..

offer

by Mark S. Graham

uring the past decade, theuse of polymer-modifiedbitumen membrane roofsystems has grown substan-

tially. According to NRCA's 1996 An-nual Market Survey, use of such roofsystems is 18.1 percent of the totalroofing market (calculated on adollar volume basis) in the UnitedStates.

Roofing professionals and build-ing owners have a large number ofpolymer-modified bitumen mem-brane products from which tochoose. According to NRCA's 1997Commercial Low-Siope Roofing MaterialsGuide, there are 359 different modi-fied bitumen sheet membrane prod-ucts available on the market from 36

different manufacturers. Of theseproducts, 95 are identified as APP-modified bitumen sheets, and 258are SBS-modified. Six products areidentified as "other" modified bitu-men sheets.

The materials guide also identifies932 different roof system specifica-tions that use modified bitumensheet membrane products.

This article will briefly explain thehistory of polymer-modified bitu-mens, discuss a number of impor-tant considerations to evaluate whencomparing these products andexplain the status of material stan-dard development for polymer-modified bitumen sheet roofingproducts.

HistoryPolymer-modified bitumen roofingtechnology, as it is known today, wasdeveloped in Europe in the 1960s.Products first were introduced intothe market predominantly in Italyand Belgium.

The first recorded use of polymer-modified bitumen sheet membraneproducts in the United States was in1975. Early product introductionsoften were categorized as single-plymembrane roof systems. This waspartly due to the single-layer appli-cation method often used at thattime-a polymer-modified bitumenmembrane sheet was applied directlyto a substrate without a base sheet ormembrane base plies.

Also, because the product was in-troduced at nearly the same time asconventional single-ply membranes,polymer-modified bitumen mem-branes and single-ply membranesoften were classified together, largelybecause they were viewed as differentfrom built-up membrane systems. Infact, the first edition of The NRCARoofing and Waterproofing Manual(1981) categorized polymer-modified bitumen roof systems andmost single-ply membrane roof sys-tems as synthetic or special mem-brane systems.

As the use of these products be-came more widely accepted in theU.S. market in the early to mid-1980s,

24 Professional Roofing August 1997

,

membrane sheet with increased punc-ture resistance and some elongationcapabilities. Membrane products witha combination (or com~te) offiberglass and polyester reinforce-ments attempt to capitalize on theatttibutes of both reinforcements.

Also, the specific type of polyesterreinforcement can have an impacton the membrane sheet's physical

polymer-modified bitumen productswere differentiated from single-plymembranes. Also, the need to apply apolymer-modified bimmen mem-brane to a base sheet or base mem-brane plies was recognized. At thispoint, the product began to be con-sidered its own membrane type. Thesecond edition of The NRCA Roofingand Waterproofing Manual (1985) list-ed it in a polymer-modified bimmenroofing category, separate fromsingle-ply membranes.

During the late 19805 and early1990s, the use of polymer-modifiedbitumen membrane roof systemshad grown significantly. By this time,polymer-modified bitUmen mem-brane products were used in tworoof system configurations: aspolymer-modified bitUmen mem-brane roof systems and topmost lay-ers in multiple-ply built-up mem-brane roof systems, also known ~hybrid roof systems. (For more infor-mation about hybrid roof systems,roofing professionals should refer to"The hybrid system is created bymerging roof system featUres," Octo-ber 1995 issue, page 20.)

Product differencesWith the large number of polymer-modified bitumen sheet products onthe market, it is important to realizethere are significant product differ-ences to consider. Following is a listof some factors that should be con-sidered when evaluating polymer-modified bitumen membrane sheet

products:1. Bitumen modifier. Polymer-

modified bitumen membrane sheetsare different from most other mem-brane types because the waterproof-ing bitumen in the membrane sheetis chemical1y altered. The specifictype of polymer modifier employedalso can be used to differentiate be--tween polymer-modified bitumenmembrane products themselves.

