1、Designation: E 241 08Standard Guide forLimiting Water-Induced Damage to Buildings1This standard is issued under the fixed designation E 241; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in par
2、entheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide concerns building design, construction, com-missioning, operation, and maintenance.1.2 This guide addresses the need for systematic evalu
3、ationof factors that can result in moisture-induced damage to abuilding or its components. Although of great potential impor-tance, serviceability issues which are often, but not necessarily,related to physical damage of the building or its components(for example, indoor air quality or electrical sa
4、fety) are notdirectly addressed in this guide.1.3 The emphasis of this guide is on low-rise buildings.Portions of this guide; in particular Sections 5, 6, and 7; mayalso be applicable to high-rise buildings.1.4 This guide is not intended for direct use in codes andspecifications. It does not attempt
5、 to prescribe acceptable limitsof damage. Buildings intended for different uses may havedifferent service life expectancies, and expected service livesof different components within a given building often differ.Furthermore, some building owners may be satisfied withsubstantially shorter service lif
6、e expectancies of buildingcomponents or of the entire building than other buildingowners. Lastly, the level of damage that renders a componentunserviceable may vary with the type of component, the degreeto which failure of the component is critical (for example,whether failure constitutes a life-saf
7、ety hazard), and the judge-ment (that is, tolerance for damage) of the building owner. Forthe reasons stated in this paragraph, prescribing limits ofdamage would require listing many pages of exceptions andqualifiers and is beyond the scope of this guide.1.5 This standard does not purport to address
8、 the safetyconcerns associated with its use. It is the responsibility of theuser of this standard to establish appropriate safety and healthpractices and determine the applicability of regulatory limita-tions prior to use.2. Referenced Documents2.1 ASTM Standards:2C 168 Terminology Relating to Therm
9、al InsulationC 717 Terminology of Building Seals and SealantsC 755 Practice for Selection of Water Vapor Retarders forThermal InsulationC 1193 Guide for Use of Joint SealantsD 1079 Terminology Relating to Roofing and Waterproof-ingE 331 Test Method for Water Penetration of Exterior Win-dows, Skyligh
10、ts, Doors, and Curtain Walls by UniformStatic Air Pressure DifferenceE 547 Test Method for Water Penetration of Exterior Win-dows, Skylights, Doors, and Curtain Walls by Cyclic StaticAir Pressure DifferenceE 631 Terminology of Building ConstructionsE 632 Practice for Developing Accelerated Tests to
11、AidPrediction of the Service Life of Building Components andMaterialsE 1105 Test Method for Field Determination of WaterPenetration of Installed Exterior Windows, Skylights,Doors, and Curtain Walls, by Uniform or Cyclic Static AirPressure DifferenceE 1643 Practice for Installation of Water Vapor Ret
12、ardersUsed in Contact with Earth or Granular Fill Under Con-crete SlabsE 1677 Specification for an Air Barrier (AB) Material orSystem for Low-Rise Framed Building WallsE 1745 Specification for Plastic Water Vapor RetardersUsed in Contact with Soil or Granular Fill under ConcreteSlabsE2112 Practice f
13、or Installation of Exterior Windows, Doorsand SkylightsE 2136 Guide for Specifying and Evaluating Performanceof Single Family Attached and Detached DwellingsDurability2.2 Other Documents:ASCE/SEI 2405 Flood Resistant Design and Construc-tion, American Society of Civil Engineers, Structural1This guid
14、e is under the jurisdiction of ASTM Committee E06 on Performanceof Buildings and is the direct responsibility of Subcommittee E06.41 onAir Leakageand Ventilation PerformanceCurrent edition approved June 1, 2008. Published July 2008. Originally approvedin 1964. Last previous edition approved in 2004
15、as E 241 04.2For 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 ASTM website.1Copyright ASTM International, 100 Barr Harbor Dr
16、ive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Engineering Institute, Reston, VA.ASHRAE Handbook of Fundamentals Chapter 23: Thermaland Moisture Control in Insulated AssembliesFundamentals; Chapter 24: Thermal and Moisture Con-trol in Insulated AssembliesApplications; Chapter 27:V
17、entilation and Infiltration; Chapter 29: Residential Cool-ing and Heating Load Calculations; Chapter 30: Nonresi-dential Cooling and Heating Load Calculations; Ameri-can Society of Heating Refrigerating, and AirConditioning Engineers; Atlanta, GA, 2005.ASHRAE Standard 62 Ventilation for Acceptable I
