Torch-on vs. single-ply roof membranes: what fits a BC strata or commercial low-slope roof
Both systems can protect a Metro Vancouver low-slope roof for roughly 15 to 25 years, so lifespan alone does not decide it. The one hard difference is the open flame. Torch-on SBS is a two-ply asphalt membrane welded with a propane torch, which brings a real fire risk during install but gives you puncture resistance and 2-ply redundancy. Single-ply TPO or PVC is joined with hot air, so no torch, and it usually comes as a reflective surface that handles ponding well.
Torch-on suits roofs with heavy foot traffic, mechanical service, and a non-combustible deck where the hot-work risk can be controlled with a fire watch. Single-ply suits occupied buildings where an owner would rather keep an open flame off the roof, roofs that pond, and buildings that want a cool reflective surface. On a combustible deck over occupied suites, the flame risk pushes most stratas toward single-ply. On a concrete-deck roof that gets walked hard, the durability of two asphalt plies can point the other way. Your deck, your traffic, your drainage, and your insurance decide it, not the brochure.
Why the roof deck decides more than the brochure does
Before anyone argues torch-on versus single-ply, look down at what the membrane sits on. A concrete deck and a wood or combustible deck are two different conversations. Torch-on welds the membrane with an open propane flame, and the worst-case failure is not a leak the day of the job. It is a fire that starts smouldering under the membrane, in the deck or in trapped dust, and stays hidden. Crews have packed up and gone home only to have a roof catch overnight. On a combustible deck that risk is real enough that many strata councils and their consultants take the flame off the table and go single-ply, which welds with hot air instead.
On a solid concrete deck with a proper fireproof protection sheet, extinguishers on the roof, and a fire watch that stays after the torches shut off, that risk drops a long way. So the deck type is the first fork in the road. Get that answered honestly, in writing, and half the decision is already made. A contractor who will not confirm the deck construction before quoting has not looked hard enough at your roof.
What torch-on SBS modified bitumen actually is
Torch-on is SBS modified bitumen: asphalt with SBS rubber blended in for flexibility, built up in two plies. SBS stands for styrene-butadiene-styrene, a synthetic rubber that keeps the asphalt elastic so it moves with the deck through hot and cold instead of going brittle the way older oxidized asphalt did. A base sheet goes down first, either mechanically fastened or torched, then a granular-surfaced cap sheet goes over it. The torch melts the underside of each sheet so it fuses to the layer below, and the crew rolls the lap to squeeze out a small bead of melted asphalt that shows the bond took.
Two plies means two chances to keep water out, with the laps of each layer staggered so a weak spot in one lap sits over solid membrane in the other. That redundancy is the selling point, and it is why torch-on shrugs off foot traffic and dropped tools better than a thinner single sheet. The granular cap surface also gives some protection against sunlight and abrasion. The trade-off is the flame, the weight of two asphalt layers, and the fact that cold, damp coastal weather slows the work because the asphalt has to reach the right temperature to bond cleanly.
What single-ply TPO and PVC actually are
Single-ply is one sheet of thermoplastic, either TPO or PVC. TPO is thermoplastic polyolefin and PVC is polyvinyl chloride. The sheet rolls out over the roof and gets held down one of two ways: mechanically fastened with plates and screws along the seams, or fully adhered to the substrate with an approved bonding adhesive. Then the seams get welded with hot air. A machine or a hand welder heats the overlap, and a roller presses the two sheets together so the plastic melts and flows into one continuous piece.
A good TPO or PVC weld can be as strong as the sheet itself, so the seam is not the weak link people expect. No asphalt, no flame, and the surface is usually white or light grey, which reflects solar heat. The trade-offs: a single sheet is thinner than two asphalt plies, so it punctures more easily under hard use, and the whole roof leans on that one membrane and its welds. TPO and PVC are not the same product. PVC has a long track record in standing water and stays flexible with plasticizers, while TPO is a newer chemistry whose early formulations had weathering issues that the industry has largely worked through. Ask which one is being quoted, at what thickness, and by which maker.
