The best flat roof membranes in NZ are TPO, torch-on, and Butynol, and each one wins in a different situation. TPO is the best all-rounder for new, exposed roofs. Torch-on is best for heavy foot traffic and complex detailing. Butynol is best for internal gutters.
As approved Viking Roofspec and Ardex applicators, we install all three types across Auckland. Here’s how each one earns its place.
Here’s how the three main flat roof membrane options compare on performance and New Zealand compliance:
| MEMBRANE | OUR VERDICT | BEST FOR | COMPLIANCE PATH | SEAM METHOD |
| TPO | Best all-rounder for new, exposed flat roofs | Large roofs, new builds, high-UV sites, under floating decks | CodeMark No. 30058 and BRANZ Appraisal No. 656 | Hot-air welded |
| Torch-On | Best for heavy traffic and complex detailing | Commercial roofs, trafficked decks, plant platforms | BRANZ Appraised systems (Alternative Solution) | Torch-fused, two layers |
| Butynol | Best for internal gutters | Internal gutters | E2/AS1 Acceptable Solution (within its scope) and BRANZ Appraisal No. 436 | Adhesive and butyl seam tape |
Butynol is the best flat roof membrane for internal gutters.
Ardex Butynol is a New Zealand-made butyl rubber sheet. It stays flexible as timber framing moves, and it comes in 1.0mm, 1.2mm, and 1.5mm gauges, with 1.5mm used on walk-out decks.
Its track record is hard to argue with. BRANZ recorded a 1mm Butynol roof laid in 1972 that was still in service 39 years later.
E2/AS1 only covers butyl and EPDM membranes, so Butynol offers the simplest path to council sign-off. TPO and torch-on need a BRANZ Appraisal or CodeMark instead.
This matters most in internal gutters. E2/AS1 sets out specific requirements for internal gutter linings:
Laps are bonded with adhesive and seam tape rather than fused, so seam quality depends on the installer and the weather. Cold, damp, or dusty substrates weaken the bond. Butynol is also usually laid in black, which runs hotter than white TPO.
TPO is the best roofing membrane for flat roofs on new builds, particularly large or fully exposed ones.
TPO is a single-ply thermoplastic sheet with hot-air welded laps. The seams fuse into one continuous membrane, so there’s no adhesive to break down. Light colours reflect the heat under New Zealand’s high UV, and there’s no open flame on site.
We install Viking Enviroclad, a polyester-reinforced TPO. It suits roofs, gutters, parapets, balconies, and the area under floating decks.
Enviroclad is CodeMark certified (No. 30058) and BRANZ Appraised (No. 656), which gives councils a clear compliance path. It carries a 20-year product warranty, and on eligible projects, Viking’s Full System Warranty covers product and installation together, but only when a Viking-trained and approved installer does the work.
Repairs need hot-air welding gear, so a small patch isn’t a quick job for a general roofer. It’s also a thinner membrane than a double-layer torch-on system.
Torch-on is the best flat roof membrane for roofs with foot traffic, plant equipment, or many penetrations.
Torch-on is a modified bitumen system, usually laid in two layers for built-in redundancy. The thick sheet resists punctures and moulds tightly around pipes, outlets, and upstands.
There are two main types. APP membranes handle heat and UV well, while SBS membranes stay more flexible under building movement. Viking offers APP, SBS, and hybrid APAO systems, all BRANZ Appraised.
The open flame requires hot-work controls and extra care on timber substrates. Dark cap sheets absorb heat unless they’re mineral-finished, and the system is heavier than single-ply options.
The best membrane for flat roof leaks is usually the one that matches what’s already there, or safely replaces it. An existing Butynol roof repairs best with Butynol. A failing bitumen roof is often best overlaid with a TPO such as Enviroclad FBS, which has a fleece backing designed to go over old membranes.
Most leaks start at poor falls, outlets, and upstands rather than in the middle of the sheet. E2/AS1 sets minimum falls of 2° for membrane roofs and 1.5° for decks.
Water coming through the ceiling now? Talk to our Auckland waterproofing specialists. We find the failure point first, so you fix the cause, not just the symptom.
No. Butynol is butyl rubber, and EPDM is a different synthetic rubber. Both fall under E2/AS1, but they use different adhesives, so repairs should match the original system.
We rate TPO as the longest-lasting membrane on exposed, high-UV roofs, because welded seams remove the adhesive laps where older roofs usually fail. The Building Code requires at least 15 years’ durability, and quality TPO and Butynol systems both carry 20-year manufacturer warranties.
Often yes, if the existing roof is dry, sound, and well-bonded. TPO overlays such as Enviroclad FBS are designed for it. Wet or rotten substrates must be stripped and replaced first.
Yes, but only as an Alternative Solution. E2/AS1 covers butyl and EPDM gutter linings only, so TPO or torch-on gutters need supporting evidence, such as a BRANZ Appraisal.
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