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HomeMy WebLinkAboutDOC-1994-Moisture Control in Buildings - 05/01/00 MON 12:01 FAX 360 956 2217 WSU Energy Olympia [a 010 as'a9 l i RECEIVED DEC 2 81994 WSEO LIBRARY Moisture Control in Buildings. Heinz R. Trechsel, Editor LIBRARY WASHNGTON STATE ENERGY OFFICE 925 EL 1'.1 ST. SE, BLDG.4 PO WX 4310 OLYMPIA WA 985043169 ASTM Manual Series:MN1, 18 ASTM Publication Code Number(PCN) 28.018094-10 Qy l 1916 Race Street m Philadelphia,PA 19103 i 05/01/00 MON 12:01 FAX 360 956 2217 WSU Energy Olympia foil 332 MANUAL ON MOIST U CONTROL IN BUILDINGS is controlled by providi g an air seal(air retarder)at either HEATING CLIMATF WALL CONSTRUCTION, the interior or exteri of the wall. This is facilitated in this VINYL/ALUMINUM SIDING, IMPERMEABLE wall assembly by e' er sealing the interior gypsum wall SHEATHING(FIG. 5) board or polyethy ne vapor diffusion retarder to the wall Framing or by sea ng the exterior sheathing to the wall fram- Rain ing. This air s ling can be accomplished with adhesive, Rain penetration in this wall assembly is controlled by the caulk, oz so other sealant, An exterior air seal at the asphalt-impr aced fiberboard sheathing in this example application of the rain screen principle. also Cacilila s pressure equalization of the exterior cladding. Rain Absorption/CapillarySuction Exterior ai seals are typically accomplished in this example an by installi a continuous exterior building paper(vapor per- Rain absorption by the vinyl or aluminum siding and siding mea6le a nonabsorptive is desirable). capillarity effects are not a concern in this wall assembly as a result of the inherent material properties of the vinyl and Vapor DI uslon aluminum- A building paper, installed only to protect the impermeable rigid insulation from water absorption, is not Vapor ion from the interior du ng heating periods e- required in this assembly For the same reason, . controlled by i tolling a vapor dill-us" n retarder at the inte- rior of the wall. this example, a ntinuous polyethylene Air Movement sheet is installed bet een the intcri r gypsum board and the wall framing and acts he vapor illusion retarder. Air-transported moisture from the interior(exfiltration of Vapor diffusion from a exte or in this wall assembly warm moisture-laden intcrior air during the heating season) during cooling periods (an un er the action of incident is controlled by providing an air seal (air retarder)at either solar radiation) is controlled y - stalling a vapor diffusion the interior or exterior of the wall. retarder at the imerior of thew I ssembly between the wall framing and the interior gypsum oard-Although installing a Vapor Diffusion vapor diffusion retarder at this I ation in this climate does not prevent moisture move me t by vapor difftisian from Vapor diffusion from the interior during heating periods is entering the wall,the vapor di itnrctardereffectivelypro- controlled by installing a vapor diffusion retarder at the intc- sects the interior gypsum board red ny interior finishes from rior of the wall. moisture damage.This interi vap r diffusion retarder can Accumulation of moisture within the wall assembly trans- getwetonthecavitysidedu ngthe yas a result of exterior- ported by vapor diffusion from the interior during heating absorbed moisture in the rick venec riven inward by inei- periods is also controlled by elevating the temperature of the dent solar radiation d the air-con ioned interior. This first condensing surface within the wall assembly,namelythe moisture then typi ly migrates ou rd in the evening cavity side of the exterior sheathing.This is accomplished in when the temper re gradient reverses, his wall assembly this example by installing an insulating sheathing which lim- in this clitnate c get intermittently wet fr m the exterior as its periods of potential condensation. well as dry int rmiucntly to the exterior,Si ce intermittent wetting of vapor diffusion retarder met occur fit this Comments assembly,th interforvapor diffusion retartic houldbe con- In this wall assembly,drying towards either the interior or tinuous to provide satisfactory performanc . Foil-backed exterior is limited by virtue of the installation of a vapor- interior sum board may not be