SBS and APP Bitumen Membranes: The Difference and How to Select
What a modified bitumen membrane actually is
Before the SBS and APP argument is worth having, it is worth being precise about the object under discussion. A modified bitumen membrane is not a coating, not a liquid system and not a bitumen paint. It is a prefabricated composite sheet, and every property on its data sheet comes from one of three components.
Five layers, made in one pass
A reinforced bitumen membrane — the generic name the European product standard uses — is a factory-made composite. Working from the top down it is normally five things: a top surfacing, a layer of modified bitumen compound, a reinforcement carrier, a second layer of compound beneath the carrier, and a bottom face. In manufacture the carrier runs continuously off a roll into a bath of hot compound where it is saturated and coated on both faces, passes through calibrating rollers that set the finished thickness, receives its surfacings while the compound is still fluid, is cooled through chill rollers or a water bath, and is then trimmed, wound into rolls and palletised.
Two sentences carry most of what a buyer needs from that description. The compound does the waterproofing. The carrier does the mechanics. Nearly every technical argument about membranes is really an argument about one or the other, and the most common procurement error — specifying a membrane by thickness and modifier alone — is a failure to ask about the second one at all.
The compound
The compound is bitumen with a polymer dissolved and dispersed into it, usually with mineral filler and sometimes with flame retardants or other additives. Neat bitumen on its own is a poor membrane material and always has been: it is brittle at low service temperatures and it flows at high ones, and the window between those two limits is narrow. Oxidising the bitumen widens the window a little by raising the softening point, which is why traditional bituminous felts were made with blown grades, but oxidation buys heat resistance at the cost of cold flexibility. Polymer modification is the step that widens the window at both ends at once, and that single fact is the entire commercial reason modified membranes displaced unmodified felts.
The base bitumen underneath the polymer matters more than it is given credit for. A modified compound is normally built on a relatively soft distillation-grade bitumen, because the polymer has to swell in the maltene fraction to disperse properly and to form a stable phase. A hard, heavily oxidised bitumen has had much of that fraction consumed and makes a poor host for SBS in particular. Oxidised grades still have their place in membrane manufacture — as saturants and coatings in traditional non-modified felts, in some compound blends, and above all as the hot mopping asphalt that bonds sheets in built-up and hot-applied systems — but they are not usually the base for a high-performance modified compound.
The carrier
The carrier, also called the reinforcement, is the fabric buried in the middle of the sheet. It carries every tensile load the membrane will ever see, it decides how far the sheet can stretch before it tears, it decides how the sheet resists a nail shank or a dropped tool, and it decides whether the sheet stays the size it was when it left the factory. Polyester and glass fibre are the two families in normal use, with composites of the two occupying the middle ground. This is dealt with in full further down the page, because it is the part of the specification that gets left out most often.
The top surfacing
The top surface has three jobs: protect the compound from ultraviolet light, contribute to the roof’s fire performance, and give the finished appearance. The common options are:
- Mineral granules — ceramic-coated mineral chippings rolled into the hot compound. The standard finish for an exposed cap sheet. The granules block ultraviolet light from reaching the compound and add mass and fire resistance. Granule retention is itself a tested property.
- Fine sand or talc — used on sheets that will be covered by another layer, by ballast, by paving or by insulation, and on sheets that are to be bonded to. Sand is a release agent as much as a surfacing: it stops the roll blocking to itself in the stack.
- Polyethylene film — used on base sheets, on underlayers and on sheets that will be overlaid. It burns off cleanly under a torch.
- Metal foil — aluminium or, occasionally, copper. Used where a bright reflective exposed finish is wanted, and on some flashing and vapour control products.
The underside
The bottom face is chosen to match the application method, and it is the fastest way to tell what a roll is meant for:
- A thin thermofusible polyethylene film is the standard torch-applied underside. The film is not there to protect anything in service; it is a temperature indicator. When the film melts and disappears under the flame, the compound beneath it is at welding temperature. An installer who has burned the film away long before the bitumen bead appears has been holding the torch in one place for too long.
- Sand or talc is the underside for sheets applied in hot mopping asphalt or in cold adhesive, where the bond is made by the applied material rather than by melting the sheet.
- A silicone release film covers the pressure-sensitive adhesive layer of a self-adhesive sheet and is peeled off as the roll is unwound.
Rolls, formats and layers
Membranes are supplied in rolls, and the commercial formats are conventional rather than standardised. One metre is the near-universal width. A 3 mm or 4 mm sheet is commonly supplied in ten-metre rolls covering ten square metres, while heavier mineral-surfaced cap sheets are often shorter, at seven and a half or eight metres, to keep the roll to a weight two people can handle on a roof. Nominal thicknesses of 2, 3, 4 and 5 mm are the usual range. These are market conventions, not requirements of any standard — what the standards require is that the length, width, straightness, thickness and mass per unit area actually be measured and declared, and it is the declared figures on the manufacturer’s documentation that govern.
Roofs are most often built in two layers: a base sheet and a cap sheet, with the laps of the second layer offset from those of the first so that no line through the system passes through two laps at once. Single-layer systems exist and work, but they place the entire waterproofing duty on one sheet and one set of laps, which raises the requirement on the carrier and on workmanship at every joint.
What it is not
A reinforced bitumen membrane is not a liquid-applied system, not a bituminous coating brushed onto a wall, and not the same thing as a traditional built-up roof of saturated felts bonded in successive moppings of hot asphalt — although modified sheets are routinely used as cap sheets on top of built-up construction, and hot mopping asphalt is one of the ways a modified sheet is bonded. Nor is it a substitute for design. A membrane cannot correct a roof without falls, a detail that ponds, or an outlet set above the surrounding surface. Membranes overwhelmingly fail at laps, upstands, terminations, penetrations and outlets, and almost never in the middle of an undisturbed field of sheet.
SBS and APP: an elastomer and a plastomer
This is the question the waterproofing market actually asks, and it has a clean answer followed by five honest qualifications. The clean answer first.
What the polymer is asked to do
Bitumen is viscoelastic. At low temperature it behaves as a brittle solid and cracks under strain; at high temperature it flows. A polymer is added to push the brittle point down, push the flow point up, or both, and to give the compound some capacity to recover from deformation rather than simply accepting it. SBS and APP are two different answers to that problem, and they are different in kind, not merely in degree.
SBS is an elastomer
SBS is styrene-butadiene-styrene, a block copolymer. Each molecule is a long rubbery polybutadiene middle section with a rigid polystyrene block at each end. At service temperature the polystyrene end blocks are below their glass transition and aggregate together into hard domains, while the butadiene mid-blocks stretch between them. The result is a physically crosslinked network — a rubber whose crosslinks are not chemical bonds but clusters of hard polymer. Heat the compound past the point where the styrene domains soften and the network releases, so the material can be mixed, pumped, extruded and later melted under a torch; cool it and the network reforms. That thermal reversibility is exactly why the material can be manufactured on a coating line and welded on a roof, and it is what distinguishes a thermoplastic elastomer from a vulcanised rubber.
At the loadings used in membrane compounds — commonly reported in the region of 10 to 15 percent by mass of the compound, which is substantially more than the 3 to 7 percent typical of paving-grade polymer modified bitumen, and reported here as industry practice rather than as a standard requirement — the polymer forms a continuous phase running through the bitumen rather than discrete particles suspended in it. The compound at that point behaves as a bitumen-swollen rubber, and that is the source of everything SBS is valued for:
- Elastic recovery. Strain applied and released is largely returned. A sheet bridging a crack that opens and closes with temperature is not permanently stretched a little more each cycle.
