiling add a little: SANS 10400-XA:2011 tables 8 and 9 give a metal sheet roof R0.30 and a clay tile roof R0.35 with heat flowing up (R0.36 and R0.48 flowing down, in the humid zone), and the ceiling R0.05. The insulation itself must make up the rest; for other coverings, such as concrete tiles, use your designer’s or the maker’s figure. Buy a product whose stated R-value meets that figure, and check its coverage per roll or pack.
Worked example
With these inputs:
- Area length
- 8 m
- Area width
- 6 m
- Energy zone (SANS 10400-XA map)
- Zones 1 to 7: total roof R3.7
- Roof covering
- Metal sheeting, e.g. IBR (SANS 10400-XA table 8)
- Waste allowance
- 5%
the result is:
- Ceiling insulation
- 51 m² of R3.35 or better
- Required total roof R-value
- R3.7
- Roof covering and ceiling
- R0.35
- Insulation R-value needed
- R3.35
- Ceiling area
- 48 m²
Tips from the trade
- New buildings and qualifying alterations must meet the SANS 10400-XA roof R-value for their energy zone. Find yours on the official energy zone map.
- Keep insulation clear of eaves vents and recessed light fittings unless they are rated for contact.
- Board out over the top layer only if you raise the boards on legs. Compressed insulation loses performance.
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.