1、Designation: D7851 17Standard Guide forDesign of Sustainable, Low-Slope Roofing Systems1This standard is issued under the fixed designation D7851; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide provides guidance and considerations relatedto designing sustainable low-sloped roofing systems, includingexposed membrane roofs, m
3、embranes covered with vegetative(green) overburden systems, ballasted roofs, and protectedmembrane roofing assemblies. A sustainable roofing systemminimizes environmental impact, conserves energy, and hasmaximized service life.1.2 The primary purpose of a roofing system is to weather-proof the build
4、ings top surface. Implementing a sustainableroofing system is the intent of this guide.1.3 This guide acknowledges that many factors outside thedesigners control affect the longevity of a roofing system. Thedesigner may rely on industry literature (X1.1) and personalexperience with roofing systems t
5、o estimate the design life.1.4 The premise of this guide is to focus attention onenvironmental and other factors that may affect the roofingsystem over its service life. By considering these factors andincorporating into the roofing system design certain featuresthat mitigate these factors and their
6、 potential adverse effects onthe roofing system, the roofing system would be expected tohave a longer service life.1.5 This guide includes materials used in roofing systemsunder jurisdiction of ASTM Committee D08 on Roofing andWaterproofing. The applicability of this guide to other systemsand materi
7、als has not been determined.1.6 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations
8、prior to use.2. Referenced Documents2.1 ASTM Standards:2D1079 Terminology Relating to Roofing and Waterproofing3. Terminology3.1 GeneralTerms used in this guide are defined inTerminology D1079, except as defined below.3.2 Definitions:3.2.1 design lifethe planned period of time during whichthe roofin
9、g system is expected by its designer to reliablyperform its required functions, with minimal unplanned inter-vention.3.2.2 durabilitythe ability of the roofing system to per-form its required functions over a period of time within theenvironment for which it is designed and exposed.3.2.3 service lif
10、ethe period of time after installation dur-ing which a roofing system performs its required function(s)with minimal unplanned intervention.4. Summary of GuideNOTE 1The sustainable roofing system design process consists of thefollowing, sequential steps:4.1 Identification of Roofing System Demands, F
11、unctionalExpectations, and Site ConstraintsThe designer should de-termine factors, loads, and stresses that the roofing system mustwithstand as well as the impacts the roofing system may haveon the environment the building interacts with. These factorsapply limiting constraints for system and materi
12、al selection andthe associated installation process. There are also options forsustainable strategies and site and use constraints that willdefine the feasibility of sustainable strategies (for example,availability of sunlight for photovoltaic arrays).4.2 Determination of In-Service Performance Crit
13、eria andFunctional ExpectationsThe designer determines perfor-mance criteria and functional expectations of the roofing1This guide is under the jurisdiction of ASTM Committee D08 on Roofing andWaterproofing and is the direct responsibility of Subcommittee D08.24 on Sustain-ability.Current edition ap
14、proved Feb. 1, 2017. Published February 2017. DOI: 10.1520/D7158_D7158M-17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe
15、 ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelo
16、pment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1system in response to the in-service roofing system demands,functional options, and site constraints. Performance criteriainclude wind-uplift resistance an
17、d fire resistance.4.3 Identification of Candidate SystemsWith the criteriafor in-service performance and functional expectationsestablished, the designer can compile a list of candidatesystems that are capable of meeting the roof designrequirements, and are compatible with desired sustainablefeature
18、s and functional expectations.4.4 Evaluation of Candidate SystemsCandidate systemsare analyzed with respect to each other and with respect tocradle-to-grave (life-cycle) environmental impacts through anenvironmental life cycle assessment, component recyclability,minimization of waste, durability, an
19、d anticipated lifespan.4.5 Design of Optimal Best-Fit CandidateThe best-fitcandidate system is selected for final design.5. Significance and Use5.1 This guide is intended to help the user identify anddefine demands made upon the roofing system by factors suchas weather, climate, and building use, in
20、 light of the fact thatmany roofs are specified with secondary features that havequantifiable or non-quantifiable environmental or humanitarianbenefit such as alternative energy generation, vegetation, or useas open space. Awareness of the roofs use as a platform forthese secondary functions, as wel
21、l as the additional demandsthey make upon the roof, is needed to specify a durable andsustainable roof.5.2 It is the responsibility of the user of this guide todetermine the appropriate prescriptive requirements for imple-mentation of the sustainable roofing system based on consid-erations listed he
22、rein.5.3 Codes and local ordinances set minimum requirementsfor roofing systems. Nothing in this guide should be construedto abridge or lessen requirements of codes and local ordi-nances. Other entities, such as building insurers and systemmanufacturers, may have requirements for the roofing system.
