protected membrane roof first to last - suppliers -...

Protected Membrane Roof

First to Last

C O M M E R C I A LUnited States/Canada

PMR Brochure 1/22/07 10:50 AM Page 2

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow

Nearly 40 years ago, someroofing experts from The DowChemical Company took acompletely new look at theways roofs are designed. Quiteliterally, they turned theindustry upside down.

The protected membraneroof (PMR) has represented thebest in flat roof technologysince it was developed in1970. The PMR concept wassimple yet radical. A PMRincorporates an “upsidedown” approach to insulatingthe roof: placing the insulationon top of the waterproofmembrane. While expertsbelieved this design wouldimprove the membrane’seffectiveness and the insula-tion’s efficiency, few could

How a BreakthroughIdea Revolutionizedthe Roofing Industry

have foreseen the dramaticresults that PMR assemblieshave delivered to buildingowners: Some of these originalroof membranes remain inexceptional condition, nearly40 years after installation.

Why did this breakthroughtake so long to happen? Easy:because no insulation hadever proven durable enoughto withstand exposure to theenvironment like STYROFOAM™

extruded polystyrene insula-tion. Once it began to be usedas a roof insulation, roofingexperts saw the possibility fora new, effective technology.

And the protected membraneroof was born.

In a protected membrane roof

assembly, the insulation is placed

on top of the membrane, improvingthe performance andlongevity of the roof

system.

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Taking “Cost-Effective”to a New Level

A protected membrane roofis cost-effective. It is an assemblythat performs year after year –and the longer a roof can be keptin use, the more it contributesto the overall sustainability ofthe building by delaying theimpact of eventual tear-off.

Building owners must considerthe time value of money overthe life of the building – notjust the up-front constructioncosts. Using a PMR can reduceannual maintenance costs andincrease the life of the roof.For example, deferring a roofreplacement by 10 years –which is often the incrementaldifference between the life spansof PMR and conventionalroofs – can save hundreds ofthousands of dollars.

In commercial roofing,maintenance costs can be significant if patching, cleaningor rejuvenating is required.When PMR assemblies areinstalled, the membrane isusually not visible, and is notsubject to any of the primeforces of deterioration. Inindependent studies, PMR systems have been shown tohave significantly lower maintenance costs than conventional low slope roofs.For a 50,000 ft2 (4,645 m2)roof, reducing the maintenancecosts from 3 percent of initialroof cost to 1 percent of initial

roof cost provides a significantcost savings that can be investedin the lower-maintenance roof.The investment is paid back inless than seven years, after whichthe savings in maintenancecosts continue to help theoperations budget.

Long-TermPerformance?Try 30 years (or more)

Consider the conventionalroof, which may last 15 years.At the end of its useful life, itwill be disposed in a landfill.This process is costly for thebuilding owner, who pays forthe tear-off of the old roof andthe installation of a new system,and also costly for society, whereconcern over the environmentalcosts of the constructionindustry is growing. A truelife-cycle cost decision willinclude all of these factors inits final analysis.

By contrast, a PMR assemblythat lasts 25 to 30 years (orlonger) helps to alleviate manyof those costs. Or, at the veryleast, greatly reduces the fre-quency of tear-offs – a benefitto the building owner as wellas to the environment.

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By any standard, Michigan State University in EastLansing, Mich., is a massive place. In terms of thesheer number of students and the size of thecampus, MSU is one of the nation’s largest universities.

Established in 1855, Michigan State is, obviously,here to stay. That’s why MSU places long-termperformance and durability as a top priority for its many buildings.

Some of the earliest protected membrane roofswere installed on MSU buildings in the late 1960s,and many more have followed in the past 40 years– a total of 161 buildings on campus.

“We are very happy with the inverted (PMR)roof,” says Budd Pulver, Michigan StateUniversity’s roofing supervisor. For Pulver and therest of the staff who maintain MSU’s extensiveinfrastructure, PMR provides a number of benefits:

DURABILITY: Some roof decks are used as plazas,which means the roof must support foot traffic.