- Low-temperature flexibility. The polybutadiene mid-block has a very low glass transition temperature, so the compound stays bendable far below the point where the base bitumen alone would crack. This is the single property that most distinguishes SBS in the field.
- Fatigue tolerance. Repeated small movements — the daily thermal cycle of a deck, the deflection of a floor under live load, the working of a structural joint — are absorbed rather than accumulated.
The limitation is chemical and it is not negotiable. The butadiene backbone is unsaturated: it carries carbon-to-carbon double bonds, and those are precisely the sites that ultraviolet light and atmospheric oxygen attack. An SBS compound left bare on an exposed roof will embrittle. That is why exposed SBS cap sheets are granule surfaced or foil faced, and why a smooth-surfaced SBS sheet is a base sheet or a covered sheet and should not be specified as a permanently exposed finish.
APP is a plastomer
APP is atactic polypropylene: a low-crystallinity, largely amorphous polypropylene, historically recovered as a by-product of polypropylene manufacture. Many membranes sold today as APP are in fact made with amorphous poly-alpha-olefins or blends that include isotactic polypropylene, because the classic atactic by-product became scarce as polymerisation catalysts improved; the trade designation APP has stuck to the whole plastomer-modified family and is used that way throughout this page and in the ASTM specifications.
APP does not build an elastic network. It behaves as a compatible plastic phase that stiffens the bitumen and raises its softening point sharply. Deformation is accommodated by the compound flowing and staying where it is put, not by stretching and springing back. It needs a considerably higher loading than SBS to do its job — figures in the region of 25 to 30 percent by mass of the compound are commonly reported, again as industry practice rather than as any standard’s requirement. What that buys is:
- Heat resistance. A high compound softening point, typically in the 150 to 160 °C region on manufacturers’ data, against roughly 110 to 120 °C for a typical SBS compound. On a fully exposed dark roof in a hot climate, surface temperatures run far above shade air temperature, and flow resistance at those temperatures is a real design constraint, not a theoretical one.
- Ultraviolet tolerance. The polypropylene backbone is saturated. It has none of the reactive double bonds that make SBS vulnerable, so an APP compound degrades more slowly under exposure. Granule surfacing is still normal and still recommended on exposed work, but the consequence of a scuffed or bare patch is less severe.
- Torching behaviour. An APP compound becomes genuinely fluid at torching temperature and welds readily to itself. Installers who have worked with both often describe APP as more forgiving under the flame.
The limitation is the mirror image of the SBS one. Cold flexibility is where APP is weak. Standard APP sheets have commonly declared low-temperature flexibility in the region of 0 to −15 °C, and while modern polyolefin formulations reach the lower end of that band and below, the family sits above SBS on this property. Those are typical declared values from manufacturers, not limits set by any standard. And because there is no elastic recovery, cyclic movement across a crack or a joint has to be absorbed by the carrier alone.
The plain rule
SBS belongs where the building moves or the winter is cold. APP belongs where the roof runs hot. That sentence is correct, it is what the chemistry predicts, and it is the right starting point for any selection.
Now qualify it honestly
Rules of thumb earn their keep by being short. They mislead badly the moment they are treated as specifications. Five qualifications matter:
- Read the declared figure, not the acronym. Formulations have moved. An APP sheet built on modern amorphous polyolefins may declare a low-temperature flexibility well below the classic APP figure, and a lightly modified SBS compound at low polymer loading may declare a value no better than a good APP one. The letters on the label are a description of chemistry; the number on the Declaration of Performance or the ASTM data sheet is the property. Specify the number.
- SBS is used successfully in hot climates every day. Nothing about the chemistry bars it. What matters is whether the compound’s flow resistance exceeds the real peak surface temperature of the roof with an adequate margin, and whether the surfacing protects the compound from ultraviolet exposure. A granule-surfaced SBS cap sheet with a declared flow resistance comfortably above the roof’s peak temperature is a legitimate hot-climate specification; an unprotected smooth SBS sheet on an exposed roof is not, in any climate.
- The application method often decides before the modifier does. Where an open flame cannot be used — over a combustible deck, in a refurbishment with an occupied building beneath, on a site whose insurer prohibits hot work, near a parapet cavity nobody can inspect — the practical choice narrows to self-adhesive and cold-applied systems, and those are almost exclusively SBS. This constraint overrides the climate argument more often than climate overrides it.
- The carrier can matter more than the modifier. An APP sheet on a heavy polyester carrier will accommodate more substrate movement than an SBS sheet on a glass fleece, because the movement capacity of a membrane is dominated by how far its reinforcement can stretch. If your problem is a cracking substrate, the carrier is the first thing to fix.
- Regional practice and installer competence are not trivia. APP dominates in southern Europe, the Middle East and much of Asia; SBS dominates in northern Europe and North America. Local supply, local detailing habits and the material a crew installs correctly every day of the year frequently produce a better roof than the theoretically superior product they have handled twice. Specify against what can actually be installed well on the site in question.
One last piece of perspective. Both are bitumen membranes, made on the same kind of line, with the same kinds of carrier, applied by the same trades. The differences set out on this page are real and they decide selection, but they are differences within one material family, not a contest between two technologies. Most roofs that fail do so because of a detail, a lap or a substrate, not because the wrong polymer was in the compound.
SBS versus APP, attribute by attribute
The full comparison in one place. Values described as typical are figures commonly declared by manufacturers and reported here as market practice; neither EN 13707 nor the ASTM specifications sets a single required softening point or cold flexibility for "SBS" or "APP" as such. Always work from the declared value for the specific sheet.