effective d e to disconti- nuities at j 'nts.Foil-backed cavity insulation so may not be effective F the same reason. A continuo polyethylene vapordiffus nremrdcrhas proven robe effe tiveinthistype of assembly. t VINYL OR ALUMINUM SIDING Comments ,\ IMPERMEABLE RIGID INSULATION Wall drying tt>~,v.ards the exterior' this wall assembly is CAVITY INSULATION IN Facilitated by installing a vapar-pe sable sheathing on the WOOD FRAME WALL _ exterior of the wail framing alon ith an air space between 6-MIL POLYETHYLENE VAPOR the cladding(bricl&eneer),the cathing to act as a receptor DIFFUSION RETARDER/AIR RETARDER(CONTINUOUS AND for interior cavity,moisture Should the wall assembly SEALED AT ALL PENETRATIONS) become wet during'service be built initially wet through the use of Framing mate sorrhe use ofwet-appliedcav GYPSUM BOARD WITH ANY i[y insulations(wet spray,ce ulose or blown fiberglass),it can PAINT OR WALL COVERING dry to the as(wet into the -r space behind the brick veneer during the heating season r daring evenings. Either vapor-permvabl or vaponimpermeable surface fin. FIG$—Heating climate wall construction—vinyl/aluminum siti• I. ishes may be used in co unction with this wall assembly, ing with impermeable sheathing. i I, 05/01/00 MON 12:02 FAX 360 956 2217 WSU Energy Olympia [a012 WN II CHAPTER 17—MOISTURE CONTROL,FOR NEW RESIDENTIAL BUILDINGS 333 �� l r impermeable exterior sheathing and an interior vapor diffu- the interior(exfiltration of warm,moisture-laden interior air sion retarder• during the heating season) is controlled by providing an air If the wall assembly is built initially wet through the use of seal(air retarder)at eithcrthe interior or exteriorof the wall. ! wet harming materials or the use of wct-applied cavity insu- lations i wet spray cellulose or blown fiberglass),it may not dry.Act ordingly,dry Framing materials(wood at a moisture Vapor Diffusion content of 19% by weight or lower) and dry-applied insula- Vapor diffusion from the cxteriorin this wall assembly dur- be alons an a recommended; e alternatively,wall assemblies must ing cooling periods is controlled by installing a vapor diffu• be allowed to dry prior el enclosure, Sion retarder at the interior of the wall assembly between the Interior moisture levels should he limitedto35%relative wallframingandtheinteriorgypsumboard.Althoughinstall- ' humidin:at 70`F (21.1°C) during heating periods to further ing a vapor diffusion retarder at this location in this climate facilitate the control of air-transported moisture and vapordif• does not prevent moisture movement by vapor diffusion from fusion w i th this wall assembly since only limited drying of the assembbr occurs, entering the wall from the exterior, dte vapor diffusion Either vapor-permeable or vapor-impermeable surface fin• retarder effectively protects the interior gypsum board and ishes may be used in conjunction with this wall assembly. any interior finishes from moisture damage as well as reduc- ingthe latent cooling load of the structure.This interiorvapor I� diffusionretardercangetweton the cavitysideduringtheday MIXEID CLIMATE WALL CONSTRUCTION, as a result of exterior-absorbed moisture in the fiberboard or VINYI:/ALUMINUM SIDING, PERMEABLE gypsum sheathing drive inward by incident solar radiation. SHEA-THING(FIG.6) This moisture then typically migrates outward in the evening when the temperature gradient reverses.This wall assembly Rain in this climate can get intermittently wet from the exterior as well as dry intermittently to the exterior.Since intermittent Rain penetration in this wall assembly is controlled by the wetting of the vapor diffusion retarder may occur in this applican on of the rain screen principle. assembly,this interior vapor diffusion retarder should be con- tinuous to provide satisfactory performance. Foil-backed q Rain Ahsor'ption/Capillary Suction interiorgypsum board may not be sufficiently effective due to 6 discontinuities atjoints.Foil-back insulation bans may not be Rain absorption by the exterior asphalt-impregnated fiber- effective for the same reason- A continuous polyethylene board or gypsum sheathing and capillarity effects arc vapor diffusion retarder has proven to be effective in this type it controlh•d by the installation of a building