Systems compared
Torch-on SBS modified bitumen (2-ply)
A two-ply asphalt-based membrane. A base sheet goes down first, then a granular-surfaced cap sheet, each blended with SBS rubber for flexibility, welded down with an open-flame propane torch that melts the underside of the sheet into the layer below.
Single-ply TPO or PVC
A single sheet of thermoplastic membrane, either TPO (thermoplastic polyolefin) or PVC (polyvinyl chloride), rolled out over the roof and joined at the seams with hot air. No asphalt and no torch.
The open-flame problem on an occupied Vancouver building
This is the factor that decides more torch-on jobs than any other on occupied strata and commercial roofs. A propane torch on the roof of a building full of residents is a liability the strata carries. WorkSafeBC treats torching as hot work, which means the crew has to protect combustible material, keep extinguishers on the deck, and hold a fire watch on site after the flame goes off. The fire watch matters because a smouldering fire can take hours to surface, long after the crew would normally leave. Skip it and a roof can catch overnight.
Single-ply sidesteps the whole issue. Hot-air welding uses heated air, not a flame, so there is no asphalt melting against the deck and no smouldering-underlayment hazard. For a downtown Vancouver tower or a North Vancouver condo where the roof sits directly over occupied suites, that is often reason enough to go single-ply, even before weighing traffic or ponding. It is one fewer thing that can go badly wrong over people\'s heads.
There is an insurance angle too. Some insurers add conditions or higher premiums for torch work, and some building owners simply write open-flame torching out of their tender to remove the question. None of this makes torch-on a bad system. It makes torch-on a system that needs a controllable deck and a disciplined crew, which is a higher bar than pointing a hot-air welder at a plastic sheet.
Rain, ponding, and the coastal reality
Metro Vancouver roofs live under one of the wetter climates in the country, with well over 1,100 mm of rain in a typical year, and low-slope roofs that do not drain cleanly end up with standing water through the fall and winter. Ponding is where the two systems diverge. PVC single-ply is built to sit in standing water without breaking down, and TPO holds up well too. Multi-ply mod-bit is more sensitive to long-term ponding: water that sits for weeks works on the asphalt and the laps over time. So on a flat roof with known low spots, single-ply is usually the safer membrane.
At higher elevations on the North Shore and in the Fraser Valley, freeze-thaw adds another load. Water that ponds and then freezes expands, and repeated freeze-thaw cycles push on any weak lap or weld. A flexible SBS mod-bit and a properly welded single-ply both handle normal thermal movement, but neither likes sitting in ice at a bad detail. This is one more reason drainage comes first.
The deeper fix is drainage, not the membrane. If a roof ponds, correcting the slope with tapered insulation and clearing the drains so water sheds properly does more for the roof\'s life than any product choice. A serious roof assessment flags drainage before it recommends a membrane, because a new roof that still holds water is a roof you will be back on sooner than you should be. Our team scopes drainage, deck condition, and detailing together, which is the same approach we bring to any waterproofing project on a Vancouver roof or deck.
Reflectivity, heat, and cool roofs
A dark roof absorbs sunlight and runs hot. On a summer afternoon a black mod-bit surface can reach temperatures far above the air temperature, and that heat radiates down into the top-floor suites and up into the assembly. White TPO and PVC reflect a large share of that solar energy, so the surface stays cooler, the top floor is more comfortable, and the cooling load drops. On a big open commercial roof or a top-floor residential roof with a thin assembly, that difference is noticeable.
Torch-on can get there too, but it needs help. A reflective granulated cap sheet or a reflective coating applied over the mod-bit brings the surface temperature down. That is an extra material and an extra step, and the coating has to be maintained and re-applied over the roof\'s life. Single-ply gives you the reflective surface built in. If summer heat gain is already a complaint in your building, that weighs toward single-ply or toward budgeting for a reflective surface on a torch-on roof.
How each system fails, and the part owners never budget for
Neither system usually fails in the middle of the field. They fail at the details. On torch-on, the common failure is a lap that never fully bonded, often because the asphalt was too cold or the crew moved too fast, and it opens years later as a slow leak. Flashings at parapets, drains, and penetrations are the other weak points, because that is where the membrane has to turn corners and seal against other materials. Long-term ponding also works on the asphalt over time.