One of two polymer modifiers,APP or SBS, is used in a vast majorityof the polymer-modified bitumenproducts currently on the markeLThe most noticeable differencebetween polymer modifiers is the

manner in which the membranesheets are applied. APP-modifiedbitumen sheets typically are torch-applied. and SBS-modified sheetsgenerally are mopped in place. Bothtypes also can be adhered with acold-applied adhesive.

However, the most significant dif-ference between polymer modifiersrelates to the materials' chemistryand its resultant effect on the prod-uct. APP-polymer modification cre-ates bitumen molecules that are en-capsulated with the polymer modifi-er. This gives the resultant mem-brane plasticized properties and rais.-es its softening-point temperature.Conversely. SBS-polymer modifica-tion creates molecular bond., be-tween bitumen molecules. This givesthe resultant membrane rubberized

properties.For these reasons, the physical

properties of APP- and SBS-J>olymer-modified bitumen sheets will varysignificantly-this is intentional andinherent in the different polymermodifiers. Therefore, direct com-parisons between APP- and SBS-polymer-modified bitumen productsare not practical.

2. Bitumen. Asphalt is the onlyroofing bitumen used in compoundpolymer-modified bitumen sheetproducts. However, in the mid-l990s,one manufacturer did produce acoal tar-based polymer-modifiedproduct. Because of the inherent dif-ferences between asphalt and coaltar bitumen chemistry, direct com-parison between products based ondifferent bitumens is not practical.

3. Reinfon:ement rype. Most polymer-modified bitumen sheets contain re-inforcement of some form of fiber-glass or polyester fabric or a combi-nation of both fiberglass and poly-ester. Because different types of rein-forcement give membrane sheetsdifferent physical properties, carefulconsideration of the reinforcementtype is necessary when comparingproducts.

Fiberglass reinforcements gener-ally provide a membrane sheet withhigh tensile strength. Polyester re-inforcements typically provide a

August 1997 PtrJfasional Roofing 25

properties. For example, a wovenpolyester reinforcement likely willprovide better tensile strength thana nonwoven one. However, wovenpolyester usually will allow less elon-gation capacity than nonwoven. Forthis reason, it is difficult to directlycompare membrane sheets that usedifferent reinforcements.

4. Reinforcement weight. Manypolymer-modified bitumen sheetsuse similar, if. not identical, rein-forcement types. However, some

about the middle of the membranesheet thickness. However, in someproducts, the reinforcement is posi-tioned toward the membrane sheet'stop surface. Reinforcement place-ment impacts the membrane sheet'shandling and installation and mayaffect the material's physical proper-ties and performance.

6. Surfacing. Polymer-modified bi-tumen products are available eitherunsurfaced or with a variety ofdifferent factory-applied surfacings.

sheets employ lighter or heavier rein.forcements; this is particularly thecase with polyester reinforcements.Because reinforcement weight andits configuration play importantroles in the physical properties ofpolymer-modified bitumen sheets,products with different weight rein-forcements should not be consid-ered similar.

5. Reinforcement placement. In mostpolymer-modified bitumen sheets,the reinforcement is positioned in

Dealing with polymer-modified bitumen roofsystem warrantiesby Stephen M. Phillips

Warranties offered by polymer-modified bitumen manUfac-turef$ are similar to thOSe applicable to built-up roof (BUR)systems. Indeed, several manufacturers of both mOdifiedbitumen and BUR materials use the same warrantydocu-ments for bOthprriducts. JUst as BUR manufacturers offer20-year warranti~for certain four-ply specifications, 20-year warranties (With no monetary limitations) are offeredby several modified bitumen manufacturers.

Similar to other roof membrane warranties, modified bitu-men warranties can be divided into two broad cat~ories:warranties covering bOth materials and worf<manshipand those covering onfythemodified bitumenmatelial.For a fee, most manUfaCturers offer warranties that covetthe worf<manship of the contraCtor who installed the~ifi~ bitumen membrane, provided the contractorIS approved by the manUfacturer and follows itss~ifications.

Asw~halmostall r~f membrane warrant.ies, .most modi-fied bitumen warranties cover leaks only (I.e.. If a leak's~use is covered by the warranty, the manUfacturer will payiortherepairs). As long as the roof system is watertight, themanUfacturer is not required to take any action.