paper. In this ofassembly- assembli,, a vapor-permeable, nonabsorptive building paper Vapor diffusion from the interior during heating periods is is desiral,lc, controlled by installing a vapor diffusion retarder at the intc- rior of the wall.In this example,a continuous polyethylene Air Movement sheet is installed between the interior gypsum board and the wall framing and acts as the vapor diffusion retarder. Air-transported moisture from either the exterior(infiltra- !' Lion of warm, humid air during the cooling season)or from - q: Comments I i VINYL OR ALUMINUM SIDING In this wall assembly,drying towards the exterior through I. a the vapor-permeable exterior sheathing (asphalt-impreg- BUILDING PAPER nated fiberboard or gypsum board) occurs but is limited ASPHALT IMPREGNATED somewhat by the installation of a vapor-impermcable exte. FIBERB0,IRD OR GYPSUM rior cladding(vinyl or aluminum siding).Drying towards the SHEATHING(PERMEABLE) interior is limited by virtue of the installation of an interior CAVITY INSULATION IN ) vapor diffusion retarder. Should the wall assembly become WOOD FRAME WALL wet during service or be built initially wet through the use of 6-MIL POL YETHVLENE VAPOR wet Framing materials or the use of wct-applied cavity insu- DIFFUS1014 RETARDER lations (wet spray cellulose or blown fiberglass), the all assembly will dry to the exterior.However,the rate of drying GYPSUM WARD COVERIWITH NG may not be sufficient to prevent the occurrence of problems.PAINT OR WALL COVERING Y Local experience may provide guidance. In the absence of ONS OLr P SEALANT prior experience or local historical experience. it may be ON SOLE PLATE INTERIOR desirable to use dry framing materials (wood at a moisture LIMITED DRYING content of 19%by weight or lower) and dry-applied insula- TO EXTERIOR tions.Alternatively,wall assemblies could be allowed to dry prior to enclosure- FIG.6-111lixed climate wall construction—vinyl/aluminum siding Either vapor•permeable or vapor-impermeable surface fin- with permeable sheathing. ishes may be used in conjunction with this wall assembly. it I ;Ir 05/01/00 MON 12:04 FAX 360 956 2217 WSLI Energy Olympia RJ013 < �f 334 MANUAL ONMOISTURE CONTROL INBUILDINGS MIXED CLIMATE WALL CONSTRUCTION, ity side of the exterior sheathing.This is accomplished in this VINYL/ALUMINUM SIDING,IMPERMEABLE example by installing an insulating sheathing of sufficient SHEATHING FIG,7 thermal resistance to limit periods of potential condensation to acceptable levels.An acceptable period of potential con. Rain to would be a period sufficiently brief that does not Rain penetration in this wall assembly is controlled by the allow wood decay to commence or interior surface water application of the rain semen principle. stain marks or mold or mildew to appear, The period of potential condensation of a wall assembly is determined by i, the temperature of the first condensing surface and the inte- Rafn Absorptlon/Capillary Suction rior moisture level.The temperature of the first condensing Rain absorption by the vinyl oraluminum siding andsiding surface during the heating period in this wall assembly is capillarity effects are not a concern in this wall assembly as a determined by the ratio of the amount of thermal insulation result of the inherent material properties of the vinyl and installed to the exterior ofthe condensing surface compared aluminum. A building paper, installed only to protect the to the amount of thermal insulation installed to the interior impermeable rigid insulation from water absorption, is not of the condensing surface.For this wall assembly in this cli- required in this assembly for the same reason, mate zone, the thermal resistance of insulating sheathings should be R-7 or greater,and the thermal resistance of cavity insulation should be R-11 or less,where an interiorvapor dif- Alr Movement fusion retarder is not utilized.Furthermore,interiormoisturc Air-transported moisture from either the exterior(infiltra- levels during hearing periods should be limited to 45%rela- tion of warm humid air during the cooling season) or from tive humidityat 70-F(21.1°C)(I21. the interior(exfiltration of warm moisture laden interior air during the heating season) is controlled by providing an air Comments