| Attribute | SBS modified | APP modified |
|---|---|---|
| Polymer class | Elastomer — a thermoplastic elastomer | Plastomer — an amorphous thermoplastic |
| Polymer | Styrene-butadiene-styrene block copolymer | Atactic polypropylene, or in modern practice amorphous poly-alpha-olefins and polypropylene blends sold under the same designation |
| Structure in the compound | Rigid polystyrene end-block domains physically crosslink rubbery butadiene mid-blocks, forming a continuous elastic network through the bitumen | A compatible amorphous plastic phase that stiffens the bitumen and raises its softening point; no elastic network is formed |
| Typical loading in the compound | In the region of 10–15 percent by mass (industry practice, not a standard requirement) | In the region of 25–30 percent by mass (industry practice, not a standard requirement) |
| Typical compound softening point | About 110–120 °C, ring and ball (EN 1427 / ASTM D36). Typical declared range, not a specification limit | About 150–160 °C, ring and ball (EN 1427 / ASTM D36). Typical declared range, not a specification limit |
| Typical declared cold flexibility | Commonly −15 to −25 °C to EN 1109, with high-performance grades declaring lower | Commonly 0 to −15 °C to EN 1109, with modern polyolefin formulations at the lower end |
| Elastic recovery | Yes. Strain is largely returned when the load is released | Essentially none. Deformation is largely permanent |
| Behaviour over a moving crack or joint | The compound stretches and recovers with the movement cycle | Movement is carried by the carrier alone; the compound does not spring back |
| Ultraviolet resistance of the compound | Lower. The unsaturated butadiene backbone is attacked by ultraviolet light and oxygen. Exposed sheets must be granule surfaced or foil faced | Higher. The saturated polypropylene backbone has no double bonds to attack. Granule surfacing is still normal on exposed work |
| Heat and flow resistance | Good, and set by the compound formulation. Verify the declared flow resistance against the roof’s real peak surface temperature | Better. This is the property APP exists for, and it is the reason it dominates in hot, fully exposed applications |
| Fatigue and movement tolerance | The strength of the material. Repeated small movements are absorbed rather than accumulated | Lower. Repeated movement is taken up by the reinforcement |
| Torch applied | Yes, commonly | Yes — this is the normal and usually the only method |
| Hot bitumen mopping | Yes. SBS sheets are routinely bonded in hot oxidised mopping asphalt where the manufacturer permits it | Not normally. APP sheets are not generally formulated for hot mopping; treat any such use as requiring explicit written approval from the sheet manufacturer |
| Cold adhesive | Yes, widely available | Limited, and manufacturer specific |
| Self-adhesive sheets | Yes. Effectively all self-adhesive bituminous sheets are SBS based | No. The compound is too stiff at ambient temperature to give a pressure-sensitive bond |
| ASTM product specifications | D6162 (polyester and glass combination), D6163 (glass fibre), D6164 (polyester) | D6222 (polyester), D6223 (polyester and glass combination) |
| European product standard | EN 13707 for roof waterproofing, which is modifier-neutral and covers both | EN 13707 for roof waterproofing, which is modifier-neutral and covers both |
| Where it belongs | Cold and temperate climates, moving or cracking substrates, structural and movement joints, decks with deflection, below-grade and buried work, and any project where flame is prohibited | Hot climates, fully exposed roofs with high ultraviolet load, sloped roofs where flow resistance governs, and projects where torch application is the established local method |
| Main limitation to design around | Ultraviolet degradation of an unprotected compound, and a lower softening point that has to be checked against peak roof surface temperature | Cold cracking, and no elastic recovery over cyclic movement. Also a narrower set of application options |
| Regional prevalence | Northern Europe and North America | Southern Europe, the Middle East and much of Asia |
The reinforcement, which decides more than the buyer thinks
The modifier gets the argument. The carrier gets left off the enquiry. Yet the carrier sets tensile strength, elongation, tear resistance, puncture resistance and dimensional stability — that is to say, almost everything on the mechanical half of the data sheet.
Here is the sentence to hold on to: the modifier decides how the sheet behaves with temperature, and the carrier decides how it behaves under load. Cold flexibility, flow resistance and ultraviolet durability belong to the compound. Tensile force, elongation, tear resistance, resistance to static loading and impact, and dimensional stability belong mainly to the carrier. A specification that names the polymer and the thickness but not the reinforcement has left out half the product.
Polyester nonwoven
Spunbond continuous-filament polyester, thermally bonded or needle-punched into a nonwoven mat, is the high-performance carrier. Carrier masses in the region of 150 to 250 g/m² are usual in membrane practice, with heavier grades in specialist sheets; those are typical manufacturing figures rather than requirements of any standard.
What polyester gives is elongation. A polyester-reinforced sheet commonly declares elongation at maximum tensile force somewhere in the region of 40 to 60 percent to EN 12311-1, against a few percent for a glass fleece sheet. It also gives high tensile force, excellent tear resistance at a nail shank or a fastener, good puncture resistance and good fatigue behaviour under repeated strain. That combination is why polyester is the carrier for anything that moves.
Where it belongs: over substrates that crack or move, across structural and movement joints, on decks with real deflection, on inverted and ballasted roofs and under paving or a green roof build-up where puncture is the governing risk, on car park decks, and in single-layer systems where one sheet carries the whole duty. It is also the carrier of choice in below-grade tanking, where the membrane has to bridge settlement cracks it will never be able to see again.
What you give up: polyester needs more heat to torch properly than a glass sheet of the same thickness, and it is dimensionally more mobile — polyester moves more with temperature and moisture than glass does. That last point is precisely why composite carriers were developed.
Glass fibre mat
Nonwoven glass fibre fleece, at carrier masses commonly around 50 to 60 g/m², is the stability carrier. Elongation is low — a few percent, commonly quoted in the 2 to 4 percent region — and that is not a defect, it is the specification. A glass-reinforced sheet stays the size it was made. It shows very little dimensional change on heating, it resists high temperature well, it lies flat, and it holds a consistent thickness through the coating line.
Where it belongs: base sheets and underlayers, vapour control layers, sheets bonded fully to a stable substrate such as sound concrete or screed, sheets under a further layer that provides the movement capacity, and any application where shrinkage of the sheet would be the failure mode. Glass carriers are also common in the first layer of two-layer systems, with a polyester cap sheet above providing the elongation.
What you give up: toughness and movement capacity. A glass fleece does not accommodate movement, it tears more readily at fasteners and at upstand fixings, it punctures more easily under a dropped tool or a heel, and it will not bridge a crack that is going to open. Using a glass-reinforced sheet over a moving substrate is one of the standard ways to produce a membrane that splits in a straight line along a crack in the deck below it.
Composite carriers
Composites exist to get most of the polyester’s elongation and tear resistance together with most of the glass’s dimensional stability. The usual constructions are a polyester nonwoven with glass yarns or a glass scrim laid into it, or a genuine glass-and-polyester blended nonwoven. The glass component restrains dimensional change and stiffens the sheet in the machine direction; the polyester component carries the elongation and the tear resistance.
ASTM recognises this family explicitly, and the structure of the ASTM specifications is the clearest published statement that the industry treats the carrier as a first-order variable. There are three SBS specifications and two APP specifications, and they are divided by reinforcement, not by anything else: ASTM D6162 covers SBS sheets with a combination of polyester and glass fibre reinforcement, D6163 covers SBS with glass fibre, D6164 covers SBS with polyester, D6222 covers APP with polyester and D6223 covers APP with a polyester and glass fibre combination.
Glass fabric
Woven glass fabric, as distinct from a nonwoven fleece, gives much higher tensile force than a mat at similar mass, with elongation still low. It appears in specialist sheets, in some flashing products and in sheets intended for high mechanical demand where movement is not the issue. It is a minority carrier in mainstream roofing but worth recognising when it appears on a data sheet.
Organic and cellulose felts
Bitumen-saturated organic felt was the original carrier and is effectively obsolete in modified bitumen membranes. It rots, it absorbs water, and it has neither the strength of polyester nor the stability of glass. If a sheet offered to you names an organic felt reinforcement, treat that as a signal about the whole product rather than as a detail.
What this means when you buy
- Two sheets both described as "4 mm SBS torch-on" can differ substantially in tensile force and by an order of magnitude in elongation, entirely because of the carrier. That description specifies almost nothing.
- Write the carrier into the specification: the reinforcement type and, where it matters, the carrier mass. On an ASTM basis, name the specification number, because the number is the carrier: D6164 is polyester and D6163 is glass, and asking for "an SBS sheet to ASTM" leaves the reinforcement open.
- Match the carrier to the failure you are trying to prevent. Movement and cracking call for polyester. Shrinkage and dimensional change call for glass. Puncture under ballast, paving or traffic calls for polyester. A stable, fully bonded substrate under a further layer will accept glass.
