The Great Debate: Single Ply vs. Double Torch-On

All right. Kia ora, tēnā tātou katoa. My name is Shane Clark, I'm the general manager here at Nuralite and here we are bringing you webinar number... it felt like 723 but probably more like 50 or so. Today's topic is on membrane selection and it's about single-ply TPO versus double-layer torch-on. We've nicknamed it the great debate. It's a great debate amongst architects and designers in the industry, it's a great debate amongst applicators and tradesmen alike, and it's also a great debate internally here at Nuralite. So we have a very strong advocate for single-ply TPO here - Hilton from Zimbabwe. Hello team how are we. And we have an equally strong passion for double-layer torch-on from Rod from Lenfield. Hello everybody. Today's webinar we try to make it as interactive as possible. There's a Q&A section at the end so feel free to type in your questions. We've had a few questions come in since we posted the notice about this webinar. This webinar is set for five NZIA CPD points. At the end there'll be a survey that goes out and for those looking for CPD points we can issue those. That's about the webinar I think. It's set for about 30 minutes, we'll see how long these guys go for. It's an internal webinar today - no external consultants, just an internal battle so it'll be more light-hearted than usual. Let's kick off. We're talking about single-ply TPO versus double-layer torch-on. The key takeaway is there is no silver bullet when it comes to membrane solutions. Different applications, situations and weather conditions favor one over the other. There's no wrong answer but they have different advantages. Hilton, tell us about the TPO product. TPO stands for thermoplastic polyolefin, which is a modified plastic forming the membrane. The membrane is 1.52mm thick with a reinforcing scrim. Rolls come in 3.6m wide by 30m long for smooth back, and 3m by 30m for fleece back. We heat weld the seams to create watertight bonds and adhere it to substrates like plywood or concrete using TPO glue. Rod, tell us about your product. We have a bituminous membrane - polymer modified bitumen glass reinforced. This is a two layer system - a 3mm base sheet available in self-adhesive, torch-on, vented or fully bonded options, and a 4mm cap sheet in slate, white or charcoal. Combined you have a 7mm double reinforced system. Let's run a quick poll - as a designer or specifier, what's your current preference - single-ply or double-layer torch-on? The results are in - starting at exactly 50/50. Now let's run through some scenarios. First scenario is a residential apartment building - four stories high, about 1000m² roof area with around 40 small balconies. Rod, torch-on first. Double-layer torch-on all the way for durability. Balconies face heavy post-installation traffic - the 7mm system handles this better. We've altered our details to use single layer cap sheet at thresholds to avoid height issues. Hilton, same situation with TPO. The sheet size means fewer seams - often just one joint per balcony at the high point. For builder protection we can stage installation, leaving threshold laps until last. Alternatively use old carpet protectors or install walkway rolls - 750mm wide TPO with tread pattern. Next scenario is a big box retail space - 3000m² warm roof on metal tray substrate. Hilton, TPO approach. Fleece-back TPO installed with robotic welding for speed - large sheets mean fewer seams. All penetrations handled with TPO pockets and counterflashing's. Rod, your turn. Two-layer torch-on - self-adhesive base sheet first then torched cap sheet. The 7mm system provides acoustic benefits - much quieter in rain. Both systems have all necessary accessories. Price difference? Hilton says it depends on applicator efficiency - TPO can be faster on large areas. Rod notes torch-on installation can be equally competitive. Product costs per square meter are actually similar between the two systems. Third scenario - gutters on a commercial warehouse. Rod says torch-on is ideal for durability against foot traffic in gutters. Offset laps between base and cap sheets eliminate leak paths. Hilton counters that TPO's 3.6m width allows long runs with minimal seams in gutters. Walkway rolls can be added for permanent protection. Fourth scenario - heritage refurbishment. Hilton emphasizes TPO's flame-free installation is safer for historic buildings. Rod explains their self-adhesive base sheet eliminates torch risk at that layer, with temporary shields used when torching cap sheet. Both systems can overlay existing roofs with proper preparation. Final scenario - green roofs. Rod's torch-on system includes root inhibitor and handles the abuse from gardening activities. Hilton concedes TPO isn't recommended for intensive green roofs but can be used with ballasted systems. Quick fire round: Both systems are compatible with electronic leak detection, have BRANZ appraisals and CodeMark certification. Minimum falls are 1:80 for both. Both can collect potable water with proper filtration. Both