23、5.4 Sustainability of a roofing system is site and usespecific. A roofing system considered sustainable for a certainsite or application may not be sustainable in a differentapplication. There may also be more than one roofing systemthat achieves an optimal level of sustainability for a given sitean
24、d application.5.5 Above-roof vegetative (green) systems and rooftopenergy generation systems are discussed herein because theyare frequently placed on roofs to reduce the buildings overallenvironmental impact. These features do not generally contrib-ute to the durability or longevity of the roof. Th
25、ese featuresmay be detrimental to roof system performance and impair theroofs ability to perform its primary function of protecting thebuilding if their impact is not accounted for in the roof design.5.6 Design of above-roof systems is beyond the scope ofthis guide; however, consideration of their p
26、otential impacts isoutlined herein.6. ProcedureNOTE 2The design process includes the following tasks, shared withprudent design of any roofing system but are included for completeness.An illustrative flow chart is provided in Appendix X2.6.1 Define Roofing System Demands, FunctionalExpectations, End
27、 User Requirements, and Site ConstraintsThe sustainable roofing design process begins by determiningand analyzing factors including, but not limited to: environ-mental and mechanical stresses that the roofing system will besubjected to, required functions and the uses of the roof,sensitivity of loca
28、l environment to the effects of the roofingsystem, interaction of the roof with the indoor buildingenvironment, building use and design life, and site factors thatmay affect selection of various sustainable roofing strategies.Some of these factors may be specified by local building codesand ordinanc
29、es but others will require determination on the partof the building and roofing system designers. To some degreethe various constraints, demands, and expectations may over-lap or may fall into more than one category. A partial list ofsuch considerations includes the following:6.1.1 Roofing System De
30、mands-Code Driven:6.1.1.1 Wind Velocity and Exposure,6.1.1.2 Fire Risk,6.1.1.3 Snow Loads,6.1.1.4 Live Loads,6.1.1.5 Roof Solar Reflectance and Thermal Emittance,6.1.1.6 Hail Exposure,6.1.1.7 Rainfall Rate, and6.1.1.8 Thermal Loads/Stress.6.1.2 Serviceability Considerations:6.1.2.1 Long-Term Weather
31、 Resistance,6.1.2.2 Foot Traffic/In-Service Abuse Level,6.1.2.3 Chemical Exposure,6.1.2.4 Building Design Life, and6.1.2.5 Indoor Humidification/Building Pressurization.6.1.3 End User Requirements:6.1.3.1 Platform for Energy Generation System,6.1.3.2 Platform for Vegetation,6.1.3.3 Use by People/Pla
32、nned Habitat for Wildlife, and6.1.3.4 Enhanced Thermal Efficiency.6.1.4 Site Considerations:6.1.4.1 Building Use,6.1.4.2 Surface Water Runoff Restrictions, and6.1.4.3 Building Orientation/Latitude/Availability of Sun-light.6.2 Determine Required Physical Properties and Perfor-mance CriteriaA sustain
33、able roofing system satisfies theminimum design requirements defined by codes andordinances, as well as the functional expectations and accom-modate site constraints developed in 6.1. Functional expecta-tions may not be dictated by applicable codes. Some functionsare demanded by the end user. Some a
34、re determined by theroofing system designer. Some functional expectations, such asthe roofs resistance to rooftop traffic, pollutants, and chemicalattack, affect durability and serviceability of the roof. Anotherset of criteria limits the roofs interaction with the localenvironment and establishes f
35、easibility of various sustainableroofing options. Some of these criteria, such as surfaceD7851 172reflectance, may be prescribed by local ordinance. Othercriteria are not required to meet minimum requirements and aredifficult to quantify. Establishing these criteria or featuresshould be based on a r
36、easonable or qualitative determination ofbenefit in mitigating the overall impact of the building and itsoccupants on the environment. These criteria can includerestoring vegetation displaced by the building footprint throughuse of rooftop plantings, runoff retention, or making availableroofing spac