- Do not read thickness as strength. Thickness tells you how much compound is present, which relates to waterproofing durability, granule embedment and torching tolerance. It tells you nothing about tensile capacity, which is a property of the fabric in the middle.
Carrier types compared
Carrier masses and elongation figures below are values commonly seen in manufacturing and on declared data, given as typical industry practice. They are not requirements of EN 13707 or of the ASTM specifications, which require the properties to be measured and declared rather than fixing the carrier construction.
| Carrier | Typical carrier mass | Elongation character | What it is good at | Where it fails | Typical use |
|---|---|---|---|---|---|
| Polyester nonwoven, spunbond | About 150–250 g/m² | High — finished sheets commonly declare 40–60 percent elongation at maximum force to EN 12311-1 | Tensile force, elongation, tear resistance at fasteners, puncture resistance, fatigue under repeated movement | Greater dimensional change with temperature and moisture than glass; needs more torch heat than a glass sheet of the same thickness | Cap sheets, single-layer systems, moving substrates, movement joints, decks with deflection, ballasted and inverted roofs, tanking |
| Glass fibre nonwoven fleece | About 50–60 g/m² | Low — commonly quoted in the 2–4 percent region | Dimensional stability, heat resistance, flat lay, consistent thickness, resistance to shrinkage at terminations | Brittle. Will not bridge a moving crack, tears at fixings, punctures under point loads | Base sheets, underlayers, vapour control layers, fully bonded sheets on stable substrates, the lower layer of two-layer systems |
| Composite: polyester with glass yarns or scrim | Varies with construction | Moderate to high, restrained in the direction of the glass | Most of polyester’s elongation and tear resistance with much of glass’s dimensional stability | A more complex construction than either single carrier; behaviour is directional and has to be read from the declared machine and cross-machine values | Cap sheets where both movement capacity and dimensional stability are needed; the family covered by ASTM D6162 for SBS and D6223 for APP |
| Composite: blended glass and polyester nonwoven | Varies with construction | Moderate | A single fabric giving intermediate behaviour without a laid-in scrim | Neither the elongation of a full polyester carrier nor the stability of a pure glass one | General-purpose cap and base sheets where a middle position is acceptable |
| Woven glass fabric | Varies with weave | Low | High tensile force for its mass, good dimensional stability, good heat resistance | Same brittleness as a glass fleece; low movement capacity | Specialist sheets, flashings, and applications with high mechanical demand but little movement |
| Bitumen-saturated organic felt | Historic constructions | Low and unreliable | Nothing that a modern carrier does not do better | Rots, absorbs water, low and variable strength. Effectively obsolete in modified bitumen sheets | Legacy built-up roofing only. Treat its appearance in a modern offer as a warning about the product as a whole |
Application methods, and which modifier suits which
How the sheet is bonded is a specification decision with as much weight as the choice of polymer, and on many projects it is decided first — by fire risk, by the deck, by the insurer or by the building being occupied. The methods below are the ones in general use.
| Method | How the bond is made | Which modifier it suits | Where it is chosen | Main constraint or risk |
|---|---|---|---|---|
| Torch applied | A propane torch melts the underside of the roll as it is unrolled, so the compound welds to the substrate and to the previous sheet at the laps. A visible bead of molten bitumen ahead of the roll is the installer’s indicator of correct heat | APP almost always; SBS routinely where the manufacturer’s instructions permit | The default method for exposed roofs on non-combustible decks, and the established method across most of the hot-climate market | Naked flame. Fire risk at upstands, parapets, cavities and combustible decks is the dominant hazard in the whole trade, and hot work permits and a post-work fire watch are normal insurer requirements |
| Hot bitumen mopping | The sheet is bedded into a mopping of hot oxidised roofing asphalt spread ahead of the roll | SBS. APP sheets are not normally formulated for it — treat any such use as requiring written approval from the sheet manufacturer | Built-up and hybrid systems, and re-roofing over existing built-up construction where a kettle is already on site | A kettle of hot bitumen at working temperature is a serious burn and fire hazard. Temperature control matters: heating past the manufacturer’s maximum degrades the bitumen and approaches its flash point |
| Cold adhesive | A bitumen-based adhesive, solvent borne or water borne, is spread by squeegee, roller or spray and the sheet is laid into it | SBS, mainly. Cold adhesive systems for APP are limited and manufacturer specific | Occupied buildings, combustible decks, refurbishment, and any site where hot work is prohibited or heavily restricted | Coverage rate and open time are set by the adhesive manufacturer, not by any standard. Solvent-borne adhesives are flammable and can be trapped under the sheet if the flash-off period is cut short |
| Self-adhesive | A pressure-sensitive adhesive layer on the underside, protected by a silicone release film that is peeled as the roll is unwound. Bond is made by roller pressure | SBS only. There is no practical APP equivalent, because the compound is too stiff at ambient temperature to be pressure sensitive | Flame-free work, small areas, detailing, vapour control layers, tanking, and work by trades who are not specialist torch operators | Temperature dependent. Minimum ambient and substrate temperatures apply and are commonly stated in the region of 5 °C and rising, though the binding figure is always the manufacturer’s. Almost all substrates need priming, and pressure has to be applied by roller across the whole area, not just at the laps |
| Mechanically fastened | A base sheet is fastened through to the deck on a designed fastener pattern, and the cap sheet is then torched or bonded over it so the fasteners are covered | Both, according to the cap sheet chosen | Lightweight and profiled metal decks, and roofs where wind uplift governs and full adhesion is not practical | The fastener pattern is a wind uplift calculation, not a rule of thumb, and it is the roof’s weakest point. Tear resistance at the fastener is a carrier property, which pushes the specification towards polyester |
| Hot air welded laps | A hot air gun and roller weld the lap without a flame | Both, where the manufacturer’s system provides for it | Detailing and lap work where flame is restricted, and repairs | Slower than torching and highly dependent on operator skill and on consistent temperature and pressure |
| Loose laid and ballasted | The sheet is not bonded to the deck. Laps are welded, and the system is held down by ballast, paving or a green roof build-up | Both, but the puncture and static load demands push the specification towards polyester carriers | Inverted roofs, ballasted flat roofs, podium and plaza decks, green roofs | Water can track laterally under an unbonded sheet, so a leak is hard to trace to its entry point. Ballast weight and puncture resistance under the build-up are design inputs, and root resistance is a separate declared property for green roofs |
Application practice, and the safety that goes with it
Membranes overwhelmingly fail at laps, upstands, penetrations and terminations rather than in the field. Almost every one of those failures is an application failure, and several of the ways they happen also carry a genuine risk of fire or serious injury.
Torching, and the four ways it goes wrong
Torch application looks crude and is not. The objective is to bring the underside of the sheet and the surface it is landing on to welding temperature simultaneously, so that the two fuse into one mass of compound, and to do it while moving. The burn-off film on the underside is the temperature indicator, and a bead of molten bitumen squeezing out ahead of the roll, commonly described as roughly 10 to 15 mm of visible bitumen, is the working sign that the weld is being made. That bead figure is installer practice, not a standard requirement, and the manufacturer’s instructions govern.
- Too little heat. The film burns away, the roll goes down, and the sheet appears to be stuck. Nothing has welded. The bond fails under wind uplift or when the substrate first moves, and a lap that was never fused opens as a straight line of water entry. This is the commonest defect and it is invisible on the day.