seal(air retarder)at either Lhc interior or exterior of the wall. Wall drying towards the interior in this wall assembly is facilitated by installing avapor-permeable paint finish on the Vapor Diffusion interior gypsum wall board. Should the wall assembly Vapor diffusion from the cxteriorduring cooling periods is become wet during service or be built initially wet through controlled by installing a vapor diffusion retarder on the exit- the use of wet framing materials or the use ofweo-appliedcav- II rlor of the wall. In this example-an impermeable rigid insu- try insulations(wet spray cellulose orblown fiberglass),it can .i lation is installed as the exteriorwall shcathingand acts as the dry to the interior due to an inward temperature and vapor I exterior vapor diffusion retarder. pressure gradient present as a result of air conditioning the Accumulation of moisture within the wall assembly trans- enclosure during the cooling season and ambient climatic ported by vapor diffusion from the interior during heating conditions during the spring and fall. periods is controlled by elevating the temperature of the first Interior moisture levels should be limited to 45%relative condensing surface within the wall assembly,namely the cav- humidity at 70°F(21,1°C) during heating periods to further j facilitate the control of air-transported moisture and vapor dif- fusion with this wall assembly since limited drying of the CAULKING OR SEALANT assembly can only occur to the interior. ON TOP PLATE The facing material on faced cavity insulations installed (EXTERIOR OR INTERIOR) with the facing towards the interior of the wall in this climate VINYL OR ALUMINUM SIDING can serve to retard drying to the interior.Faced cavity insu- lations can be installed where drying to the interior is not R-7 MIN. IMPERMEABLE required, or, alternatively, the cavity insulation can be RIGID INSULATION installed with the facing material towards the outside of the 3-1/2-IN, (R-11))CAVITY INSULATION 14 cavity, IN 2 k 4 WOOD FRAME WALL The facing material an faced cavity insulations installed with the facing towards the interior of the wall in this wall GYPSUM BOARD WITH assembly can also act as an interior vapor diffusion retarder, Ii PERMEABLE LATEX PAINT depending on the permeance of the facing material.An inte. rior vapor diffusion retarder would significantly reduce the potential for condensation on the cavity side of the exterior CAULKING OR SEALANT insulating sheathing during the heating season and therefore ON SOLE PLATE reduce the amount of thermal resistance of the insulating (EXTERIOR OR INTERIOR) sheathing needed for limiting wetting potentials. However, this same interior vapor diffusion retarder would also signif- DRYING TO icntly reduce drying to the interior should it be required. INTERIOR aIn cases where impermeable surface treatments are uti- lized, such as wall coverings and impermeable paints, or FIG.7—MiNed climate wall construction—vinylialuminum siding where interior vapor diffusion retarders are installed(faced with impermeable sheathing. cavity insulations or sheet polyethylene), dry framing mate- III 05/01/00 MON 12:05 FAX 360 956 22217 WSU Energy Olympia 2014 CHAPTER /7—MOISTURE CONTROL FOR NEW RESIDENTIAL BUILDINGS 335 i in this rlals(wood at a moisture content of 19%by weight or lower) installed in a"tight"manner(lapped or taped joints)may be efficient and dry-applied insulations arc recommended, or, alterna• utilized to facilitate pressure equalization.Appropriate instal- nsation lively, wall assemblies must be allowed to dry prior to lation offlashings overwindow and door openings are critical ial con- enclosure. in rain screen assemblies, ideally "tucking" in behind exm- oes not Where wall assemblies with permeable interior surface nor sheathings or building papers.Where wood-based siding e water treatments have been performing satisfactorily in service and is used, tight shcathing and/or building paper provides the !rind of are subsequently covered with impermeable interior.surfacc rain control. ined by treatments(repainting with impermeable paints orwall cov- he iata- erings by new °r subsequent owners or tenants), mold and Ri Absorption/Capillary lensing mildew problems may appear at the gypsum board/surfa an