Warranties covering materials and workmanship are avail-abfe at no charge orat.feesup to $20 per square (1 squareequals 9.3 m2), depending on the manufacturer and lengthof warranty. Most material-only modified bitumen war-ranties cover manufacturing defects and are available atno cost, though a few manufacturers charge.

the ..length of coverage format?rials and workmanship.ranges from fIVe to 25 years, with 15- and 20-year war-ran~esbeingt~emostcommon. The ..length <:>f.cov~gey~nes,dependlngonthe manufacturer ,spec~~modifi~bitumen product and the roof s~temcompo~itlon. Modl-fi~bitumen sheets commonly are i~orporated into roofassemblies that include under1ying BURie/ts.Thenumber

of plies frequently will determine the length of warrantycoverage available.

Careful attention should be given to asphalt selection andapplication, as well as whether the roof system's bitumencom~nent isinqluded in the warranty coverage. If themodified b!tumen warranty truly is a system warranty, bitu-men. used to adhere an SSS-modified bitumen sheet..should be included in the coverage. Many modified bitu-men warranties exclude coverage for products not soldby 100 manufacturer. If a contractor does not purchaseasphalt through the modified bitumen manufacturer, therelikely wi..llbe no warranty coverage if a roof problem oc-curs due 10 some incompatibility betWeen the asphaltand modified bitumen sheet or an alleged defICiency inthe aspf'!alt.

Even though the modified bitumen manUfacturer may notbe the ~phalt manufacturer, purchasing asphalt throughthe modified bitumen manufacturer will provide more ex-tensivewarrantycoverage. If a contractor doas not pur-chase asPhalt from the modified bitumen manufacturer,he should obtain written confirmation from ~th the asphaltand modified bitumen manufacturers that their productsare compatible and ~ssess the neces~propGrties 10pGrlormiogether satisfactorily.A roof s~tempurchaser should make a similar decisionregar:ding roof..insulation. If the insulation ..is purchased1hrough a modified bitumen sheet manufacturer.. there maybe warranty coverage. Some manufacturers provide war-rantycoveragefor ~ific insulation products. If there iscov~rag,e ~orin~ulatio~, a manufacturermaywarrantth~tth$ Insulation WIll provide at least 80 pertent of the designthermal resistance in addition to the "watertight" membranecQverage.Unlike shinglewarranti~, those for modified bitumen gen-erallyarenot prorated (I.e., the extent of the manufacturersliabjl'tvdoesnQt decrease by acertaJn percentage eachyear).. HQwever,a few are prorated-sQ the monetarylimIt Qf.themanufacturer's liabil'tvis reduced as each year~.If a bu!ldin9 owner contemp.lates selling a buJlding within10 years of roof system installation, warranty transferabilitymay be an imPQrtant factor. If there is no provision in thewarranty!egarding transferability or assignability, then the

26 ProfessWnal Roofing August 1997

may affect the membrane sheetproduct's physical properties. For ex-ample, a metal foil surfacing likelywill enhance the membrane's tensilestrength and its resistance to chemi-cal exposure.

For these reasons, surfacing typeshould be considered carefully whencomparing polymer-modified bitu-men membrane products.

7. Other consideratWns. A number ofother important factors, including thesource and quality of raw materials,

Factory-applied surfacings includemineral and ceramic granules, min-eral chips and metal foils. Membranesurfacings also can be field-appliedas additional components of the roofmembrane system.

Because the top surface of anSBS-polymer-modified bitumen roofsystem must protect the membranefrom ultraviolet degradation, manySBS-polymer-modified bitumens con-tain factory-applied surfacings. Insome instances, surfacing material

bitumen and polymer blending. aswell as manufacturing tolerances andquality control. can influence the performance of polymer-modified bitu-men sheet products. Unfortunately.most roofing professionals and. insome cases. manufacturen, do nothave the capability or equipment toevaluate these facton direcdy.

