Roofing in Gauteng

Hail: the Highveld's roof breaker

In November 2013 two hailstorms over Gauteng cost the insurance industry about R2 billion, and the storm of 28 November that year was described by PwC as the single worst insurance event in South Africa's history up to then. University of Pretoria researchers note that hailstones over 2 cm across damage roofs and cars, and stones over 3 cm damage buildings.

Their hail model expects southern Gauteng to see more than five days a year with hail larger than 3 cm, though the authors caution that it overestimates large hail. On their figures Gauteng's hail peaks in November, eases towards February and picks up slightly again in March and April. Most falls between midday and early evening.

• Plan inspections and non-urgent re-roofing for the dry winter months, before the October start of the hail season.
• After a storm, look for cracked or chipped tiles and dented sheeting, and photograph everything before repairs start.
• Ask each roofer to state the sheet thickness or tile type in writing so you can compare like with like.

Johannesburg and Pretoria have different insulation targets

SANS 10400-XA sets a minimum total thermal resistance (R-value) for roof assemblies by climate zone. The NHBRC's guide to the standard places Johannesburg in zone 1, the cold interior, where a roof must reach R3.7. Pretoria sits in zone 2, the temperate interior, where the minimum is R3.2. In both zones the rule is aimed at keeping winter heat in.

These targets apply to new houses and extensions. If you're re-roofing an older home, the roof is open anyway, so it's the moment to ask what topping up to your zone's figure would add. Our ceilings and insulation page covers the options.

Corrosion on the East Rand, lightning in the south

A national corrosion map published in the South African Journal of Science measured first-year corrosion of mild steel at about 51 µm a year in industrial Germiston, against an average of about 25 µm a year in Pretoria. Germiston's figure sits on the border between the moderate and high corrosivity classes, so on the East Rand it pays to specify properly coated sheeting and stainless or coated fixings rather than the cheapest option.

The South African Weather Service's lightning climatology recorded 10 to 15 ground flashes per km² a year over southern Gauteng. Under SANS 10400-T, a thatched building or lapa in an area with a flash density above 7 must have a lightning protection system designed and installed by a competent person. If you're re-thatching a lapa in the south of the province, budget for it.