On single-ply, the failures are a bad weld, a puncture, and a flashing that pulled loose. A weld run too fast or too cool looks fine on the day and opens later under thermal movement, which is exactly why probing every seam matters. A dropped tool or a dragged piece of equipment can punch through a single sheet where two asphalt plies would have taken the hit. The part owners rarely budget for is the detailing and the ongoing inspection. A roof lives or dies at the flashings, and the annual walk that catches a lifted lap or a suspect weld early is far cheaper than the interior repair after water tracks into a suite.
Substrate, insulation, and getting the assembly right
The membrane is the top of a stack, and the layers under it decide how the roof performs. On a re-roof the crew has to know the deck (concrete, steel, or wood), the insulation type and whether it is dry, the vapour control, and the slope. Wet insulation left in place under a new membrane keeps the assembly damp, invites rot, and voids most warranties. Tapered insulation is how many roofs get their slope corrected so water actually reaches the drains.
Attachment has to match the deck and the wind exposure. Mechanically fastened single-ply relies on the fasteners and plates holding through wind uplift, while a fully adhered system relies on the bond. Torch-on relies on the base sheet attachment and the ply bond. A correct specification names the membrane and thickness, the insulation and its R-value target, the attachment method, the vapour control, and every flashing detail. If the proposal is one line that says new roof, the assembly has not been thought through.
Standards, testing, and what to verify in BC
You do not have to memorize standard numbers, but you should know they exist and ask that the work meet them. In British Columbia, RCABC, the Roofing Contractors Association of British Columbia, publishes roofing practice standards that cover SBS torch-on, TPO, and PVC assemblies, and it runs the RoofStar guarantee program for work installed to those standards by registered contractors. National material standards from CSA and CAN/CGSB cover the membranes and their components. ULC lists fire classifications for roofing assemblies, which is where roof fire ratings come from.
What to verify: that the system being quoted is an accepted assembly the contractor is registered to install, that the membrane and thickness are named, that the fire rating suits your building, and that the crew will probe single-ply welds or roll torch-on laps to confirm the bond. Do not accept invented clause numbers or vague claims of code compliance. Ask which standard and which guarantee, and confirm it with the association if the roof is a large investment. A serious contractor will welcome the question.
Where the cost actually comes from
Cost on either system is driven by the same handful of things, and none of them is the membrane name on the invoice. Roof access is a big one: getting crew, tear-off debris, and new material up and down a high-rise is a different job than a two-storey commercial roof with easy access. Tear-off and disposal of the old roof, the condition of the deck once you open it up, insulation and tapered systems to fix drainage, and the amount of detailing around parapets, drains, and rooftop equipment all move the number more than TPO versus mod-bit does.
The torch-on hot-work requirements add cost too: the protection sheets, the fire watch, and the coordination on an occupied building are real line items, not afterthoughts. Single-ply cost swings with membrane thickness and whether it is fastened or fully adhered. Rather than chase a price off a comparison chart, get a roof assessment that measures the area, checks the deck and drainage, and prices the detailing your specific roof needs. That is the only number that means anything, and it is the starting point for any building envelope repair we take on.
Lifecycle cost, not just the install price
The cheapest roof to install is rarely the cheapest roof to own. Both systems land in a similar service-life range, so the real lifecycle question is what you spend keeping the roof going and what the failure looks like when it comes. A roof that gets an annual inspection, has its drains cleared, and gets small repairs at the first sign of a lifted lap or a suspect weld will reach the top of its range. A roof left alone until a suite leaks will not, and the interior repair often costs more than years of maintenance would have.
Redundancy plays into this. A 2-ply torch-on roof gives you a second layer of margin, which can buy time on a roof that is hard to inspect or hard to keep people off. A single-ply roof has less margin, so the inspection and quick-repair discipline matters more. Neither is a set-and-forget roof. Budget for the maintenance up front, in the depreciation report and the annual plan, so the roof reaches the life you paid for. This is the same lifecycle thinking behind a full building restoration, where the cheapest first move is often the most expensive over twenty years.