As a result, roofing professionalsoften need to rely on the limited ap-plicable material standards and anyphysical property data available

manufacturer's liability varies and can become a criticalfactor if a serious roof system problem arlS8$. The mone-tary scope of modified bitumen warranties ranges from thecost of the modified bitumen product to no limitation O.e.,a so-called "nO-doilar-limit" warranty). Some modified bItu-men warranties are limited to the product's original cost orstipulated-per-square dollar amount.

Before deciding on a particular modified bitumen roof as-sembly and warranty. a specifier should obtain clarifICationfrom the manufacturer when the phrase "original cost of theproduct" is used In a warranty: Does it mean the manufac-turer's liability is limited to the modified rnernbrane sheetmaterial's cost,or does "product- refer to the overall modi-fied bitumen roof assembly, which would include labor andmaterials? Arefttedy limited to the sheet goods' costs onlywould cover a fraction of the expense incurred to removeand replace a nonperformfng modified bitumen roofassembly.

ConclusionA decision regarding what type of roof system to installshould be based on a roof system's properties and its suit-ability for a partiGUlar application rather than a warranty. A.well-performing roof system makes warranty coverage Ies$,significant; conversely, an extensive, long-tenT1 warranty .provided by a manufacturer who is in bankruptcy or nolonger in busineSS Is of no value.

Nevertheless, before making a roofing decision, a manufac-turer's warranty should be considered and evaluated. Simi-lar to all legal documents, a modified bitumen warrantyshould be read and understOod in its entirety as part of1heinitial system sPecification and selection process. Althoughall manufacturers' warranties generally provide for repairto leaks caused by either materials and workmanship ormaterials only, there are significant differences regardingsuch items as monetary limitations, cost to obtain the war-ranty, exclusions from coverage, wind coverage and trans-ferabi.lity. General~, manufacturers will offer a longer war-rantyfor modified bitumen roof systems Inco~ratlng moreplies or more durable (and expensive) modified bitumenproducts.

-. - ~ ~

Stephen M. Philupsisa ~ with the law ~H".a~Phillih~ &hemm&Sau.man Atlan'" Ga, aM~lJ$r' , ..., . " "counsel to NRG'1.

warranty, like other legal documents, can be transferred orassigned to a subsequent owner.

However, some modified bitumen warranties specificallystate they are nontransferable-meaning only the originalowner would be entitled to warranty coverage. Other war-ranties contain specific transferability provisions, generallyrequiring payment of a transfer fee, a roof inspection andcompletion of any manufacturer-directed roofing work atthe owner's expense pl1or to the warranty's transfer.

Obtaining a warranty can, in certain circumstances, havethe effect of limiting a building owner's remedies. Althougha warranty commonly is viewed as a means of obtainingprotection in the event of a problem and generally servesthis purpose, modified bitumen warranties, like other war-ranties, frequently contain provisions seeking to make thewarranty an owner's sole and exclusive remedy.

For example, if there Is a problem during the first few yearsafter roof system installation, an owner might have greaterrecourse without a specifIC warranty-which actually mayrestrict him, depending on the problem's cause and applic-able state law. However, if an owner does not purchase $materials and workmanship warranty, a manufacturer typi-cally would not be liable for any deficiency in the modifiedbitumen membrane application and the length of the manu-facturer's liability would be governed by the state statute oflimitations.

In most states, the statute of limitations for warrantiesunder the Unifonn Commercial Code is four years. In somestates (e.g., Florida, New York), an owner cannot make aclaim for roof system repair or replacement directly againsta manufacturer in the absence of a warranty. The warrantyhas the effect of establishing privity of contract betweenthe owner and manufacturer.

Although the cost to obtain a materials and workmanshipwarranty generally will increase as the length of coverageincreases, the cost to obtain a warranty for a given periodvaries considerably among manufacturers. For example, a15-year materials and workmanship modified bitumen war-ranty can cost from $5 to $15 per square, and the cost ofa 2O-year materials and workmanship warranty varies from$7.50 to $20 per square.

Just as the cost will vary, the monetary scope of the

27August 1997 p, !Ssiooal Roofi~

when comparing polymer-modifiedbitumen sheet membrane products.

minimum properties and provide abaseline for evaluating these prod-ucts has been slow.