- Too much heat, held in one place. The compound is degraded, the polymer is damaged, and on a polyester carrier the fabric itself can be scorched. The sheet then has a soft, over-cooked band with reduced strength running through it.
- Torching a cold roll. Rolls that have been stored outside in cold weather do not unroll flat and do not take heat evenly. Membrane is normally required to be stored upright, on end, under cover, and brought to a workable temperature before use.
- Torching details as if they were field sheet. Upstands, parapets, corners, outlets and pipe penetrations need cut and shaped pieces, patient work and often a hot air gun rather than a torch. They are where the flame is closest to a cavity, closest to timber, and least visible — and where roof fires start.
The fire risk is the defining hazard of the trade
Torch-applied roofing sets fire to buildings. The mechanism is nearly always the same: heat is applied at a junction — a parapet, an upstand, a verge, an eaves detail — and passes into a concealed void containing timber, insulation, birds’ nests or old felt. Nothing appears to be wrong. The fire develops slowly inside the void and is discovered hours later, often after the crew has left the site. The controls that address this are procedural rather than technical, and they are standard requirements of most insurers and hot work permit systems rather than requirements of any product standard:
- A hot work permit for the day, with the work area agreed and inspected before work starts.
- Combustible material removed from the work zone, and voids at upstands and parapets checked and, where necessary, closed or protected.
- Fire extinguishers at the working position, not at the hoist.
- A fire watch continuing after work stops, with the duration set by the permit system or the insurer. This is the control that catches the void fire, and it is the one most often skipped.
- Detailing at the most sensitive junctions designed out of torch application altogether, using self-adhesive or cold-applied products at parapets and around combustible construction.
- The torch equipment itself checked before it is lit: hoses inspected along their length for cuts and heat damage, connections leak-tested with soapy water rather than by ear, the regulator and hose check valve in place and working, and the propane cylinder kept upright, secured, and back from the working flame rather than dragged along beside it. A torch left burning and put down on a roll is a common ignition source in its own right.
Hot mopping asphalt: what the bitumen has to be
Where SBS sheets are bonded in hot bitumen, the mopping asphalt is an oxidised roofing grade. In North American practice it is specified to ASTM D312 / D312M, which defines four types by softening point measured by ASTM D36: Type I at 57 to 66 °C, Type II at 70 to 80 °C, Type III at 85 to 96 °C and Type IV at 99 to 107 °C. Types III and IV are the steep-slope grades, chosen so the bitumen does not run down a pitched roof in summer; Type I is a dead-level grade. D312 also requires a minimum flash point of 260 °C by Cleveland open cup (ASTM D92) and a high minimum solubility, which is what distinguishes a roofing asphalt from something that merely looks like one. These are the oxidised grades this site supplies.
Two working temperatures matter and they are not the same number. The equiviscous temperature is the temperature at which the bitumen has the viscosity needed to be spread and to wet the sheet properly; United States roofing-industry practice defines it as the temperature at which the material reaches a viscosity of 125 centipoise for mop application, or 75 centipoise for a mechanical spreader, and applies the material within a window commonly given as roughly ±14 °C (25 °F) of that figure. Those reference points are industry practice, not requirements of any material standard, and the equiviscous temperature is a property of the individual batch: it cannot be inferred from the grade name, and it belongs on the producer’s data sheet rather than in a general table. Separately, the kettle temperature is capped by the bitumen manufacturer’s stated maximum and by the finished blowing temperature of the grade, above which the blowing reaction begins to reverse and the softening point that was bought is quietly lost. ASTM D312 requires a minimum flash point of 260 °C, and the working ceiling this site publishes for oxidised grades is 230 °C — which leaves roughly thirty degrees of margin to that specification minimum, and a general oxidised export specification quoting a 250 °C minimum leaves only about twenty. Neither margin is generous, and a kettle nobody is watching has none at all. Neither the equiviscous temperature nor the kettle ceiling is a requirement of ASTM D312: the first is a batch property and the second is manufacturer instruction and site control. General grade-by-grade heating and storage windows are set out in the bitumen heating temperature guide.
A kettle is the most dangerous item on a roofing site. Hot bitumen at working temperature causes deep burns that continue to burn after contact because the material sticks to skin and cannot be removed. Never introduce anything containing water into hot bitumen — water flashes to steam instantly and throws the contents of the kettle out of the lid. Keep the kettle lid closed, keep it off the roof and away from the building where the layout allows, never leave it unattended while lit, and have the correct extinguisher for a flammable-liquid fire at the kettle itself rather than somewhere on the site. Never use water on a bitumen fire.
Protection for the person doing the work
The protection for hot bitumen and torch work is specific, and it is not the same as general site kit. Heat-resistant gauntlets worn loose enough to be shaken off in one movement rather than gloves that have to be pulled off; sleeves worn down and over the gauntlet cuff so that a splash cannot run inside; trouser legs worn outside the boots for the same reason; and eye and face protection whenever material is being charged, poured, mopped or torched. Work upwind of the kettle and the mop where the roof layout allows, because fume concentration is highest directly above hot open material, and keep the number of people standing over an open kettle to the ones who need to be there.
If hot bitumen reaches skin, cool it immediately with clean cold running water and keep cooling — on the way to hospital as well. Do not try to peel the hardened bitumen off and do not use solvent to remove it: it has bonded to the skin and taking it off takes the skin with it, which is work for a burns unit and not for the site first-aid box. Every material in this operation — the bitumen, the primer, the cold adhesive, the propane — has a Safety Data Sheet issued for that specific product, and the flash point, fume-exposure and first-aid sections of it are the ones to have read before the kettle is lit rather than after.
Priming, and why membranes lift off concrete
Almost every bond onto concrete, screed, masonry or metal needs a primer. A bituminous primer — specified in North American practice to ASTM D41 / D41M, the specification for asphalt primer used in roofing, dampproofing and waterproofing — penetrates the surface, binds residual dust and gives the membrane something to key into. Membranes that lift off concrete in sheets have usually been laid onto a surface that was dusty, damp, or still carrying a curing compound or release oil from the formwork. The primer must also be allowed to dry before the sheet goes on; a torch flame over wet solvent primer is both a bond failure and a fire.
Laps, and where the water actually gets in
Side and end laps are the membrane. Common practice puts side laps in the region of 80 to 100 mm and end or head laps in the region of 100 to 150 mm, with laps in successive layers offset from each other, but the binding figures are the manufacturer’s system instructions and the project specification, and they vary with the product, the layer and the slope. What does not vary is the checking: a lap is proved by the continuous bitumen bead squeezed out along its length, and by a probe run along the edge once the sheet has cooled. End laps, where the granule surface of the sheet beneath has to be heated and the granules bedded down before the next sheet lands, are the weakest point in any roof and deserve the most attention.
Self-adhesive and cold-applied work
Self-adhesive sheets fail for two reasons, both avoidable. The first is temperature: a pressure-sensitive adhesive that is too cold does not wet the substrate, and the sheet appears to be stuck while being held on by nothing. Minimum application temperatures are commonly quoted around 5 °C and rising, but the manufacturer’s figure for the specific product is the one that governs. The second is pressure: the bond is made by rolling, over the whole area and again along every lap, and a crew that rolls only the laps has bonded only the laps. Cold adhesives fail for a third reason of their own — solvent trapped under the sheet because the flash-off period was cut to keep the programme, producing blisters and a soft, uncured film at the interface.