Warranty reality: material, workmanship, and the guarantee
There are usually two or three layers of coverage, and they are not the same thing. The material warranty comes from the membrane maker and covers the membrane against manufacturing defects. It does not cover bad installation. The workmanship warranty comes from the roofer and covers their labour, which is only as good as the company still being in business when you need it. On single-ply, manufacturers often offer a longer NDL (no dollar limit) warranty, but only when a manufacturer-approved installer does the work to spec, so the installer\'s status matters.
The third layer, in BC, is the RCABC RoofStar guarantee, which is backed by the association rather than by one company. When a RoofStar-registered contractor installs an accepted SBS, TPO, or PVC assembly to the standard, the guarantee covers the roof even if that contractor later closes down, which a plain workmanship warranty cannot promise. For a strata this is real protection, because it does not depend on one firm surviving fifteen years. Read what each layer covers and excludes, and confirm the contractor is registered to provide the guarantee they are quoting.
Where each is the wrong tool
Torch-on is the wrong tool over an occupied combustible deck where the open flame cannot be safely managed, on a roof that ponds badly with no plan to fix drainage, and any time the crew cannot describe a hot-work and fire-watch plan. It is also a poor fit for a cold, wet install window with a tight schedule, because the asphalt bond fights the weather.
Single-ply is the wrong tool on a roof that takes heavy foot traffic and dropped tools where a single sheet keeps getting punctured, and anywhere the crew cannot show sound, probed welds. It is also the wrong call if the real problem is drainage and the plan is to lay a reflective sheet over the same low spots and call it done. In both cases the failure is not the membrane, it is using it where it does not belong, or skipping the prep that either system needs.
How to read a roofing proposal
A good roofing proposal reads like a specification, not a sales sheet. It names the deck and confirms its construction. It names the membrane, the maker, the thickness, and the attachment method. It spells out the insulation, the vapour control, and any tapered system to correct slope. It lists the flashing details at parapets, drains, and penetrations, and it says how the work will be checked, whether that is probing welds or rolling laps. For torch-on it includes the hot-work and fire-watch plan. It states the warranties and the guarantee, and it allows for what happens if the deck or insulation is found wet.
A weak proposal is a single line and a price. If two bids are far apart, the gap is almost always in the scope: one included tear-off, deck repair allowance, tapered insulation, and full detailing, and the other assumed the roof underneath is fine and priced a recover. Compare scopes, not just totals. When a strata puts these questions to every bidder, the differences between a careful contractor and a cheap one show up fast. Two sibling guides help here: our comparison of roof recover versus tear-off and, for wall assemblies, rainscreen versus face-sealed. For the full set, see the building envelope resource hub.
Four Metro Vancouver roofs and the honest call
The membrane that is right depends on the building in front of you. Here are four common cases and the reason behind each recommendation.
Occupied wood-frame strata, North Shore, four storeys
SituationA 1990s wood-frame condo with residents in every suite and a low-slope roof over the top floor. The deck is combustible. The roof is at end of life and the strata wants a replacement without moving anyone out.
The callSingle-ply (TPO or PVC), mechanically fastened or adhered, hot-air welded.
WhyThe deck is wood and the building is occupied, which is the exact case where an open torch is hard to justify. A smouldering fire on a combustible deck over occupied suites is the risk you cannot buy back. Hot-air welding removes the flame. A white reflective single-ply also cuts summer heat into the top floor, which is a common complaint in wood-frame buildings with thin roof assemblies.
Concrete-deck warehouse, Burnaby, light foot traffic
SituationA single-storey commercial warehouse with a large flat concrete roof, a handful of vents, and mechanical units serviced a few times a year. The roof ponds in two low spots after heavy rain.
The callSingle-ply PVC, with the low spots corrected by tapered insulation.
WhyThe known ponding points at PVC, which sits in standing water better than mod-bit over the long term. The reflective surface helps on a big open roof that bakes in summer. The concrete deck means torch-on would also be defensible on fire grounds, but with ponding in the picture the plastic membrane is the lower-worry call. Either way, fixing the slope in the two low spots matters more than the membrane name.