18、ndoorAir Quality3ASHRAE Technical Data Bulletin, Vol 10, No. 3 Recom-mended Practices for Controlling Moisture in CrawlSpaces, American Society of Heating, Refrigerating andAir Conditioning Engineers, Atlanta, GA, 1994.ASTM MNL 18 Trechsel, H., (ed.), Moisture Control inBuildings, American Society f
19、or Testing and Materials,West Conshohocken, PA, 1994.ASTM MNL 40 Trechsel, H., (ed.), Moisture Analysis andCondensation Control in Building Envelopes, AmericanSociety for Testing and Materials, West Conshohocken,PA, 2001.Bateman, R., “Nail-On Windows” Installation (2) movement of water vapor by airm
20、ovement; and (3) water vapor diffusion by vapor pressuredifferences. These transport mechanisms can deliver moistureinto the building or the building envelope, in which cases it isdesirable that they be controlled. These transport mechanismscan also act to remove moisture from the building or buildi
21、ngenvelope, in which cases they may be used to promote drying.5.3.1 In control of moisture delivery to the building orbuilding envelope, the transport mechanisms that have thepotential for moving the greatest amounts of moisture should(where practical) be controlled first. In promotion of drying oft
22、he building or building envelope, the transport mechanismsthat have the potential for moving the greatest amounts ofmoisture should (where practical) be utilized first.5.4 Building assemblies can become wet in three ways: (1)moisture can enter from the exterior, (2) moisture can enterfrom the interi
23、or, or (3) the assembly can start out wet as aresult of using wet building materials or building under wetconditions.5.4.1 Moisture typically enters building assemblies from theexterior through three mechanisms: (1) liquid flow by gravity,air pressure, surface tension, momentum, or capillary suction
24、;(2) movement of water vapor by air movement; or (3) watervapor diffusion by vapor pressure differences.E2410845.4.2 Moisture typically enters building assemblies from theinterior through two mechanisms: (1) movement of watervapor by air movement, or (2) water vapor diffusion by vaporpressure differ
25、ences.5.4.3 Operation of mechanical equipment has not alwaysbeen recognized for its potential influence on moisture transfer.This potential influence should not be overlooked. Mostnotably, air handling equipment can induce a moisture trans-port mechanism that is capable of moving large amounts ofmoi
26、sture, namely movement of water vapor by air movement.Unplanned pressurization or depressurization of buildings orportions of buildings by air handlers can result in substantialmoisture accumulations in the building envelope.5.5 Moisture can typically be removed (dried) to the exte-rior or the inter
27、ior by three mechanisms: (1) liquid flow bygravity (drainage) or capillary suction, (2) movement of watervapor by air movement (ventilation), or (3) water vapordiffusion by vapor pressure differences.5.5.1 Where condensation of water vapor or water leaks canoccur, weep paths to drain liquid water to
28、 a place where it canbe dissipated are often effective. Converting liquid water tovapor, and dissipating the vapor by air movement may also bepractical.6. Limit States6.1 Identification of conditions that must be avoided inorder to prevent degradation of building components is animportant step in ma
29、king design or operating decisions. How-ever, precise guidelines for identification of such conditions aregenerally lacking. Rather rough estimates based on empiricalexperience are often used.6.2 Time and temperature are factors that are interrelatedwith moisture level in the degradation of building
30、 components.The moisture/temperature/time combinations that result inmaterial degradation furthermore vary with the type of mate-rial. For example, wood will not decay, even at elevatedmoisture content when its temperature is near or belowfreezing, and even at temperature conditions conducive todeca
31、y, wood can withstand intermittent wettings of shortduration to elevated moisture contents without decay becomingestablished. Conversely, masonry units can generally be ex-pected to withstand elevated moisture conditions at tempera-tures above freezing for extended time periods (conditionsunder whic
32、h wood decay might be expected), but sufferdamage if frozen in a saturated condition.6.2.1 Many materials or constructions have threshold watercontents below which deterioration may be slow enough to benegligible for designed life expectancy. As indicated in 6.1these threshold values are often rathe
33、r rough estimates. See“Humidity and Building Materials” (Connolly, 1993) forestimates.6.2.2 The concepts of critical moisture content and criticalcumulative exposure time (see 3.5.5) are discussed in Chapter26 of ASTM MNL 18. Although these concepts are generallyrecognized by building scientists, or
34、ganized use of these aslimit states by designers has not yet become a well-recognizedpractice.6.3 Alimit state is frequently based on avoidance of damageto a component as the result of its getting wet.Alimit state mayalso be based on avoidance of damage to a component as aresult of moisture conditio
