ASHRAE NY-08-021-2008 Residential Stucco Wall Assembly Moisture Performance Evaluation《住宅灰泥墙类湿度性能评估》.pdf

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1、156 2008 ASHRAE ABSTRACT This paper describes the results of laboratory experimentsusing insulated stucco wall assemblies representative of Cali-fornia new home construction practice to characterize thesusceptibility of targeted building assemblies to mold growthin the presence of moisture loading c

2、onditions. Experimentsinclude wall drying rates, propensity for mold growth, anddrainage capacity using unique test protocols tailored to meetexperiment goals. Experimental data provided evidence thatwalls with building paper and exterior polystyrene insulationdried more slowly than walls with house

3、wrap and no exteriorinsulation. Mold-resistant gypsum panels and sealer exhibitedsignificant resistance to mold growth, but only in treated areas.Mold growth in cellulose insulation was less than expected.Drainage capacities of assemblies with stucco adhered to theweep screed were much lower than wa

4、lls with full drainageflow channels. Additional laboratory evaluations as well asconsensus performance and prescriptive standards supportedby field data and validated models are recommended. INTRODUCTIONMold can grow almost anywhere, and requires only air,water, a food source, and moderate temperatu

5、res to thrive.Under the correct conditions, new mold growth can occur in aslittle as 48 hours. When water intrudes into envelope cavitiesin a sustained manner or does not dry quickly, mold may prop-agate due to trapped moisture. Damp conditions in envelopecavities and resulting mold growth compromis

6、e buildingenvelope energy efficiency, damage building materials, andaffect the health and productivity of susceptible occupants.Once mold growth occurs, it is costly to remove and can resultin expensive litigation. By understanding the buildingconstruction parameters affecting mold growth from bulkw

7、ater intrusion, it may be possible to mitigate or prevent moldgrowth, thereby limiting heating and cooling energy losses,reducing building remediation costs, and avoiding humanexposures.The Energy Efficient Mold-Resistant Building Assem-blies for California Homes program was a 30 month projectfunded

8、 by the California Energy Commission and GasResearch Institute to conduct a detailed investigation of resi-dential building construction practices and building assem-blies that may be resistant to mold formation and growth. Theproject team included six research organizations, two Califor-nia builder

9、s, 18 participating manufacturers, and a ProjectAdvisory Committee (PAC) comprising product manufactur-ers, building scientists, participating utilities, participatingbuilders, and state agencies. Based on the literature reviewconducted as a part of the project (Walker et al. 2004) and inputfrom Com

10、mission staff, the project team, PAC members, andbuilding industry experts, the highest value areas for this proj-ect to address with laboratory testing and field demonstrationswere water-resistive barrier (WRB) design options (especiallyaround windows), concrete slab installation practices andmater

11、ials (especially vapor retarder location and fill materi-als), and drying times for built up wall assemblies. Accordingto references in the literature review and input from PACmembers, components and subsystems have been testedextensively in the laboratory for mold growth and impact ofmoisture by bu

12、ilding scientists, universities, and manufactur-ers (see also Treschel 1994, Treschel 2001, and Rose 2005).Significant testing and analysis has been done on a variety ofbuilt-up wall assemblies, including stucco walls, especially inCanada (see CMHC 1999, Burnett 2001, CMHC 2001,Residential Stucco Wa

13、ll Assembly Moisture Performance EvaluationNeil P. Leslie, PEMember ASHRAENeil P. Leslie is a research manager in the End Use Solutions Sector at Gas Technology Institute, Des Plaines, IL.NY-08-0212008, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org).

14、 Published in ASHRAE Transactions, Volume 114, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.ASHRAE Transactions 157Hazleden et al. 2001, and Teasdale-St-Hilaire et al. 2

15、004).Additional testing was deemed to be valuable for completestucco wall assemblies commonly found in California. Thelaboratory investigations were intended to complementcomponent and subsystem testing to provide a better under-standing of the behavior of the entire stucco wall assembly andto colle

16、ct useful data on the performance of wall cavities andmaterials as a part of a complete assembly. These testsprovided empirical data using existing and newly developedtest protocols that were intended to permit replication by othertesting organizations and provide a technical basis for builderdesign

17、 recommendations. The project included laboratory and field studies of build-ing assemblies that are important to keeping building materi-als dry, and therefore free of mold growth (Leslie 2006a). Thispaper summarizes results of laboratory evaluations of WRBdesign alternatives in insulated stucco wa