STRENGTH: Construction projects are constantlycarried out on campus. This means equipmentand building materials are often placed on topof PMR assemblies during the constructionphase. “Protected membrane roofs provideprotection during construction of new additions,”Pulver says.

LONGEVITY: “Some of the PMR assemblies willprobably last 50 years,” says Pulver without hesitation.

WIND RESISTANCE: “When a roof deck is 100 feetoff the ground, a 20 mph wind can feel morelike 80 mph,” says Pulver. With a conventionalroof, the wind sweeps across the unprotectedmembrane. But with a PMR, the wind simplysweeps across the stone, and the membranestays protected.

MEMBRANE PROTECTION: Given Michigan’s climate, temperatures vary widely throughoutthe year. This up-and-down variation candegrade an exposed membrane that enduresrain and sunlight, frigid cold and blistering heat;but thanks to the inverted structure of PMR, themembrane is kept away from the damagingeffect of weather. The benefit for MSU is adecrease in maintenance and repair costs onmany of its roofs.

W H Y P M R I S P E R F E C T F O R M S U

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Photo courtesy of University Relations, Michigan State University


PMR systems require a minimum ballast of 10 lb/ft2 (50 kg/m2)when used with a Fabrene* scrim sheet. Additional ballast

is required at perimeter areas, curbs, pony walls, etc. For alighter-weight PMR, consider using a T. Clear system withLightguard** in the U.S.

Questions About PMR?DOW HAS THE ANSWERS

Building decisions are not made lightly. And although youmay agree that a PMR assembly is a great choice, you likely have additional questions. Let’s address some of the commonquestions that are asked about PMR.

Is a PMR too heavy for my building?Q:

A:

No, because pressure equalization offsets the effect of wind uplift. In a lightweight PMR – with insulation loose-

applied on the membrane and covered with 10 lb/ft2 (50 kg/m2)of ballast – external pressures due to wind are mostly applied to the membrane.

The membrane will withstand the National Building Code calculated pressure if it is properly attached to the deck. In thecase of a loose-applied membrane, it is important to prevent any air infiltration underneath the membrane. When air infiltration is restricted, any movement of the membrane willcreate a vacuum that will neutralize the uplift forces and keepthe membrane on the deck.

Will my PMR roof blow off?Q:

A:

Actually, a PMR will save money in the long run. Considerthese advantages of a PMR, which directly impact your

bottom line:• The building can be weatherproofed faster, allowing interior

trades to start work quicker. This gives greater flexibility in theconstruction timetable.

• The insulation is laid after the membrane – and can be laid inany weather.

• Greater quality control is possible, as the membrane can beinspected or flood-tested before insulating and ballasting.

• Because the PMR system uses fewer components than manyconventional roof systems, the overall labor costs and materialcosts may be reduced.

• Life-cycle cost analyses show a higher initial capital cost for aPMR, but lower maintenance and longer roof life span offsetthese initial costs.

Is a PMR too expensive?Q:

A:

*Fabrene is a registered trademark of Fabrene, Inc., a wholly owned subsidiary of Polymer Group, Inc.**Lightguard is a registered trademark of T. Clear Corp.

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In loose-laid membrane systems, it is true that water canenter the building far from the actual location of the leak.

However, if the membrane is fully bonded to the deck, thiswater remains at the location of the leak. And in the case of aleak, the PMR is far easier to repair, because all of the originalmaterials can be reused – an environmentally friendly featurethat will save you thousands of dollars.

Is it difficult to find a leak in a PMR system?Q:

A:

The insulation, ballast and approved scrim sheet are intendedto float temporarily after periods of heavy rain, or if control

flow drains are required in your area. The Cold Regions Researchand Engineering Laboratory (CRREL) of the U.S. Army Corps ofEngineers studied the reduction of R-value due to ponding on aPMR. Their report found an R-value or RSI reduction duringperiods of cold rain, but the report went on to point out thatthe same effect reduces heat gain during air conditioning periods.