35、ns in an adjacent component. Forexample, limiting moisture-induced dimensional change ofplywood sheathing may be critical to prevent cracking ofstucco cladding.7. Design Evaluation Tools7.1 Means for evaluating the design of building envelopesfrom the perspective of moisture management can be classi
36、fiedas follows: (1) conceptual, (2) mathematical using computersimulation models, and (3) mathematical using calculationsthat can be performed without computer software (sometimesreferred to as manual design tools).7.1.1 Conceptual Design EvaluationThis approach in-volves the following three-step pr
37、ocedure: (1) determine prob-able external and internal environmental loads (determineclimate and interior design conditions), (2) determine thepotential moisture transport mechanisms in each assembly, and(3) select moisture control strategies. This approach provides aqualitative perception of how a
38、building will perform under theinfluence of all the moisture loads the building is likely to besubjected to. The Moisture Control Handbook (Lstiburek andCarmody, 1991) provides a more comprehensive treatment ofthis approach. Conceptual design evaluation can be used toselect a construction for a give
39、n climate, as well as to evaluatehow a proposed construction may perform in a given climate.7.1.2 Computer Hygrothermal Analysis SimulationModelsThese models have been developed to quantitativelypredict moisture and temperature conditions within proposedassemblies using boundary conditions represent
40、ative for theclimate and interior design conditions. As stated in Chapter 6of ASTM MNL 40, the more detailed computer simulationmodels employ finite-element or finite-difference schemes.These models mathematically model moisture and heat transfermechanisms at the inner and outer surfaces of the asse
41、mbliesand within the assemblies. Some of the models predict mois-ture transfer by air movement and liquid water flow as well asby vapor diffusion. Use of such models requires knowledge ofbuilding physics and of the limitations of the model used. Mostmodels allow estimates of the duration of a set of
42、 temperatureand moisture conditions within assemblies. A discussion ofavailable models is found in Chapter 2 of ASTM MNL 18,inChapter 6 of ASTM MNL 40, and in Chapter 23 of theASHRAE Handbook of Fundamentals.7.1.3 Manual Design ToolsThese are termed “simplifiedhygrothermal analysis method models” in
43、 Chapter 6 of AST-M MNL 40 and “simplified hygrothermal design calculationsand analyses” in Chapter 23 of the ASHRAE Handbook ofFundamentals. Manual design tools, like computer simulationmodels, provide quantitative estimates of moisture conditionswithin building envelopes. They only account however
44、 formoisture transfer by vapor diffusion. Their focus is on predict-ing the occurrence of sustained condensation within buildingassemblies. The calculations for manual design tools can beeasily performed with a handheld calculator or in a computerspreadsheet. The traditional design tool used in Nort
45、h Americais a manual design tool and is referred to as the dewpointmethod. An example of the dewpoint method is outlined inAppendix X1.1 of Practice C 755. The validity and usefulnessE241085of predictions made with manual design tools have limitations.Most notably, manual design tools do not provide
46、 estimates ofthe time period during which potentially damaging conditionsmay occur. Despite the limitations of manual design tools,some relatively unsophisticated analysis procedures, like dew-point analysis, can be useful for rapidly comparing relativeperformances of many different proposed constru
47、ctions. Adiscussion of manual design tools is found in Chapter 11 ofASTM MNL 18 and in Chapter 23 of the ASHRAE Handbookof Fundamentals.8. Examples of Practices that Enhance Durability8.1 Drainage of Precipitation and Surface Runoff:8.1.1 Surface GradingGround should slope away fromwalls so that pre
48、cipitation runoff from land areas does not pondnear the foundation.8.1.2 Building External DrainsDischarge from drains atground level should be carried away from the foundation, andshould flow away from it.8.1.3 Below-Grade Drainage SystemsIn some casesbelow-grade drainage systems may be required. I
49、n some cases,dissipation of collected water by pumping will be required.Below grade drainage systems are discussed in Chapter 2 ofThe Moisture Control Handbook (Lstiburek and Carmody,1991).8.2 Limiting Intrusion of Precipitation:8.2.1 Precipitation has the potential for delivering excep-tionally large moisture loads to buildings, and is usually thelargest potential moisture source (see Chapter 8 of ASTM-MNL 18). It is imperative that this source be controlled,specifically that precipitation be excluded from the buildingenvelope. In some cases, entry of limited mounts of pr