18、ll construction(Leslie 2006b). OBJECTIVEThe objective of the laboratory studies was to perform asystematic evaluation of residential wall materials, assem-blies, and construction practices previously identified in aliterature review and expert interviews (Walker et al. 2004)and recommended for furth

19、er study by the PAC based on theirpotential for mold and moisture resistance. Laboratory evalu-ations focused on water drainage capacity at the WRB/wallinterface, wall drying rates, and propensity for mold growth inwall cavities and on surfaces. APPROACHSpecific laboratory tests and protocols were d

20、eveloped inconjunction with project team members, builders, PACmembers, sponsors, and industry consultants and summarizedin a laboratory evaluation test plan (Leslie 2004). The test planprovided the initial framework for laboratory evaluations ofwall assemblies. Based on experience gained during the

21、performance of laboratory evaluations, the project teamupdated test goals, protocols, facilities, and test matrix tomaximize the value of each experiment.Wall AssembliesTable 1 lists the wall assembly configurations evaluated inthese experiments. Wall assemblies (Figure 1) included three-coat stucco

22、 cladding, one-coat stucco cladding with exteriorinsulation, and EIFS cladding with drainage mat. Structuralframing options included open-frame construction andoriented strand board (OSB) sheathing. WRBs includedasphalt saturated building paper and non-perforated spun-bonded polyolefin housewrap. Wa

23、ll assembly dimensionswere selected based on input from the PAC and building scien-tists to provide manageable assemblies for experiments whilestill being large enough to obtain reasonably relevant infor-mation on targeted wall performance. Three-coat stucco walls included a scratch coat, browncoat,

24、 and finish coat of Portland cement plaster stucco withtotal cladding thickness of approximately 7/8 in. (22 mm)including the finish coat. One-coat stucco combined thescratch coat and brown coat into a single base coat of fiber-reinforced Portland cement plaster stucco 2/5 in. (10 mm)thick with tota

25、l cladding thickness of approximately in (13mm) including the finish coat. EIFS (also called syntheticstucco), typically proprietary formulations, included a poly-mer and cement base coat with total thickness of approxi-mately in (6 mm) including finish coat. All wall assemblieswith stucco cladding

26、included metal weep screeds at thebottom. The weep screed for the EIFS wall assembly was aplastic weep screed compatible with the other elements of theEIFS cladding. Table 1. Stucco Wall Assembly ComponentsBuilding Assembly DescriptionBaseline Stucco WallThree-coat stucco, two-ply grade D 60 minute

27、building paper over OSB sheathing, wood studs with kraft-faced R-13 fiberglass batt insulation, in (13 mm) gypsum panel, latex primer and finish coat- Open Frame Baseline with one-ply grade D 60 minute building paper, open frame- High/Low Drainage Openings Baseline with high/low drainage openings.-

28、Housewrap Baseline with 58 perm housewrap for inner layer- Textured Housewrap Baseline with 50 perm textured housewrap for inner layer- One-Coat, Insulated Sheathing Baseline with one-coat stucco, insulated sheathing- EIFS Baseline with EIFS instead of three-coat stucco- Cellulose Insulation Baselin

29、e with cellulose instead of fiberglass insulation- Anti-Microbial Gypsum Panel Baseline with anti-microbial gypsum panels- Fiberglass Gypsum Panel Baseline with fiberglass gypsum panels- Mold Resistant Sealer Baseline with mold-resistant sealer158 ASHRAE TransactionsFacilities and ApparatusAll wall

30、assembly evaluations were conducted in a 15 ft(4.6 m) high air conditioned laboratory in nearly still aircontrolled at 78F (25C). Test apparatus included:Two test stands with load cells for weight differentialmeasurements,Precision scales for gross wall and insulation weightsMoisture loading nozzle

31、and flow controller to injectwater into wall assemblies,Moisture content, relative humidity, and temperaturesensors, Infrared camera for surface temperature measurements,Sensor control and signal conditioning microprocessors, Data acquisition system to record and monitor data. The load cell test sta

32、nds were designed and constructed atthe laboratory to provide precise measurements of wall assem-bly weight (Figure 2). Each test stand included:Wood posts for pivot bearing, embedded in concretecasing, Pillow block pivot bearing and metal counterweight barwith counterweights,Compression load cell a

33、ttached to wood frame,Adjustable wall hanging clips for centering and verti-cally hanging wall assemblies,Data acquisition wiring harness and punchdown blockfor sensor wiring.Wall assemblies were hung from each fixture and coun-terweights added to provide approximately 5 lb (2.3 kg) netweight on the