Will my insulation float (and reduce my R-value† or RSI)?Q:

A:

Remember: STYROFOAM™ extruded polystyrene insulationhas the lowest moisture absorption of any insulation in

the marketplace today. If any insulation can handle moisture,it’s STYROFOAM.

It is also true that all insulation, including Dow products, canbecome saturated if a “diffusion closed” situation occurs. Thishappens when the insulation is sandwiched between the vaporbarrier and the roof deck (such as when pavers are placed directlyon the foam, preventing vapor from escaping so it is drivenback into the foam). Constant ponding can also lead to thiscondition. To avoid diffusion closed situations, provide for agood slope to drain in your roof design (a minimum of 1/4"slope per foot) and ensure impermeable roof coverings, such aspavers, are installed on pedestals so that vapor can escape.

Will my insulation get wet?Q:

A:

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow†R means resistance to heat flow. The higher the R-value or RSI, the greater the insulating power.

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Sustainability in the Roofing IndustryWHY PMR IS THE ANSWER

In the 21st century, sustainable building practices are moreimportant than ever. And many North American cities are making sustainability a requirement, rather than an option. In a number of ways, the PMR assembly helps building ownersmeet the goal of sustainable construction – including contributingto the achievement of LEED†† points.

SUSTAINABILITYOBJECTIVE

Reduce the total energyconsumption of the building (life-cycle costing)

Reduce global warmingimpact from excessivelyusing energy sources(reduce)

Reduce the downstreamwaste during construc-tion, maintenance anddemolition phases(reuse, recycle)

Offer recycled contentand/or environmentallyfriendly reusable prod-ucts (recycle)

PMR BENEFIT

PMR performs year after year – and the more a roof can be kept in use, the more it contributes tothe overall sustainability of thebuilding by delaying the impact of eventual tear-off.

A PMR using a rigid, extruded polystyrene insulation, with one ofthe highest R-values per inch, willrealize reductions in utility bills,year after year. By reducing HVACloads, this will lower pollutionemissions from burning fossil fuels.

Because the insulation, fabric and ballast are loose-laid in a PMR,many times these components canbe reused after maintenance ormajor construction.

Dow incorporates recycled materials into its finished goods.For example, Dow has been internally recycling trimmings fromthe production of STYROFOAM™

extruded polystyrene for more thanfour decades. Scrap, such as cuttingsfrom board edge treatments, isrecycled back into finished products,reducing waste and storage andlandfill costs.

††The U.S. Green Building Council, a nonprofitcoalition promoting high-performance greenbuilding design, has developed Leadership inEnergy and Environment Design (LEED), a volun-tary, consensus-based standard. The LEED ratingrecognizes the life-cycle costing of construction.

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From GreenBuildings to Green RoofsPMR is the perfectpartner

The protected membrane roofprovides the ideal foundationfor a sustainable building solu-tion. Whether you are seekingto obtain LEED points, or areplanning an earth-friendlygreen roof, a roof that leavesthe membrane protected is anessential component.

Situated on 10 acres indowntown Salt Lake City, The Conference Center is an imposing presence.Completed in 2000, the Centerseats more than 21,000 peopleand is the world’s largest religious auditorium.

One of its most strikingfeatures is its 70,000 ft2

(6,500 m2) rooftop meadow– a massive re-creation of thewild landscape of Utahmountains featuring 21 typesof Utah grasses and 300 vari-eties of native wild flowers.

The rooftop meadow helpsSalt Lake City battle the“urban heat island” effectthat is common to largecities. One remedy is to addvegetation to downtownareas; “urban forests” likegreen roofs keep cities coolbecause a large portion ofsolar energy is required toevaporate water from vegetation and soil. As aresult, asphalt absorbs lessenergy and increases in temperature are smaller.

The foundation for TheConference Center’s remarkableurban garden is a protectedmembrane roof, featuringSTYROFOAM™ extruded polystyrene insulation fromDow. STYROFOAM extrudedpolystyrene is an ideal com-ponent of any green roofproject, providing the waterresistance and compressivestrength necessary to supportthe heavy soil loads of thisenvironmentally friendlyassembly.