are compatible with warm roof builds. Torch-on has 40+ years history in NZ, TPO nearly 20 years. Both carry 20 year warranties. Key points: Thicker membranes (7mm torch-on) generally offer more durability, but TPO's 1.52mm with reinforced scrim performs well. Lighter colors perform better - TPO maxes at dove gray while torch-on offers white, slate and charcoal options. There is no single best solution - the right choice depends on project specifics. Q&A highlights: Both systems handle penetrations well with specialized details. TPO may require less maintenance due to smooth surface. For solar installations, white membranes are recommended for reflectivity. Cost differences depend more on installation factors than product costs. Final poll shows a shift to 60/40 favoring TPO after the discussion. The real answer remains that the best choice depends on the specific project requirements. Thanks all for attending - CPD survey links will follow. The discussion then moved into more technical specifics about membrane composition. Hilton elaborated on the TPO formulation: "The polymer blend we use contains specific UV stabilizers and antioxidants that give us the 20-year warranty confidence. The scrim reinforcement isn't just fiberglass - it's a proprietary woven matrix that provides dimensional stability across the temperature range from -40°C to +120°C." Rod countered with torch-on's material science: "Our modified bitumen uses SBS polymers at 18-22% content by weight, giving that perfect balance of flexibility and tear resistance. The mineral surfacing isn't just for looks - those ceramic-coated chips reflect about 35% of solar radiation compared to smooth surfaces." A detailed exchange followed about installation tolerances: Shane Clark: "What about substrate imperfections? How forgiving are these systems?" Hilton: "TPO requires substrate deviations less than 6mm over 3m. We can accommodate some unevenness with the fleece-back version which has more conformability." Rod: "Torch-on is more forgiving - up to 10mm over 3m because the molten bitumen can bridge minor gaps. But critical to properly prepare the substrate either way - no loose particles, properly cured concrete, etc." The conversation turned to climate considerations: Audience Question: "Which performs better in high wind uplift zones?" Hilton: "TPO assemblies can achieve 6kPa wind uplift resistance when fully adhered and perimeter secured. The key is the continuous bond - no air gaps underneath." Rod: "Our torch-on systems test even higher - up to 8kPa when using our specially formulated high-tack adhesives. The weight of the system itself (about 9kg/m²) provides inherent resistance." Shane Clark: "What about extreme thermal movement?" Hilton: "TPO has a linear expansion coefficient of 1.2mm per 10°C per meter. We design expansion joints accordingly." Rod: "Bitumen expands too, but our reinforcement and installation methods accommodate this. The key is proper detailing at perimeters and penetrations." The discussion covered fire performance: Hilton: "TPO achieves Group 1-S spread of flame when tested to AS/NZS 1530.3. The formulation includes fire retardants." Rod: "Our torch-on systems exceed Building Code requirements with Group 1 ratings. The mineral surface provides inherent fire resistance." An extensive Q&A session followed with over 30 questions from attendees. Key exchanges included: Q: "How do you handle complex roof shapes like hyperbolic paraboloids?" Hilton: "TPO's flexibility allows for complex geometries, but requires careful detailing. The 3.6m width helps minimize seams on curved surfaces." Rod: "We'd approach it differently - breaking complex shapes into manageable sections with proper flashing transitions. The malleability of hot bitumen helps conform to curves." Q: "Maintenance requirements over the lifespan?" Rod: "Torch-on benefits from annual inspections, clearing debris from drains, and checking flashings. Every five years a professional inspection is recommended." Hilton: "TPO is similar though the smooth surface may require less frequent cleaning. Critical to check seams and penetrations regularly." Q: "End-of-life recyclability?" Hilton: "TPO is 100% recyclable - we have a takeback program where old membrane gets reprocessed into new products." Rod: "Bitumen membranes can be recycled into roading materials or processed for energy recovery. We're working on improved recycling pathways." The session concluded with final thoughts: Shane Clark: "After this deep dive, any parting advice for specifiers?" Hilton: "Consider the whole system, not just the membrane. Proper design, substrate preparation, and installation quality are equally important regardless of which membrane you choose." Rod: "Don't default to what you've always used. Evaluate each project's specific needs - sometimes TPO will be better, sometimes torch-on. We're happy to advise case by case." Shane Clark: "Perfect note to end on. Thanks to our panelists and all attendees. Remember to complete the survey for your CPD points. Until next time."