The things that undo good work
- Laying onto a damp substrate. Trapped moisture becomes vapour under a dark roof in sunshine and lifts the sheet into blisters. Concrete and screed need to be dry, not merely dry on top.
- Working in rain, or with rain imminent. Water at a lap prevents the weld entirely.
- Detailing left to the end of the day. Upstands and outlets are the most demanding work on the roof and are routinely done last, quickly, by a tired crew.
- Foot and site traffic on a fresh membrane. Freshly laid compound is soft. Boards and a marked access route prevent punctures that are otherwise found later by the leak they cause.
- Storing rolls flat. Rolls stored on their side deform, and a deformed roll will not lay flat or unroll evenly. Store upright, under cover, off the ground.
The governing standards for reinforced bitumen sheets
Two systems govern this market and they work differently. The European system requires the manufacturer to measure a defined list of characteristics by named test methods and to declare the results, leaving the specifier to set the levels. The ASTM system sets minimum property limits by type and grade within specifications that are divided by modifier and by reinforcement. Both are named below with what each covers. Where a limit is not quoted here, it is because the value should be read from the current edition of the standard rather than from a web page.
| Standard | Subject | What it covers | What it does not do |
|---|---|---|---|
| EN 13707 | Flexible sheets for waterproofing — reinforced bitumen sheets for roof waterproofing: definitions and characteristics | The core European product standard for roofing membranes. It defines the product, lists the characteristics that must be determined and declared — watertightness, tensile properties, elongation, tear resistance, joint peel and shear strength, resistance to impact and static loading, flexibility at low temperature, flow resistance at elevated temperature, dimensional stability, reaction to fire, external fire performance, durability after ageing, and dimensions and mass — and names the EN test method for each. It is a harmonised standard supporting CE marking and a Declaration of Performance | It does not classify sheets as SBS or APP, and for most characteristics it does not set a single pass level. Two sheets can both conform to EN 13707 and be very different products. The performance levels are set by the specifier, the national annex or the project specification |
| EN 13969 | Flexible sheets for waterproofing — bitumen damp proof sheets including bitumen basement tanking sheets | The equivalent product standard for below-ground and damp-proofing applications rather than roofs | Same limitation: characteristics are declared, not graded into a single performance class |
| EN 13970 | Flexible sheets for waterproofing — bitumen water vapour control layers | Bituminous vapour control layers, where water vapour transmission is the defining property | Not a roof waterproofing standard |
| EN 13859-1 | Flexible sheets for waterproofing — underlays for discontinuous roofing | Underlay sheets beneath tiles, slates and similar discontinuous coverings | Does not cover the waterproofing layer of a flat roof |
| EN 14695 | Flexible sheets for waterproofing — reinforced bitumen sheets for waterproofing of concrete bridge decks and other trafficked concrete surfaces | The bridge deck and trafficked concrete application, where bond to concrete and behaviour under a hot asphalt surfacing govern | Not applicable to conventional roofing |
| ASTM D6164 / D6164M | SBS modified bituminous sheet materials using polyester reinforcements | The North American product specification for SBS sheets on a polyester carrier, setting minimum physical property requirements by type and by grade, with grades distinguishing smooth-surfaced from granule-surfaced sheets | Does not cover glass or composite reinforced SBS sheets — those are separate specifications |
| ASTM D6163 / D6163M | SBS modified bituminous sheet materials using glass fiber reinforcements | The same structure of requirements for SBS sheets on a glass fibre carrier | Does not cover polyester or composite carriers |
| ASTM D6162 / D6162M | SBS modified bituminous sheet materials using a combination of polyester and glass fiber reinforcements | SBS sheets on composite carriers | Does not cover single-material carriers |
| ASTM D6222 / D6222M | APP modified bituminous sheet materials using polyester reinforcements | The North American product specification for APP sheets on a polyester carrier, with the same type and grade structure | Does not cover composite reinforced APP sheets |
| ASTM D6223 / D6223M | APP modified bituminous sheet materials using a combination of polyester and glass fiber reinforcements | APP sheets on composite carriers | Does not cover polyester-only APP sheets |
| ASTM D5147 / D5147M | Sampling and testing modified bituminous sheet material | The test method document behind all five product specifications above. It covers sampling and the determination of thickness, mass, peak load and ultimate elongation, tear strength, low-temperature flexibility, dimensional stability, compound stability and granule embedment | It is a test method standard and sets no acceptance limits of its own. The limits live in D6162, D6163, D6164, D6222 and D6223 |
| ASTM D312 / D312M | Asphalt used in roofing | The oxidised roofing bitumen used as hot mopping asphalt, in four types by softening point to ASTM D36: Type I 57–66 °C, Type II 70–80 °C, Type III 85–96 °C, Type IV 99–107 °C, with a minimum flash point of 260 °C by ASTM D92 | It is a bitumen specification, not a membrane specification. It says nothing about the sheet |
| ASTM D41 / D41M | Asphalt primer used in roofing, dampproofing and waterproofing | The cutback bituminous primer applied to concrete, masonry and metal before the membrane | Does not cover cold adhesives or the membrane itself |
| ASTM D4601 / D4601M | Asphalt-coated glass fiber base sheet used in roofing | Glass fibre base sheets used beneath modified bitumen cap sheets in built-up and hybrid systems | Not a modified bitumen sheet specification |
| EN 13501-1 | Fire classification of construction products and building elements — reaction to fire | The European reaction-to-fire classification declared for the membrane as a product | Says nothing about the roof’s behaviour under fire from outside |
| EN 13501-5 with EN 1187 | External fire exposure to roofs — classification and test methods | The performance of the roof build-up when exposed to fire from outside, which is a system property rather than a sheet property | Cannot be transferred between build-ups. A classification belongs to the tested construction, not to the membrane alone |
| ASTM E108 | Fire tests of roof coverings | The North American external fire exposure test for roof coverings, reported as Class A, B or C | Also a system test. Read the tested build-up, not the sheet name |
What a membrane data sheet tells you, property by property
This is the table to keep beside a supplier’s technical data sheet or Declaration of Performance. Each line gives the property, the test method that produces it under both systems, and — the part that matters — what the number actually predicts about the roof. Properties are grouped so that compound properties and carrier properties can be told apart at a glance.