G R E E N R O O F B E G I N S W I T H P M R

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Photos courtesy of American Hydrotech, Inc.



To understand why PMRrepresents such an importantstep forward, it helps to lookat how it differs from a conventional roof.

Conventional roofs havealways been constructed thesame way: with the membraneplaced on top of the insulation.With the conventionalarrangement of roofing materials – roof deck, vaporretarder, insulation, waterproofmembrane – the insulation isprotected from the exteriorenvironment; however, in thisarrangement the membrane isseparated from the roof deck.Because it is no longer keptwithin a moderate temperaturerange that is near the building’stemperature, the membrane is subject to a new set of conditions and stresses.

A conventional roofingarrangement can leave thesensitive membrane vulnerableto extreme and often suddentemperature changes, high

summer roof temperatures,lower winter temperatures,freezing puddles, ultravioletrays, interior moisture thatcould penetrate the insulation,and physical abuse fromheavy foot traffic and routinemaintenance. Exposure to allof these elements weakens theintegrity of the membrane. Oncethe membrane is compromised,moisture will eventually enterthe insulation and cause a lossin its thermal efficiency.

TemperatureVariation on aConventional Roofis Extreme – and ExtremelyDamaging

On a sunny winter day, thetemperature of a roofingmembrane can experience aone-day change of 100°F (55°C).Here’s how: In cold areas ofNorth America, the temperatureof a roof will mirror the airtemperature in the pre-dawnhours. But during the courseof a clear, cloudless winterday, sunlight can drive themembrane’s temperature up –much warmer than the airtemperature. This extremefreeze-thaw cycling – whichrepeats many times in a typicalyear – can take a heavy toll onthe roofing membrane in aconventional roof. The resultis a series of cracks, blistersand an “alligatoring” patternof damage on the membrane.

Figure 1: Conventional Roof

The Need for a Better Roofing SystemPMR VS. CONVENTIONAL ROOFS

Membrane

WeatheredMembrane

Insulation

Deck

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PMR 101: How theElements of PMRWork Together

All conventional flat roofassemblies consist of the samebasic elements, which areassembled in a seemingly logical order: a deck (composedof wood, metal or concrete)covered with insulation andtopped with a waterproofingmembrane (see Figure 1).

While protected membraneroof assemblies often employthe same elements, the order ischanged. The membrane ispositioned UNDER the insula-tion, which protects the membrane and thus providessuperior long-term performanceand durability (Figure 2).

With a PMR assembly:• The membrane is main-

tained at a nearly constanttemperature – close to thetemperature of the building’sinterior. This reduces theharmful effects of freeze-thawcycling and excessive heat.

• The membrane is protectedfrom weathering, foot trafficand other physical abuse,during and after construction.

• The roof is waterproofedfirst and insulated second –which allows for year-roundconstruction.

• Removal and re-installationof the ballast (for repairs or toconstruct additional stories)and insulation is easy. Andinsulation can be reused.

• Many ballast options – suchas stone, precast paving slabs,green roof, interlockingstone or concrete – can beused in conjunction with aPMR. And PMR assembliesare compatible with a rangeof membrane types as well.

Figure 2: PMR Roof Assemblies

Concrete Ballast

Plaza Deck

Green Roof

Membrane

Stone

Fabric

Deck

STYROFOAM™Extruded PolystyreneInsulation

Stone Ballast

Membrane

Concrete

Deck

STYROFOAM™ Extruded Polystyrene Insulation

Filter Fabric

Membrane

Pedestals

Deck


Membrane

Vegetation

Deck


System Filters

Soil

Filter Fabric

Drainage Layer

Pavers



Dow Products are Keyto PMR Performance

With the membrane posi-tioned under the insulation,the choice of insulationbecomes a key consideration.The insulation in a PMRassembly must be able towithstand wet environments(without sacrificing insulationperformance) and foot traffic.

That’s why durable, moisture-resistant STYROFOAM™ extrudedpolystyrene insulation is theideal choice for PMR.