Concrete high-rise amenity roof, downtown Vancouver, heavy use
SituationA concrete-deck roof over a mechanical penthouse that crews walk constantly, with pavers, equipment, and regular service traffic. Non-combustible deck, good drainage, and the strata can accommodate a managed hot-work window.
The callTorch-on SBS 2-ply, with a full hot-work plan and fire watch.
WhyThis is where the honest answer favours torch-on. The deck is concrete, so the fire risk can be controlled with a protection sheet, extinguishers, and a fire watch after the torches shut off. The roof takes constant foot traffic and dropped tools, and two thick asphalt plies handle that abuse far better than a single sheet. The 2-ply redundancy is worth having on a roof this hard to keep people off. The choice here is driven by use and durability, not by fear of the flame, because the flame can be managed on this deck.
Small roof, many penetrations, mid-rise mixed-use
SituationA compact low-slope roof crowded with plumbing stacks, exhaust fans, a skylight curb, and two drains. Concrete deck, occupied units below, tight access.
The callSingle-ply, welded, by a crew that can show clean penetration details.
WhyOn a small roof the field membrane barely matters. Almost the whole roof is detail work around penetrations, and that is where both systems fail first. Single-ply keeps the open flame off an occupied building in a crowded, hard-to-watch space. The deciding question is not TPO versus mod-bit, it is which crew details a pipe boot and a curb cleanly. Ask to see photos of their flashing work on a similar roof before you sign.
Decision framework: ten questions that point to the right membrane
| Question | Lean toward | Reason |
|---|---|---|
| Building occupied during the work? | Lean single-ply | Torch-on brings an open flame and a smouldering-fire risk onto an occupied strata or commercial roof. Hot-air welded single-ply removes the flame, which is one less thing to manage over residents' heads. |
| Combustible deck or timber structure? | Strongly lean single-ply | A torch against a combustible deck is where hidden smouldering fires start. If the deck is wood or the assembly holds combustible material, taking the flame off the roof is the safer path. |
| Regular foot traffic or rooftop equipment service? | Lean torch-on | Two asphalt plies resist punctures from foot traffic, carts, and dropped tools far better than a single sheet. Mechanical penthouses and roofs walked often benefit from the extra armour. |
| Ponding water is a known problem? | Lean single-ply | Single-ply, PVC especially, is built to sit in standing water. Multi-ply mod-bit is more sensitive to long-term ponding, so on a flat roof with poor drainage the plastic membrane holds up better while you fix the slope. |
| Summer heat gain into top-floor units? | Lean single-ply (or reflective cap) | TPO and PVC are usually light and reflective, so they keep the roof surface cooler. A dark mod-bit roof runs hotter unless you add a reflective cap sheet or coating. |
| Want redundancy from more than one layer? | Lean torch-on | A 2-ply system does not depend on a single membrane holding out. A defect in one ply is backed by the other, which some owners and consultants value on a roof that is hard to reach. |
| Many penetrations, curbs, and odd corners? | Either, weld quality decides | Both systems live or die at the details. Torch-on flashings and single-ply welds each need a skilled hand at every pipe, drain, and curb. Ask to see how the crew details a penetration before you pick. |
| Deck is non-combustible and torching is properly managed? | Either is defensible | On a concrete deck with a fireproof protection sheet, extinguishers, and a proper fire watch after torching stops, torch-on's risk is controlled. At that point the choice comes down to traffic, ponding, and heat. |
| Cold, wet season install window? | Slight lean single-ply | Torch-on asphalt has to reach bonding temperature, which is slower and fussier in cold, damp coastal weather. Single-ply welding is less weather-sensitive, though both want a dry deck and a workable forecast. |
| Existing roof is also mod-bit and sound underneath? | Lean torch-on for a match | Matching an existing asphalt system can simplify tie-ins and future repairs. If a tear-off is happening anyway, this weighs less and the other factors take over. |
Questions to ask before you approve the scope
Put these to every contractor bidding your roof. The red-flag answer tells you as much as the good one.