Up to this point. Canadian Gener-al Standards Board (CGSB) Standard37-GP-56M, "Standard for Mem-brane, Modified, Bituminous, Prefab-ricated, and Reinforced for Roofing"has been the only material standard

Material standardsEven though polymer-modified bitu-men membrane products have beenused in the United States for morethan 20 years, the development ofmaterial standards to establish

applicable to poiymer-modified bitu-men sheet products in North America.This standard includes requirementsfor product strength. water resistance.flexibility and divisibility. It aOO sepa-rates products into two grades (stan-dard and heavy-duty); three classes(Qass A-granule surfaced. Qass B-melallic surfaced and Qass c-plain surfaced); and two types (1}"J>eI-exposed applications and Type 2-covered roofing applications).

CGSB 37-GP-56M is referencedin The BOCA National Building Codeas a minimum material requirementof polymer-modified bitumen roofcoverings.

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Physical property dataBecause of the many differences inproducts, reviewing published physi-cal property data is one practicalmethod of evaluating and compar-ing polymer-modified bitumen sheetproducts.

American Society for Testing andMaterials (AsrM) Standard D 5147,"Standard Test Methods for Sam-pling and Testing Modified Bitumi-nous Sheet Material," was developedto provide a standardized methodfor testing and reporting physicalproperty data for polymer-modifiedbitumen sheets. It includes testmethods for thickness, load strainproperties, tear strength, moisturecontent, water absorption, dimen-sional stability, low-temperature flexi-bility, heat conditioning, acceleratedweathering, granule embedment,compound stability and compoundthickness.

Although most manufacturers reg-ularly test their products accordingto this method, few publish their testdata and make it available to roofingprofessionals and building ownersfor product comparison. Accordingto NRCA's materials guide, only 19of the 36 manufacturers listed pro-vide any physical property data.

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During the June ASTM D-8 commit-tee meeting in St. Louis, Mo., threenew material standards applicable toSBS-polymer-modified bitumen sheetCheck "0", ~ s.wa c.fJ

28 Professional Roofmg August 1997

~

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manufacturers are encouraged tomake additional technical and ph}!Si-cal property data available in theirproduct literature and NRCA's mate-rials guide. This would help roofingprofessionals and building owners

make infonned decisions when com-paring and purchasing manufactur-ers' products. ~

products were given final approvcIJ:"Standard Specification for StyreneButadiene Styrene (SBS) ModifiedBituminous Sheet Materials UsingGlass Fiber Reinforcements," "Stan-dard Specification for Styrene Buta-diene Styrene (SBS) Modified Bitu-minous Sheet Materials Using Poly-ester Reinforcements" and "StandardSpecification for Styrene ButadieneStyrene (SBS) Modified BituminousSheet Materials Using a Combina-tion of Polyester and Glass FiberReinforcements. "

Mam S. Graham is NRCA's associatee%«u.tive di1?dor of technical senIiCG.

Manufacturers have givenlittle quantitative information

to compare polymer-modified

bitumen sheet products.

ASTM will publish these threematerial standards later this year-they will provide minimum require-ments for SBS-polymer-modified bi-tumen sheet products that roofingprofessionals can use to evaluate SBSproducts. When the standards arepublished, SBS-polymer-modified bi-tumen sheet products' manufactur-ers are encouraged to clearly repre-sent and label their products in ac-cordance with the standard.

New material standards applicableto APP-polymer-modified bitumensheet products are in the final stagesof development at ASfM. It is hopedthese standards will be finalized andpublished within the next few years.

Closing thoughtsDuring the past decade, use ofpolymeI'-modified bitumen sheetproducts has grown tremendously.This has established polymer-modified bitumen roof systems as vi-able and sometimes preferred choic-es in many situations. However, up tothis point. manufacturers have givenroofing professionals and buildingowners lime quantitative inforDla-lion to compare polymer-modifiedbitumen sheet products.

Polymer-modified bitumen sheet Check 162 «I ,...,. Swwke c.d

August 1997 Professional Roofing 29