Gauteng Province in South Africa is infamous for its spectacular and severe hailstorms. Every few summer seasons, some part of Johannesburg gets hit with a hailstones which are sometimes described as the size of golf balls and this is not far from the truth. These storms shred trees, kill birds, damage cars, break windows and even injure people and pets if they cannot immediately find shelter.
They also cause millions of rands worth of damage to roofs and waterproofing. Herewith is a brief overview of the different types of roofs and the varying damage that can be caused.
Metal roofs
Metal roofs are seldom affected. Due to the toughness and rigidity this is probably the best performing roof when it comes to not being damaged by hail. At worst some minor pock marks may occur. Inferior paint coatings may also be damaged. The biggest problem with hail on metal roofs is not with large hail stones, but when high volumes of small hailstones block up the fluted sections of the roof sheets, this can impede the flow of water and cause water to flow in through the overlaps. Whilst this not a common occurrence, some spectacular floods and damage to property have been caused in this way.
Polycarbonate and fibreglass roof sheets
After years in the sun, polycarbonate roof sheets can become quite brittle. When large hailstones hit these brittle sheets, they can be decimated. The bronze or clear sheets do less well in the harsh UV rays of the South African sun and these tend to be more badly affected more than the diffuser or Opal (white) sheets. The thickness of the sheets is also a factor. A 1,2mm thickness is recommended for use on flat surfaces. The 1mm thickness should only be used for sloping monitors or cladding.
Fibreglass sheets are much stronger as they contain fibreglass matting which gives greater flexural strength and better impact resistance. However if they are of thinner gauge and brittle, they can also be severely damaged in a heavy hailstorm.
Concrete tiled roofs
Concrete tiles are generally quite hail resistant. However in a freak hailstorm with gigantic stones, the tiles can smash. Even with huge hailstones, it is normally just random tiles which are affected and not every tile. However water damage can be extensive to the building interior if tiles are broken in this way.
Another fairly common problem on tiled roofs is when large volumes of smaller hailstones block up valleys and this causes water to overflow the metal flashings. Water penetration can often also be considerable in this instance. A good way to prevent this is to install a 1,5m girth heavy duty roofing plastic under the valley flashing. So if over spillage occurred, this would overflow onto the plastic liner and run down to the gutter. This would have to be undertaken by a professional roofing contractor.
Waterproofing
The two most commonly used waterproofing systems are torch on and acrylic systems. Generally a properly installed and fully bonded waterproofing system onto smooth surfaces is fairly immune. Problems occur when waterproofing is laid onto soft surfaces or there are hollow areas under the waterproofing which bridges the void instead of taking up the contour. If these areas take a hit from a medium to large sized hailstone this can cause damage. This is not usually immediately problematic, but becomes apparent over time. The usual sign is concentric ring marks on the waterproofing and if these spots are pushed in with ones finger, then almost invariably the waterproofing will depress indicating a void or hollow underneath. Dual layer torch on systems with a fibreglass upper weathering reinforcement layer are much more resistant to hail damage than the more commonly used single carrier membrane products. Other factors include the quality and age of the waterproofing system.
Acrylic systems are generally much less affected, but as with torch on waterproofing can get damaged if not fully dressed into surface undulations. Another cause is if the acrylic waterproofing membrane is not properly saturated this weakens it and makes it more susceptible.
Hail damage on waterproofing usually spells the end of the waterproofing system and will need to be replaced within a few years. This could be problematic for insurance purposes, and could well be rejected by insurance companies as the claim was not submitted immediately.