-
What is the deck made of, and have you confirmed it?
Red flagA contractor who guesses at the deck type instead of confirming it, or who dismisses the fire question on a combustible deck, has not thought the job through.
-
For torch-on, what is your hot-work and fire-watch plan?
Red flagNo mention of a protection sheet, extinguishers on the deck, or a fire watch that stays after torching stops is a serious red flag on any torch-on bid.
-
For single-ply, how do you check the welds, and what thickness membrane?
Red flagIf they cannot explain probing the seams or will not commit to a membrane thickness and maker, the weld quality is a coin toss.
-
How will you fix the drainage and ponding, not just cover it?
Red flagA bid that lays new membrane over the same low spots without tapered insulation or slope correction is setting you up to be back on the roof early.
-
What warranty do I get, and who stands behind it?
Red flagVague talk of a warranty with no split between material and workmanship, or no mention of an RCABC RoofStar guarantee where one applies, means the coverage may be thinner than it sounds.
-
Are you registered to install this system for the warranty you are quoting?
Red flagManufacturer NDL warranties and RoofStar guarantees require an approved or registered installer. If they are not, the warranty may not exist.
-
How will you detail the parapets, drains, and penetrations?
Red flagA crew that cannot describe or show photos of their flashing details is telling you the details will be improvised on the day.
-
What happens if you open the roof and the deck or insulation is wet?
Red flagNo allowance for deck repair or wet insulation replacement means a change order later, or worse, a new roof laid over rot.
-
How do you protect residents and coordinate access on an occupied building?
Red flagNo plan for notices, fumes, noise, and safe access on an occupied strata suggests they do not work on occupied buildings often.
Quick answers
Is torch-on roofing a real fire risk on an occupied strata building?
Yes, and it is worth taking seriously. Torch-on is hot work: a propane torch with an open flame melts the underside of the membrane so it welds to the layer below. The specific danger is a smouldering fire that starts under the membrane, in a combustible deck or in trapped dust and debris, and does not show itself right away. It can flare up hours after the crew packs up, sometimes overnight. This is why a legitimate torch-on crew uses a fireproof base or protection sheet, keeps extinguishers on the deck, and holds a fire watch on site after the torches go off. On an occupied Vancouver or Burnaby strata tower with residents below, many owners and consultants prefer hot-air welded single-ply precisely because it takes the open flame out of the picture.
Do single-ply roof seams hold up as well as torch-on seams?
They hold up very well. TPO and PVC seams are joined with hot air: the welder heats two overlapping sheets and rolls them together so the plastic fuses into one continuous piece. A correctly made weld can be as strong as the membrane sheet on either side of it, so the seam is not the weak point people sometimes assume it is. The catch is that weld quality depends entirely on the installer getting the heat, speed, and roller pressure right, and on probing the finished welds to confirm they are continuous. A torch-on 2-ply system staggers the laps across two layers, which gives a different kind of security. Both approaches produce a reliable roof when the crew knows what they are doing, and both fail early when the seam work is rushed.
Which membrane lasts longer on a Vancouver low-slope roof, torch-on or single-ply?
On service life alone the two are close. A 2-ply torch-on SBS system typically lasts about 15 to 25 years on a Metro Vancouver roof when it is detailed and maintained well. TPO and PVC single-ply typically land in the same 15 to 25 year range when the welds are sound and the membrane is the right thickness, with PVC often reaching past 20 years. Neither wins on lifespan by a wide margin, so the real decision comes down to the other factors: fire risk during install, how much foot traffic the roof sees, whether the roof ponds, and whether you want a reflective surface. Detailing at the parapets, drains, and penetrations, plus a maintenance program, matters more to how long either roof lasts than the choice of membrane type.
Low-slope roof membrane questions
Is torch-on roofing a real fire risk on an occupied strata building?