ce Stollen mbly is treatment interface if the previously mentioned moisture Rainabsorption bythe vinyl or aluminum siding and siding ulation control strategies have not been effectively utilized. capillarity effects are not a concern in this wall assembly as spared a result of the inherent material properties of the vinyl and nterior aluminum- A building paper, installed only to protect the this ch- COOLING CLIMATE WALL CONSTRUCTION, impermeable rigid insulation from water absorption, is not athings WOOD-BASED SIDING, IMPERMEABLE required in this assembly for the same reason. f cavity SHEATHING(FIG. B) Rain absorption by wood-based siding and siding capillar- por diF- it, effects are a potential concern if wood-based siding is used. oisture Rain Wood-based siding should be back primed with bottom edges %rcla- Rain penetration in this wall assembly is controlled by the carefully painted.Opening of the siding laps[%in.(0.95 cm)] application of the rain screen principle where vinyl or alu- with spacers, wedges, clips, etc. should also be considered minuet siding is used and the barrier approach where wood- L131. based Sidi ng is used,The rain screen principle requires a pres- nbly sure-equalized cavity behind the cladding to perform satisfac- th torily.This is accomplished in this exampleby installingvinyl Atr Movement on the oraluminum siding overa"tight"sheathing.Cavities are cre- Airborne moisture from the exterior(infiltration ofwarm sembly ated behind the vinyl oraluminumsidingasa result ofthesid• humid air during the coolingseason)iscontrolledbyprovid- trough ing cross sections themselves(cross sections which are filled ing an air seal(air retarder)at either the interior or exterior ed cav- with insulation material or su 1,itcan pporL material are not recom- of the wall.Inthis example.this is Facilitated by sealing either I'vapor mended).ForpressureequalizarioninLhesccavitiestooccur, the exterior impermeable rigid insulation to the wall framing the extcriorsheathing munbe significantly"tighter"than the orby sealing the interior gypsum wall board to the wall fram- ingthe cladding.This is accomplished by installing the impermeable ing. This air sealing can be accomplished with adhesive, limatc rigid insulalinn(the exterior sheathing in this example)in an caulk,or some other sealant.An exterior air seal at the exec airtight manner(vertically,with all joints falling on framing rior rigid insulation in this example also facilitates pressure elative members, with the option of utilizing a sealant or adhesive equalization of vinyl or aluminum siding itself. further at sheathing joints/edges). Ahernativcly, a building paper pordif. of the Vapor Diffusion CAULKING DR SEALANT Vapor diffusion from the exterior is controlled by stalled (E TOP PLATE a vapor diffusion retarder on the exterior of the wall. this �.limate (EXTERIOR OR INTERIOR) P ' y fnsu- example, an impermeable rigid insulation is installed as is not WOOD-BASED,VINYL OR the exterior wall sheathing and acts as the vapor diffusion an be ALUMINUM SIDING retarder, of the IMPERMEABLE RIGID INSULATION stalled Comments is well Wall drying towards the interior in this wall assembly is tardcr, CAVITY INSULATION facilitated by installing a vapor-permeable paint finish on the n intc- interior gypsum wall board. Should the wall assembly BOARD WITH ce the GYPSUM become wee during service or be built initially we[ through tterlor PERMEABLE LATEX PAINT the use of wet Framing materials or the use ofwet-appliedcav- .refore CAULKING OR SEALANT ity insulations(wet spray cellulose or blown fiberglass).it can Listing ON SOLE PLATE dry to the interior due to an inward temperature and vapor (EXTERIOR OR INTERIOR) -ever, pressure gradient present as a result of air conditioning the signif• A enclosure and ambient climatic conditions. red. DRYING TO ` The facing material on fated cavity insulations installed rr uti. INTERIOR �V/ with the facing towards the interior of the wall in this climate its, or can serve to retard drying to the interior. Faced cavity (faced FIG. B—Cooling climate wall construction—rood-based siding insulations can be installed where drying to the interior is mate. with impermeable sheathing, not required, or, alternatively, the cavity insulation can be