APP or SBS — the choice that matters
| APP modified | SBS modified | |
|---|---|---|
| Modifier | Atactic polypropylene | Styrene-butadiene-styrene |
| Behaviour | Plastic — harder, higher heat tolerance | Elastic — stays flexible when cold |
| Best for | Exposed roofs taking full Cape sun | Decks that move, colder or shaded roofs |
| Typical thickness | 3mm – 4mm | 3mm – 4mm |
| Indicative | R220 – R350/m² | R260 – R380/m² |
For most Cape Town roofs a 4mm APP membrane is the right answer, because UV and heat are the dominant loads here rather than freeze-thaw movement.
The details that decide whether it lasts
- Side laps 100mm, end laps 150mm. A visible bead of molten bitumen should squeeze out along every lap. No bead means no bond.
- Upstands minimum 150mm. Carried up every parapet, wall and kerb, then chased in and sealed at the top. Membrane stopped short at a wall is the single most common cause of a leak that appears to come from nowhere.
- Break-joint the second layer. The top sheet must be offset so its laps never coincide with the laps below.
- Outlets dressed in. Membrane taken into the outlet, not merely up to it.
- Primer over the whole deck. Not just the lap lines.
Ask to see the roof before the second layer goes down. Every one of the points above is checkable with your own eyes and none of them are visible afterwards.
Where torch-on is the wrong choice
Torch-on is not universal. It is the wrong system on a timber deck with no fire break, on a roof with dozens of small penetrations where a liquid-applied membrane detailing in better, on a trafficable balcony where a polyurethane system handles foot traffic and movement, and on any below-ground wall, where water arrives under pressure and needs tanking or a cavity drain membrane instead.
Common questions
How much is torch-on waterproofing per m² in Cape Town?
About R220–R380 per m² for a two-layer 4mm system including primer, upstands and cleanup. Single-layer work is cheaper but is a repair, not a system.
How long does torch-on waterproofing last?
Two-layer 4mm APP membrane, correctly lapped and not ponding: 15–20 years. Single layer laid straight over an old system: expect three to five.
Is torch-on safe to install?
It uses an open gas flame, so it requires a competent crew, a fire watch, and care around timber, waterproofing solvents and roof penetrations. It should not be laid directly onto combustible substrates without a fire-break underlay.
Can torch-on be walked on?
For maintenance access, yes. For a balcony or deck in daily use it needs a protective screed and tile, or a polyurethane system designed to be trafficked.