37、e for alternative energy generation. Examples ofperformance criteria and functional concepts that addresssystem demands, functional expectations, and site constraintsinclude the following:6.2.1 Physical Properties and Performance Criteria to beDetermined:6.2.1.1 Wind Uplift Resistance,6.2.1.2 Fire R
38、esistance,6.2.1.3 Deck Structural Capacity,6.2.1.4 Resistance to Heat and UV Exposure,6.2.1.5 High Indoor Humidity/Building Pressurization,6.2.1.6 Hail Resistance Rating,6.2.1.7 Drainage and Slope Requirements,6.2.1.8 Foot Traffic Resistance,6.2.1.9 Chemical Resistance,6.2.1.10 Required Roof Service
39、 Life (should be greater thandesign life of above-roof components),6.2.1.11 Resistance to Potential Rooftop Uses, Vegetation,and Landscaping Activities (if applicable), and6.2.1.12 Potential for Moisture Accumulation Within theRoofing Assembly (considering wintertime membrane tem-perature based clim
40、ate, roofing emissivity and reflectance,indoor environment, and presence of vapor and air barriers).6.2.2 Additional Considerations for Durability andMaintainabilityGiven all other considerations of the lifecycle analysis and in-service performance being equal, adurable roofing system, one with grea
41、ter longevity or extend-able service life through minor (that is, low environmentalimpact) maintenance will use fewer resources, have lowerenvironmental impact and will therefore be more sustainablethan a roofing system that requires more-frequent replacement.The roofing system should incorporate fe
42、atures recognized asimproving the system durability by addressing local environ-mental stresses and building function as described above. Thedesign should use materials and incorporate features that havebeen proven over time to provide durable performance andreduce the quantity of components that re
43、quire maintenance infavor of low-maintenance or maintenance-free components.For many roof conditions, there exist detailing options withdiffering degrees of required maintenance and reliability.6.2.2.1 Roofing TerminationsThe design should minimizereliance on sealant at roofing membrane terminations
44、 at wallsand parapets. Roofing terminations immediately below cavitywalls or drainage type walls, including but not limited toportland cement plaster (stucco), brick masonry veneer orpanelized rainscreen-type wall systems should be protectedfrom water entry behind the roofing termination with a slop
45、ed,watertight flashing at the base of the wall. Similarly, roofingterminations below fenestration sills and door thresholdsshould be protected with a positively sloped, watertight sillflashing extending beneath the fenestration or door threshold.Edge securement should be specified and detailed to re
46、sistdesign wind loads.6.2.2.2 DrainagePositive slope to the primary drains,scuppers, or gutters should be provided for all roofing systemsso that standing water does not remain on the roofing mem-brane 48 hours after rainfall, when the roof is subjected toambient drying conditions.6.2.2.3 Penetratio
47、ns are unavoidable but should be mini-mized. Penetration pockets should be minimized because theytypically require more maintenance and pose a higher risk ofleakage than durable flashings. In the case of multiple small-diameter penetrating members, such as electrical conduit orrefrigerant lines, it
48、is often preferable to house them in aflashed enclosure that extends above the roof surface, wherethe penetrating elements can exit through protected openings inthe side of the enclosure.6.2.2.4 Air Barrier SystemSubstantial energy loss,condensation, and resulting damage to roofing components canbe
49、caused by infiltration or exfiltration of air through theroofing assembly or roof perimeter conditions. An independentair barrier system to prevent movement of extraneous air andmoisture into the roofing system should be considered forbuildings with high potential or design humidity and wherepressure differentials that may drive indoor air into the roofingsystem may exist.6.2.2.5 Leak DetectionWater leakage through roofingmembranes causes premature deterioration. Early detection ofleakage can prolong the service life of the roofing system.Leakage into roofing
