Which system your roof needs
| Roof type | System | Indicative | Service life |
|---|---|---|---|
| Flat concrete deck | Two-layer torch-on membrane | R220 – R380/m² | 15 – 20 years |
| Complex flat roof, many penetrations | Liquid acrylic, fibreglass-reinforced | R120 – R240/m² | 8 – 12 years |
| Trafficable deck or podium | Polyurethane membrane + screed | R450 – R800/m² | 10 – 15 years |
| Sound existing bitumen | Liquid rubber re-coat | R95 – R180/m² | 5 – 8 years |
| Pitched tile roof | Point, seal, replace and underlay repair | Quoted per repair | — |
| IBR / corrugated sheet | Seam sealing and fastener replacement | R80 – R160/m² | 5 – 10 years |
A re-coat over a failed system buys you one winter. If the membrane below is blistered, delaminated or holding water, it has to come off.
How a flat roof is done properly
- Strip and inspect the deck. Failed membrane off, screed checked for soundness and for water trapped inside it.
- Correct the falls. A roof that ponds will fail again regardless of the membrane. Screed-to-fall at a minimum of 1:80 toward the outlets.
- Prime. Bituminous primer across the whole deck so the membrane bonds rather than sits.
- First layer torch-on. Fully bonded, 100mm side laps, 150mm end laps.
- Second layer. Laid to break joint with the first so no lap sits above a lap.
- Upstands and details. Membrane carried a minimum of 150mm up every vertical, dressed into outlets, and terminated into a chased and sealed edge.
- Flood test. Outlets plugged, roof flooded, held and checked before anything goes back on top.
Signs your roof needs work now rather than next year
- Blisters or bubbles in the membrane — water is already trapped underneath
- Laps lifting at the edges, especially on the south-east corner
- Membrane gone hard, grey and crazed — the bitumen has lost its oils to UV
- Ponding that is still there 48 hours after rain
- Rust staining or plant growth at the outlets
- A brown ring on the ceiling below that grows every winter
If you already have a stain on the ceiling, start with roof leak repair — the leak is not always above the stain.
Common questions
How much does roof waterproofing cost in Cape Town?
A two-layer torch-on system on a flat concrete roof runs about R220–R380 per m² including primer and upstands. A liquid acrylic system runs about R120–R240 per m². Access, the state of the existing screed, and whether falls need correcting are what move a quote most.
Can you waterproof over an existing membrane?
Only if the existing membrane is fully bonded, dry, and not blistered. Torching a new layer over trapped moisture drives it into the deck and the new system fails within two seasons.
What is the minimum fall for a flat roof?
1:80 toward the outlets is the practical minimum. Below that a roof ponds, and standing water shortens the service life of every waterproofing system available.
How long does the job take?
A standard domestic flat roof of 60–100 m² is typically two to four working days, plus a dry window before starting. Torch-on cannot be laid on a damp deck.