34、 compression load cell (20 percent of full range)when dry. The automated data acquisition system (DAS) was asignal conditioning microprocessor and datalogger with two64 channel multiplexers, power supply, battery backup, andEthernet access. Software programs for signal conditioningand datalogging we

35、re written for each test sequence. Sensors included insulation temperature and relativehumidity, wood stud and OSB moisture content and tempera-ture, and room temperature and relative humidity. Tempera-ture and relative humidity sensors were thermistors and thinfilm capacitance sensors encased in 58

36、 perm water resistantsheathing. Resistance moisture pins and wood temperaturethermistors were specially designed and fabricated for thisproject. Data was collected once a minute, and hourly averageswere recorded to the file.Experiment CategoriesWall assembly laboratory evaluations involved three cat

37、e-gories of experiments, each with different protocols to achieveexperiment objectives: Susceptibility to Mold Growth,Wal Drying Rate,WRB Drainage Capacity.Protocols and instrumentation associated with theseexperiments took advantage of past efforts at other researchorganizations, but for the most p

38、art they were unique to thisproject to meet specific experiment goals. Figure 1 Stucco wall assembly construction for moisturemeasurement experiments.Figure 2 Wall weight load cell apparatus.ASHRAE Transactions 159Susceptibility to Mold Growth ProtocolsMold growth experimental protocols were designe

39、d toallow exploration of a number of hypotheses regarding moldformation and growth on wall assemblies, including:Mold growth occurs readily with a suitable food sourceand favorable environmental conditions, Water intrusion events in wall cavities provide favorableconditions for mold growth,Cellulose

40、 materials (wood, OSB, paper, insulation) pro-vide a suitable mold food source,Dirt or construction dust on fiberglass insulation pro-vides a suitable mold food source, Mold-resistant materials and coatings are effective atdelaying mold growth on treated areas or materials,Wall assemblies subjected

41、to significant water intrusionevents will not dry out quickly enough to avoid moldgrowth.Under the initial protocol for mold growth and wall dryingrate experiments, one pint ( l) of water was poured into eachof the two wall cavities through a hole drilled in the top studwith all edges sealed to char

42、acterize drying time toward theinterior and exterior wall surfaces. One pint ( l) water pourswere repeated at intervals based on wall cavity moisturecontent and relative humidity in an effort to provide long termrelative humidity and temperature conditions consideredconducive to mold formation and g

43、rowth. Solar effects weresimulated with three 250 watt infrared heat lamps for eight hourperiods per day. Heat lamps were placed approximately 2 ft(0.6 m) from the wall, with two heat lamps directed at thebottom half of the wall and the third directed at the top half ofthe wall. Rain effects were si

44、mulated using three flat-spraynozzles that wetted the stucco surface for 30 minutes per eventat a rate of approximately 1 gpm (3.8 lpm). This approach wasintended to permit both drying rate measurements and moldgrowth experiments to occur simultaneously and minimize thenumber of weeks necessary to p

45、erform each set of experiments.Based on interactions with PAC members and building scien-tists providing input to the team, it was expected that this exper-imental sequence would facilitate mold growth in susceptibleassemblies and provide reasonable data on drying rates.The initial mold growth and w

46、all drying rate protocolsfailed to differentiate component and wall assembly moldgrowth performance adequately. Nor did the protocols suffi-ciently control boundary layers for use with moisture transportmodels. The protocols were substantially modified based onconsultation with PAC members and build

47、ing scientists withexpertise in moisture loading and mold growth experiments. The revised protocols were designed to provide more suit-able conditions for significant mold growth and comparativedrying rates for the WRB options evaluated. For mold growthevaluations, the wall assemblies were fully enc

48、ased in plastic(three layers of shrink wrap) to maintain high moisture contentfor an extended period. For wall drying experiments, five ofthe six sides were encased in plastic taped to the assembly tobias vapor flow toward the WRB side. The revised protocolswere more successful in meeting experiment

49、 goals but areconsidered less representative of actual field conditions thanthe initial protocols. Figures 3 and 4 show sensor locations for all wall assem-blies except the mold-resistant sealer assembly. Moisture pinswere located in treated and untreated sections in that assembly.Figure 3 Moisture pins and thermistors installed in studsand OSB sheathing. Figure 4 Wall assembly DAS sensor locations.160 ASHRAE TransactionsFor mold-resistant gypsum panel experiments, R-19kraft-faced fiberglass insulation was compressed into the 3in (89 mm) cavity to increase initial water loading i