STYROFOAM extruded polystyrene insulation has aclosed-cell structure, whichmeans water is inhibited frompenetrating the insulation andreducing its thermal efficiency.The impressive physical properties of STYROFOAMextruded polystyrene insulationproducts (see Tables 1 and 2)help to ensure the long-termreliability of a PMR.

Physical Properties of STYROFOAM™ Extruded Polystyrene Insulation, U.S.

TA B L E 1

Property and Test Method Value

Thermal Resistance, typical 5-year aged R-value, ASTM C518, ft2•h•°F/Btu 5.0 Coefficient of Linear Thermal Expansion, ASTM D696, in/in•°F 3.5 x 10-5

Compressive Strength, ASTM D1621, psi, min.STYROFOAM™ ROOFMATE™ 40STYROFOAM™ Ribbed ROOFMATE™ 40STYROFOAM™ PLAZAMATE™ 60STYROFOAM™ Highload 40 40STYROFOAM™ Highload 60 60STYROFOAM™ Highload 100 100

Water Vapor Permeance, ASTM E96, perm, max. 0.8Water Absorption, ASTM C272, % by volume, max. 0.1Maximum Operating Temperature, °F 165

Physical Properties of STYROFOAM™ Extruded Polystyrene Insulation, Canada

TA B L E 2

Property and Test Method Value

Thermal Resistance, typical 5-year aged R-value (RSI), ASTM C518, C177ft2•h•°F/Btu (m2•°C/W) 5.0 (.88)Coefficient of Linear Thermal Expansion, ASTM D696, in/in•°F (mm/m•°C) 3.5 x 10-5

(6.3 x 10-2)Compressive Strength, ASTM D1621, psi (kPa), min.

STYROFOAM™ ROOFMATE™ 35 (240)STYROFOAM™ ROOFMATE™ DC 35 (240)STYROFOAM™ Highload 40 40 (275)STYROFOAM™ Highload 60 60 (415)STYROFOAM™ Highload 100 100 (690)

Water Vapour Permeance, ASTM E96, perm (ng/Pa•s•m2), max. 0.8 (46)Water Absorption, ASTM D2842, % by volume, max. <0.7Maximum Operating Temperature, °F (°C) 165 (74)

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I N S I D E I N S U L A T I O NTo insulate is to prevent the transfer of

heat. Insulation is formed by trappingair in a material. But not all insulatingmaterials are created equal. The morecompartments of air across a given spanof material, the greater the thermalresistance (R-value or RSI).

Insulating sheathing from Dow contains thousands of tiny pockets oftrapped air in every square inch ofmaterial. Proprietary formulations andmanufacturing processes ensure thatthese closed cells are consistent in size.

An insulation’s performance is greatlyreduced when the trapped air is able tocirculate or move freely. This happensprimarily through air infiltration or convection. Insulation performance isalso reduced when the trapped air isdisplaced, which can happen throughcompression or moisture uptake.

Rigid foam insulation from Dow has aclosed-cell structure. The ability of air toinfiltrate and circulate is greatly reducedwithin the boards, and they resist compression and moisture. So thetrapped air stays trapped … and theinsulating value remains high.

A microscopic view of rigid foam insulation revealsthousands of closed cells that effectively trap air.

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Dow has designed productsthat fit a wide variety of roofingneeds. No matter what kind ofPMR application you haveplanned, we have an insulationproduct that fits the bill.

STYROFOAM™ ROOFMATE™

An extruded polystyrene foam insulation withdrainage channels on the bottom long edge. Provides excellent moisture resistance, durability and long-term R-value. Ideal for installation above waterproofing or roofingmembranes in PMR applications.

STYROFOAM™ Ribbed ROOFMATE™

An extruded polystyrene foam insulation boardwith 1/4" x 1/2" drainage channels on the bottom long edge of each board. Top surface of the board has ribs that form corrugations inthe long dimension of the board. Designed for installation above waterproofing or roofingmembranes in PMR applications that use pavers as ballast. Pavers can be installed directly over the ribbed foam surface withoutneeding pedestals.