Yes, and it is worth taking seriously. Torch-on is hot work: a propane torch with an open flame melts the underside of the membrane so it welds to the layer below. The specific danger is a smouldering fire that starts under the membrane, in a combustible deck or in trapped dust and debris, and does not show itself right away. It can flare up hours after the crew packs up, sometimes overnight. This is why a legitimate torch-on crew uses a fireproof base or protection sheet, keeps extinguishers on the deck, and holds a fire watch on site after the torches go off. On an occupied Vancouver or Burnaby strata tower with residents below, many owners and consultants prefer hot-air welded single-ply precisely because it takes the open flame out of the picture.
Do single-ply roof seams hold up as well as torch-on seams?
They hold up very well. TPO and PVC seams are joined with hot air: the welder heats two overlapping sheets and rolls them together so the plastic fuses into one continuous piece. A correctly made weld can be as strong as the membrane sheet on either side of it, so the seam is not the weak point people sometimes assume it is. The catch is that weld quality depends entirely on the installer getting the heat, speed, and roller pressure right, and on probing the finished welds to confirm they are continuous. A torch-on 2-ply system staggers the laps across two layers, which gives a different kind of security. Both approaches produce a reliable roof when the crew knows what they are doing, and both fail early when the seam work is rushed.
Which membrane lasts longer on a Vancouver low-slope roof, torch-on or single-ply?
On service life alone the two are close. A 2-ply torch-on SBS system typically lasts about 15 to 25 years on a Metro Vancouver roof when it is detailed and maintained well. TPO and PVC single-ply typically land in the same 15 to 25 year range when the welds are sound and the membrane is the right thickness, with PVC often reaching past 20 years. Neither wins on lifespan by a wide margin, so the real decision comes down to the other factors: fire risk during install, how much foot traffic the roof sees, whether the roof ponds, and whether you want a reflective surface. Detailing at the parapets, drains, and penetrations, plus a maintenance program, matters more to how long either roof lasts than the choice of membrane type.
Why does roof colour and reflectivity matter on a BC building?
A dark roof absorbs solar heat and runs hot in summer sun, which pushes heat into the top-floor units and drives up cooling load. TPO and PVC single-ply membranes are usually white or light grey, so they reflect a large share of that solar energy and keep the roof surface cooler. Torch-on mod-bit is dark by default, black or dark grey, unless you add a reflective granulated cap sheet or a reflective coating on top. On a Metro Vancouver roof the summer heat gain is not as punishing as it is in the interior of the province, but it still shows up as warmer top-floor suites and higher air-conditioning bills. If keeping the surface cool matters to your building, single-ply gives you that reflectivity out of the box, while mod-bit needs an added reflective layer to get there.
Can single-ply handle ponding water better than torch-on?
Generally yes. Single-ply membranes, and PVC in particular, are designed to sit in standing water without breaking down over time. Multi-ply modified bitumen is more sensitive to long-term ponding: water that sits for weeks works on the asphalt and the laps in a way it does not on a plastic sheet. On a Metro Vancouver low-slope roof that does not drain well, and given the coast sees well over 1,100 mm of rain a year, ponding is a common real-world problem rather than a theoretical one. If the roof has known low spots and standing water, single-ply is usually the safer membrane. The better long-term fix is to correct the slope and drainage so the roof sheds water regardless of which membrane sits on top, and any decent roof assessment should flag drainage first.
What safety steps should a torch-on crew follow in BC?
WorkSafeBC treats torch-on as hot work, and a proper crew treats it that way too. Before any flame goes on, they clear and protect combustible material, lay down a fireproof base or protection sheet over vulnerable areas of the deck, and keep charged fire extinguishers within reach on the roof. During the work the torch operator watches for smoke or scorching where the flame meets the deck. The step people forget is the fire watch: someone stays on the roof after torching stops, walking the area and checking for heat and smoke, because a smouldering fire can take hours to show. On an occupied building this also means coordinating with the strata so residents and the building manager know hot work is happening. If a contractor cannot explain their hot-work and fire-watch plan, that is a red flag on a torch-on job.
Should our strata pick torch-on or single-ply for our roof replacement?