| Property | EN test method | ASTM test method | What it predicts in service | Belongs mainly to |
|---|---|---|---|---|
| Thickness and mass per unit area | EN 1849-1 | ASTM D5147 | How much compound is present, which governs waterproofing reserve, granule embedment and tolerance of imperfect torching. Not a measure of strength | The compound |
| Length, width and straightness | EN 1848-1 | ASTM D5147 | Whether the roll covers the area it is invoiced for, and whether it lays straight. A sheet that will not run straight produces laps that wander | The product |
| Softening point of the compound | EN 1427 | ASTM D36 | The classic indicator of heat resistance and the clearest single number separating an SBS compound from an APP one. Not a declared characteristic under EN 13707 but almost always on the manufacturer’s data sheet | The compound |
| Flexibility at low temperature | EN 1109 | ASTM D5147, low temperature flexibility | The temperature below which the sheet cracks when bent. It predicts winter installation limits and cold cracking in service, and it is the property on which SBS and APP most clearly diverge. In EN 1109 the specimen is bent over a mandrel of defined diameter at controlled temperature and the declared value is the lowest temperature at which no cracking occurs | The compound |
| Flow resistance at elevated temperature | EN 1110 | ASTM D5147, compound stability | Whether the compound stays where it was laid on a hot roof, on a slope, and at a lap. In EN 1110 specimens are held vertically in an oven and the declared value is the highest temperature at which slippage stays within the limit the standard sets. Compare it against the real peak surface temperature of a dark roof, which runs well above shade air temperature | The compound |
| Maximum tensile force, longitudinal and transverse | EN 12311-1 | ASTM D5147, peak load | The load the sheet can carry before it breaks, in each direction. It predicts survival of wind uplift, handling, thermal restraint and substrate strain. Always read both directions: reinforcements are directional | The carrier |
| Elongation at maximum tensile force | EN 12311-1 | ASTM D5147, ultimate elongation | How far the sheet can stretch before it fails, which is the single best indicator of whether it will bridge a crack or accommodate a moving joint. This is where polyester and glass carriers differ by an order of magnitude | The carrier |
| Resistance to tearing, nail shank | EN 12310-1 | ASTM D5147, tear strength | Whether the sheet tears out at a fastener or a fixing under wind uplift or thermal movement. Critical on mechanically fastened systems and at upstand fixings | The carrier |
| Dimensional stability | EN 1107-1 | ASTM D5147, dimensional stability | How much the sheet shrinks or grows on heating. Shrinkage is what opens laps, pulls sheets off upstands and tears a membrane at its terminations months after installation. This is the property glass carriers exist for | The carrier |
| Resistance to water penetration | EN 1928 | Not covered by ASTM D5147 | Whether the sheet itself is watertight under pressure. In EN 1928 a specimen is subjected to a defined water pressure for a defined period and examined for penetration, and the result is declared as a pass at the stated pressure | The compound and the sheet as made |
| Resistance to impact | EN 12691 | Not covered by ASTM D5147 | Puncture by a dropped tool, a stone or hail. It is declared as a drop height and it is tested on both hard and soft substrates, because the substrate changes the answer completely | The carrier, supported by compound thickness |
| Resistance to static loading | EN 12730 | Not covered by ASTM D5147 | Puncture under a sustained load rather than an impact: ballast, paving slabs, plant feet, a green roof build-up, maintenance traffic. The governing property on inverted and ballasted roofs | The carrier, supported by compound thickness |
| Joint peel and shear strength | EN 12316-1 and EN 12317-1 | Not covered by ASTM D5147 | How strong a correctly made lap is in peel and in shear. It matters because laps are where roofs leak, and because a specification that never tests laps is testing the wrong thing | The compound and the workmanship |
| Adhesion of granules | EN 12039 | ASTM D5147, granule embedment | How well the mineral surfacing stays attached. Granule loss exposes the compound to ultraviolet light, and on an SBS sheet that is the beginning of embrittlement | The compound and the surfacing |
| Durability — artificial ageing at elevated temperature | EN 1296, with properties retested afterwards | Not covered by ASTM D5147 | Whether the sheet keeps its low-temperature flexibility and its mechanical properties after long-term heat exposure. Retained flexibility after ageing is a far better durability indicator than the as-made value | The compound |
| Durability — artificial ageing under ultraviolet, heat and water | EN 1297, with properties retested afterwards | Not covered by ASTM D5147 | Weathering resistance of an exposed sheet. This is where the SBS and APP difference in ultraviolet tolerance shows up as a measured result rather than as chemistry | The compound and the surfacing |
| Water vapour transmission | EN 1931 | Not covered by ASTM D5147 | Vapour control performance, which is the whole point of a vapour control layer and a design input for the build-up above it | The compound and the sheet as made |
| Resistance to root penetration | EN 13948 | Not covered by ASTM D5147 | Whether the membrane survives a green roof. It is a separate declared property and it is not implied by any other line on the data sheet | The compound, usually with a root-inhibiting additive |
| Reaction to fire | EN 13501-1 | Not applicable | The classification of the product itself when exposed to fire | The product |
| External fire performance | EN 13501-5 with EN 1187 | ASTM E108 | The behaviour of the whole roof build-up under fire from outside. It is a system classification and cannot be transferred to a different build-up | The system, not the sheet |
Making the selection, and what this site actually supplies
The final section does two things: it reduces the whole page to the questions that decide a real specification, and it states plainly what part of this market this site is in.
Seven questions that settle the selection
- What is the lowest temperature the membrane will see, and what does the sheet declare to EN 1109? Put a margin between the two. A sheet declaring −5 °C on a roof that reaches −15 °C is a crack waiting for a cold morning, and installation in winter is limited by the same number.
- What is the highest surface temperature the roof will reach, and what does the sheet declare to EN 1110? Use the surface temperature of a dark roof in full sun, not the shade air temperature, and add the slope: flow resistance matters far more on a pitched or vertical surface than on a flat one.
- Does the substrate move? A deck that deflects, a substrate that cracks, a structural or movement joint, a lightweight deck under wind load. If the answer is yes, the carrier is polyester or a composite, and elastic recovery makes SBS the natural compound.
- Will the membrane be exposed, or covered? Exposed means granule surfaced, and it means the ultraviolet ageing result to EN 1297 matters. Covered by ballast, paving or a green roof build-up means resistance to static loading and impact matter more than ultraviolet performance, and root resistance becomes a separate requirement.
- Is a naked flame permitted on this site? This one question can decide the whole specification. If the answer is no, the practical route is self-adhesive or cold-applied, and that means SBS.
- What fire performance does the building require? External fire performance is a property of the tested build-up, not of the sheet, so the answer has to come from a classification for the actual construction: deck, insulation, adhesive and both membrane layers.
- What can the installing contractor do well? A correctly installed second-choice membrane outperforms a badly installed first-choice one every time. On most roofs, workmanship at laps, upstands and outlets has more influence on service life than the choice between two competent compounds.
How to write the enquiry so the answers are comparable
Specify by declared property, not by adjective. An enquiry that says "4 mm APP torch-on" will bring back offers that differ in carrier, in cold flexibility and in tensile capacity by amounts that make them incomparable. An enquiry that names the reinforcement type, the minimum declared tensile force in both directions, the minimum elongation, the maximum low-temperature flexibility value, the minimum flow resistance, the surfacing and the required fire classification will bring back offers that can be set beside each other. On an ASTM basis, quoting the specification number, the type and the grade does most of that work in a single line, because the specification number carries the reinforcement and the modifier with it.
What this site supplies
This site supplies bitumen. It does not manufacture or sell finished waterproofing membranes. There are no rolls, no torches, no adhesives, no primers and no granules in our scope, and nothing on this page is an offer of a membrane. That is worth saying plainly, because a page this long about membranes would otherwise imply otherwise.
What we do supply is the material membranes are made from and laid in:
- Oxidised bitumen in the blown grades used in membrane manufacture and as hot mopping asphalt. Oxidised grades are designated by softening point and penetration — 85/25, 90/15, 95/25, 115/15, 150/5 and the rest of the family — where the first figure is the ring and ball softening point and the second the penetration at 25 °C. Where a North American specification governs, the equivalent framework is ASTM D312 Types I to IV described in the standards table above.
