A Commercial Waterproofing Guide for South African Businesses
Is Your Roof Ready for the Rainy Season?
A commercial roof is ready for the rainy season when its waterproofing is intact, every lap, joint, fixing and penetration is sealed, and the gutters and outlets can carry a storm's worth of water off the roof. The time to check is before the first heavy rain, not after it. Waterproofing needs dry weather to apply and cure, and roofing contractors are fully booked once the leaks start.
- Inspect and repair the waterproofing before the rains, while the weather still allows it to cure.
- Most leaks start at the details: laps, fixings, flashings, parapets, penetrations and outlets.
- Blocked drainage can turn a sound roof into a leaking one in a single storm.
- When the rainy season starts depends on where your building is.
When Is the Rainy Season in South Africa?
It depends on where your building is. Most of the country, including Gauteng, the Free State, North West, Mpumalanga, Limpopo and KwaZulu-Natal, gets most of its rain in summer, roughly from October to March, often as short and intense afternoon thunderstorms. The Western Cape is the opposite, with its rain arriving in winter on cold fronts. The Garden Route and parts of the Eastern Cape coast can get rain in any month.
Summer Rainfall
Roughly October to March across the interior and the east. Intense thunderstorms, often with hail, that test drainage hardest.
Winter Rainfall
Roughly May to August in Cape Town and the south-western Cape. Long spells of rain and strong winds driven by cold fronts.
All-Year Rainfall
The Garden Route and parts of the Eastern Cape coast. With no reliable dry season, work is planned around the forecast.
Wherever your building is, the rule is the same: waterproofing work belongs in the dry months before the rains arrive.
What Should a Pre-Season Waterproofing Check Cover?
The waterproofing itself, the details where it most often fails and the drainage that carries water off the roof. On commercial roofs, leaks rarely start in the middle of a sheet or slab. They start at laps, fixings, flashings, parapets, penetrations and outlets, where the waterproofing has to bridge a joint or turn a corner, and where movement and sun wear it out first.
Metal Roofs
- Side laps and end laps sealed, with no rust bleeding from the joints
- Fixings tight, with sound washers and no rust around the heads
- Coatings intact, without peeling, cracking or bare patches
- Flashings, ridge caps and roof lights sealed along every edge
Flat Concrete Roofs, Balconies and Parking Decks
- Membranes and coatings free of blisters, splits and open seams
- Upstands at parapets and walls sealed and properly finished off
- No ponding: water still standing 48 hours after rain points to a drainage or fall problem
- Outlets and expansion joints sealed and clear
Gutters, Outlets and Downpipes
- Gutters and box gutters cleared of leaves, dust and debris
- Box gutter linings or coatings intact, with no rust holes
- Outlets and downpipes flowing freely, with guards in place
- Overflows in place, so a blocked outlet does not send water into the building
"The middle of a roof rarely leaks. Joints, laps, fixings, parapets and outlets do, because that is where the waterproofing has to bridge a gap or turn a corner."
Which Waterproofing Repairs Should Be Done Before the Rains?
Anything that lets water in now, and anything that will once heavy rain arrives: open laps and failed sealant, loose fixings, cracked or blistered membranes, lifted flashings and rusted gutters. Small defects are cheap to fix in dry weather and expensive once water has reached the insulation, the ceilings and the stock, so the dry months are the time to deal with them.
- Joint and seam sealing: laps, fixings and fastener points treated, the most common source of leaks on metal roofs
- Torch-on membrane repairs: splits, blisters and open seams on flat roofs and parapets repaired or overlaid
- Liquid-applied membranes: seamless, flexible coverage for flat roofs, complex details and areas prone to ponding
- Gutter linings and repairs: rusted box gutters lined or repaired before they are carrying a storm
- Flashing and parapet sealing: the perimeter details where the roof meets a wall
Our waterproofing page explains the five systems we install and how the right one is chosen for each roof, and our gutters and downpipes service covers box gutter linings and repairs. Where a metal roof's coating has worn through across large areas, performance coatings restore the protection over the whole roof rather than patch by patch.
Most waterproofing products need a dry surface and dry weather to cure. A coating or membrane applied to a damp roof, or rained on before it has cured, can fail early. Do not leave the work until the rainy season has started.
What If the Rains Have Already Started?
Deal with active leaks first, then plan the permanent waterproofing for the next dry spell. Temporary sealing can stop water coming in, a leak diagnosis can find where it is actually entering, and the full system can follow once the roof is dry enough to take it. Coating a wet roof to save time usually means paying for the work twice.
Water often enters at one point and travels under the sheeting or through the insulation before it appears, so a roof leak diagnosis is worth doing before any repair. If a storm has already damaged the roof, our guide to industrial roof storm damage sets out what to do in the first 48 hours.
How Far Ahead Should You Book Waterproofing?
Book the inspection six to eight weeks before your region's rainy season, so there is time to quote, schedule and finish the work in dry weather. Contractors' diaries fill quickly once the first storms arrive, and the week after a big storm is the worst possible time to be looking for a waterproofing crew.
- Eight weeks before: inspection and a written condition report with photographs
- Six weeks before: quotes compared on the same specification and guarantee
- Four weeks before: repairs and waterproofing scheduled and under way
- Before the first rain: gutters and outlets cleared and a final check of the details
Sicon Group waterproofs industrial, commercial, retail and multi-unit residential buildings across all nine provinces, using torch-on, liquid membrane, cementitious, polyurethane and reflective coating systems, backed by guarantees of up to 20 years. A planned roof maintenance programme keeps that protection ready season after season, and our guide to roof coating quality control explains what to check before you sign off the work.
Frequently Asked Questions
When should I waterproof my commercial roof?
In the dry months before your region's rainy season. For summer-rainfall areas such as Gauteng and KwaZulu-Natal, that means late winter and early spring. For the Western Cape, it means summer. Waterproofing needs dry conditions to apply and cure properly.
Can a roof be waterproofed in the rain?
No. Most waterproofing systems must be applied to a dry surface and need dry weather to cure. During the rainy season, active leaks can be sealed temporarily and the permanent waterproofing done in the next dry spell.
How often should commercial roof waterproofing be checked?
At least once a year before the rainy season, and again after any severe storm. Flat roofs, balconies and parking decks that carry foot or vehicle traffic benefit from more frequent checks.
Which waterproofing system is best for a commercial roof?
It depends on the roof's slope, substrate, exposure and foot traffic. Torch-on membranes suit sloped roofs and areas with foot traffic or mechanical stress, liquid-applied membranes suit flat roofs, complex details and areas prone to ponding, and cementitious systems suit concrete. A roof assessment decides which is right.
Get Your Roof Rain-Ready
Book a pre-season waterproofing inspection. We will check the roof, the details and the drainage, and fix what needs fixing while the weather still allows it.