It depends on the roof, not on which product is better in the abstract. Start with the deck: if it is combustible, the open-flame risk of torch-on pushes hard toward single-ply. Then look at how the roof is used. A roof with heavy foot traffic or mechanical equipment being serviced regularly benefits from the puncture resistance of two asphalt plies. If the roof ponds, single-ply, PVC especially, handles standing water better. If summer heat into the top floor is a complaint, a reflective single-ply surface helps. Many occupied Vancouver and North Vancouver stratas end up leaning single-ply mainly to keep an open flame off an occupied building, but a non-combustible deck with a properly managed torch-on install and a good fire watch is also a sound choice. The right answer comes from a roof assessment that looks at your deck type, drainage, traffic, and condition, not from a catalogue.
What is an RCABC RoofStar guarantee, and does it matter?
RCABC is the Roofing Contractors Association of British Columbia. It publishes roofing practice standards for the province and runs the RoofStar guarantee, which is a third-party guarantee backed by the association rather than by the individual roofer. When a RoofStar-registered contractor installs an accepted assembly to the standard, the guarantee covers the roof even if that contractor later goes out of business, which a plain workmanship warranty does not. RoofStar accepts SBS torch-on, TPO, and PVC assemblies, so it is available for either path here. It matters because it gives a strata a backstop that does not depend on one company still being around in fifteen years. Ask any bidder whether the job will carry a RoofStar guarantee and confirm they are registered to provide it.
Is torch-on ever banned or restricted on Vancouver buildings?
It is not banned outright across the board, but plenty of building owners, insurers, and strata councils restrict or refuse open-flame torching on their roofs, especially over occupied combustible structures. The reason is the hot-work fire risk and the insurance exposure that comes with it. Some insurers add conditions or higher premiums for torch work, and some owners write it out of their tender to remove the question. WorkSafeBC hot-work rules apply either way. If your building or your insurer restricts torching, single-ply with hot-air welding is the practical way to re-roof without an open flame. Check your insurance and any strata rules before a torch-on bid gets far.
Which membrane is cheaper, torch-on or single-ply?
Neither wins on price by a clean margin, because the membrane name is a small part of the total. The big cost drivers are the same for both: roof access on a high-rise versus an easy low commercial roof, tear-off and disposal of the old system, the condition of the deck once it is opened, tapered insulation to fix drainage, and the amount of detailing around parapets, drains, and rooftop equipment. Torch-on adds the hot-work costs, the protection sheets, the fire watch, and the coordination on an occupied building, which are real line items. Single-ply can cost more or less depending on membrane thickness and whether it is fastened or fully adhered. Rather than compare a price off a chart, get a roof assessment that measures the area, checks the deck and drainage, and prices the detailing your specific roof needs.
Can I recover over my old roof, or do I need a full tear-off?
Sometimes you can recover, and sometimes you should not. If the existing roof is sound and dry underneath, a recover can save the cost and disruption of a tear-off. If the insulation is wet, the deck is damaged, or there are already two roofs stacked up, a tear-off is the honest call because covering wet or failing layers just buries the problem. This decision is a whole topic on its own, and it interacts with the membrane choice: a recover changes what can be torched or welded on top. We cover the tradeoffs in our guide to roof recover versus tear-off. Whatever the membrane, the layers underneath decide whether a recover is safe.
How do heat-welded single-ply seams get as strong as the membrane?
When a hot-air welder is set correctly, it heats the two overlapping sheets to the point where the plastic surfaces melt and flow together, then a roller presses them so they fuse into one continuous piece. Done right, the joined area is effectively the same material as the sheet, so pulling on a good weld tears the membrane before it tears the seam. That is why a correct TPO or PVC weld can be as strong as the membrane itself. The whole thing depends on the operator dialing in heat, travel speed, and roller pressure for that day's conditions, then probing the cooled seam with a tool to find any spot that did not fully weld. A rushed or too-cool weld looks fine but pulls apart under thermal movement, which is why probing every seam is not optional.
Find out whether torch-on or single-ply is right for your roof
We assess low-slope roofs across Vancouver, North Vancouver, West Vancouver, and Burnaby. We check deck type, drainage, ponding, traffic, and the detailing at drains and parapets, so your strata or building owner has the data to choose the right membrane and budget it accurately.