- Polymer modified bitumen, for buyers compounding their own membrane material or specifying a modified binder for related work.
- Penetration-grade bitumen as the base for modified compounding, where a softer, maltene-rich base is needed for the polymer to disperse into.
- Industrial bitumen for the wider set of non-paving applications, including the enamel grades used in pipeline coating, which is a different product family from roofing membrane compound and should not be confused with it.
The neighbouring application pages on this site set out the same material from the other direction: roofing bitumen covers the grades and their selection for roofing work, and waterproofing bitumen covers waterproofing applications more broadly.
Where to buy the membrane itself
From a membrane manufacturer, and on documentation. In Europe that means a Declaration of Performance under the harmonised standard with the declared values for the characteristics your specification names. In North America it means a technical data sheet stating conformity to the applicable ASTM specification, with the type and grade. In both cases ask for the document for the product being supplied rather than a general brochure, check that the reinforcement named on the document is the one you specified, and check that the declared low-temperature flexibility and flow resistance figures still hold after ageing. A supplier who cannot produce that paperwork for the specific product is not a supplier you can hold to anything.
Our own supply is quoted the same way, against the specification you send. Middle East origin bitumen is offered with a Certificate of Analysis for the batch, and the grade, test methods and packing are confirmed in writing before shipment rather than described in general terms.
Frequently asked questions about SBS and APP membranes
What is the difference between SBS and APP bitumen membranes?
SBS is styrene-butadiene-styrene, an elastomeric block copolymer that forms a physically crosslinked rubber network in the bitumen. It gives the compound elastic recovery and good low-temperature flexibility, with typical declared cold flexibility around −15 to −25 °C and a compound softening point around 110 to 120 °C. APP is atactic polypropylene, a plastomeric modifier that stiffens the bitumen and raises the softening point sharply, typically to around 150 to 160 °C, with better ultraviolet tolerance because its backbone is saturated, but with poorer cold flexibility and essentially no elastic recovery. In short: SBS belongs where the building moves or the winter is cold, APP where the roof runs hot and fully exposed. Those softening point and flexibility figures are typical declared values from manufacturers, not requirements of any standard.
Which is better, SBS or APP?
Neither, in the abstract. They are answers to different problems. Ask instead what the membrane has to survive. Cyclic movement, a cracking substrate or a cold winter points to SBS. High roof surface temperatures, steep slopes and heavy ultraviolet exposure point to APP. Then check the constraints that override both: if naked flame is prohibited on the site, the answer is SBS, because self-adhesive and cold-applied bituminous sheets are effectively all SBS based. And read the declared values rather than the acronym, because modern formulations overlap considerably at the edges.
Can APP membranes be applied with hot bitumen mopping?
Not as a general practice. APP sheets are formulated for torch application and are not normally designed to be bonded in hot oxidised mopping asphalt; SBS sheets are routinely applied both ways, torched or mopped, where the manufacturer’s instructions permit. If a project requires an APP sheet to be laid in hot bitumen, that is a question for the sheet manufacturer in writing, not a decision for the site. The general rule to work from is that APP is normally torched, and SBS can be torched, mopped, laid in cold adhesive or supplied self-adhesive.
Why does the reinforcement carrier matter as much as the polymer?
Because the compound and the carrier control different halves of the data sheet. The compound decides how the sheet behaves with temperature — cold flexibility, flow resistance, ultraviolet durability. The carrier decides how it behaves under load — tensile force, elongation, tear resistance at fasteners, puncture resistance and dimensional stability. Polyester carriers give high elongation, commonly declared in the region of 40 to 60 percent at maximum force when measured to EN 12311-1, along with good tear and puncture resistance. Glass fibre carriers give elongation of only a few percent but excellent dimensional stability. Those elongation figures are values typically declared by manufacturers, not levels required by EN 13707 or by the ASTM specifications, which require the property to be measured and declared rather than fixing a limit for the carrier. Two sheets both described as 4 mm SBS can therefore differ by an order of magnitude in how far they stretch before failing, entirely because of the fabric buried in the middle.
Should I specify a polyester or a glass fibre carrier?
Polyester where the substrate moves, cracks or deflects, where the membrane crosses a movement joint, where it will be punctured by ballast, paving, a green roof build-up or traffic, and in single-layer systems where one sheet carries the whole duty. Glass where dimensional stability is the requirement and movement is not expected: base sheets and underlayers, vapour control layers, and sheets fully bonded to a stable substrate beneath a second layer that provides the movement capacity. Composite carriers combining polyester and glass exist precisely to occupy the middle ground, and ASTM D6162 for SBS and D6223 for APP are the specifications that cover them.
What does EN 13707 actually require?
EN 13707 is the European product standard for reinforced bitumen sheets for roof waterproofing. It defines the product and requires the manufacturer to determine and declare a defined list of characteristics by named EN test methods: watertightness to EN 1928, tensile force and elongation to EN 12311-1, tear resistance to EN 12310-1, joint peel and shear to EN 12316-1 and EN 12317-1, impact to EN 12691, static loading to EN 12730, low-temperature flexibility to EN 1109, flow resistance to EN 1110, dimensional stability to EN 1107-1, ageing to EN 1296 and EN 1297, reaction to fire to EN 13501-1 and external fire performance to EN 13501-5 with EN 1187, along with dimensions and mass. What it does not do is grade the product or classify it as SBS or APP. Two sheets can both conform and be very different, so asking for a membrane "to EN 13707" specifies a framework rather than a performance level. Write the required declared values into the specification.
Which ASTM standards cover SBS and APP membranes?
Five product specifications, divided by modifier and by reinforcement. For SBS: ASTM D6164 for polyester reinforcements, D6163 for glass fibre reinforcements and D6162 for a combination of polyester and glass fibre. For APP: ASTM D6222 for polyester reinforcements and D6223 for the polyester and glass fibre combination. All five call up ASTM D5147 as the test method standard, which covers sampling and the determination of thickness, mass, peak load, ultimate elongation, tear strength, low-temperature flexibility, dimensional stability, compound stability and granule embedment. D5147 sets no acceptance limits itself; those are in the five product specifications, expressed by type and grade. Read the limits from the current edition of the relevant specification.
Does this site supply finished waterproofing membranes?
No. This site supplies bitumen, not membranes. We do not manufacture or sell membrane rolls, torches, cold adhesives, primers or granules. What we supply is the material membranes are made from and laid in: oxidised bitumen in the blown grades used in membrane manufacture and as hot mopping asphalt, polymer modified bitumen, and penetration-grade bitumen as a base for modified compounding. If you are buying finished rolls, buy them from a membrane manufacturer against a Declaration of Performance or an ASTM-conforming technical data sheet for the specific product. If you are making membranes, or specifying the mopping asphalt for a hot-applied system, that is the part of the chain we are in.
Buying the bitumen behind the membrane?
Send the grade you need — an oxidised designation such as 85/25 or 115/15, an ASTM D312 type for mopping asphalt, a penetration grade as a compounding base, or a polymer modified binder — together with quantity, packing, destination port and Incoterm, and any national standard the material has to satisfy. Middle East supply is quoted against the specification you send, with a Certificate of Analysis for the batch. We supply the bitumen; the finished membrane rolls come from a membrane manufacturer.