STYROFOAM™ ROOFMATE™ DC (Canada only)A series of 1/2" x 1/2" grooves on the bottom ofthe board provide additional drainage on roofswhere little or no slope is present.

STYROFOAM™ PLAZAMATE™ (U.S. only)A high-density extruded polystyrene foam insulation board designed for installation abovewaterproofing or roofing membranes in mostplaza deck applications.

STYROFOAM™ Highload 40, 60, 100An extruded polystyrene foam insulation boardwith high compressive strength developedspecifically for in-ground application and freezerfloors. The products are also well-suited for plaza and protected membrane roofs that mustwithstand heavy traffic.

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow(1)Note: Not all products are available in all regions. Consult a Dow representative about product availability in your area.

STYROFOAM™ extruded poly-styrene insulation products forPMR are available in 2' x 8'and 2' x 4' boards. Nominalthicknesses range from 1" to4" (25 mm to 100 mm),depending on the product.

STYROFOAM™ Extruded Polystyrene Insulation Products Recommended for PMR Applications(1)

We Have the Ideal Productfor Your PMR Project

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Let the IndustryLeaders Help You Enjoy the Benefits of PMR

STYROFOAM™ extruded polystyrene insulation is crucialto the protected membraneroof. But a PMR requires morethan great insulation – andthat’s where Dow’s partnerscan help you. Dow works inconjunction with the topnames in the roofing industryto deliver the world’s best-performing roof.

We can help you design asolution that is just right foryour building. Call us today todiscuss PMR in greater detail.


A 30-year reusewarranty is available.Ask your Dowrepresentativefor details.


NOTICE: No freedom from any patent owned by Dow or others is to be inferred. Because useconditions and applicable laws may differ from one location to another and may change withtime, Customer is responsible for determining whether products and the information in thisdocument are appropriate for Customer’s use and for ensuring that Customer’s workplace anddisposal practices are in compliance with applicable laws and other government enactments.Dow assumes no obligation or liability for the information in this document. NOWARRANTIES ARE GIVEN; ALL IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESSFOR A PARTICULAR PURPOSE ARE EXPRESSLY EXCLUDED.

COMBUSTIBLE: Protect from high heat sources. Local building codes may require a protectiveor thermal barrier. For more information, consult MSDS, call Dow at 1-866-583-BLUE (2583)or contact your local building inspector. In an emergency, call 1-989-636-4400 in the U.S. or1-519-339-3711 in Canada.

Building and/or construction practices unrelated to building materials could greatly affect moistureand the potential for mold formation. No material supplier including Dow can give assurance thatmold will not develop in any specific system.

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of DowPrinted in U.S.A.

Form No. 179-05471X-0107P&M178-00254X-0107P&M

THE DOW CHEMICAL COMPANY • Building Solutions • 200 Larkin • Midland, MI 48674

FOR TECHNICAL INFORMATION: 1-866-583-BLUE (2583)

FOR SALES INFORMATION: 1-800-232-2436

DOW CHEMICAL CANADA INC. • Building Solutions • Suite 2200

250 – 6th Ave. SW • Calgary, AB 2TP 3H7

FOR TECHNICAL INFORMATION: 1-866-583-BLUE (2583) (English); 1-800-363-6210 (French)

FOR SALES INFORMATION: 1-800-232-2436 (English); 1-800-565-1255 (French)

www.dowbuildingsolutions.com

B U I L T O N S C I E N C E

STYROFOAM™ extruded polystyrene insulation from Dow is the only rigid insulation product built on the scientific expertise of The Dow Chemical Company, a leading global supplier of chemical, plastic and agricultural products and services.

Nearly 60 years ago, Dow pioneered STYROFOAMextruded polystyrene insulation, which revolutionizedinsulation science. Our commitment to innovation continues. Drawing on the vast research, developmentand technological resources of Dow and an openexchange of information with building professionals, STYROFOAM building products offer proven thermal envelope solutions for every application.


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