15ll06 design considerations for durable wood structures€¦ · design considerations for durable...
TRANSCRIPT
“TheWoodProductsCouncil” isaRegisteredProviderwithTheAmericanInstituteofArchitectsContinuingEducationSystems(AIA/CES),Provider#G516.
Credit(s)earnedoncompletionofthiscoursewillbereportedtoAIACESforAIAmembers.CertificatesofCompletionforbothAIAmembersandnon-AIAmembersareavailableuponrequest.
ThiscourseisregisteredwithAIACES forcontinuingprofessionaleducation.Assuch,itdoesnotincludecontentthatmaybedeemedorconstruedtobeanapprovalorendorsementbytheAIAofanymaterialofconstructionoranymethodormannerofhandling,using,distributing,ordealinginanymaterialorproduct.__________________________________
Questionsrelatedtospecificmaterials,methods,andserviceswillbeaddressedattheconclusionofthispresentation.
CourseDescription
Withproperdesign,detailingandspecification,woodstructurescanprovidelongandusefulserviceliveswhilealsoofferingareducedenvironmentalfootprint.Thekeyiscarefulplanningandunderstandingofenvironmentalloadsandotherexternalfactorslikelytoimpactabuildingoveritslifetime.Thispresentationprovidesanoverviewofconsiderationsrelatedtodurablewooddesign,includingmoisturemanagementtechniques,preservativetreatmentspecification,anddetailsforcontrollingtermites.
LearningObjectives
1. Determinemethodsforcontrollingmoistureinfiltrationintotheexteriorwallassemblies.
2. Reviewgoodbuildingenvelopedetailingpracticesincludingguidanceontheuseofwater,airandvaporbarriers.
3. Discussspecificationofpreservativetreatedandnaturallydecayresistantwoodmaterial.
4. Introducetermitepreventionstrategies.
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials• ControllingTermites• ServiceLife
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials• ControllingTermites• LongServiceLife
The Cathedral of Christ The Light, Oakland, CA, USADesign Team: Skidmore Owings & Merrill, Craig W. Harman, Webcor BuildersPhoto Credit: Timothy Hursley, Cesar Rubio, and John Blaustein,
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials• ControllingTermites• LongServiceLife
PotentialHazards
MOLD• Fungi• Doesnotsignificantlyeffectstructural
propertiesofwood• Someassociatedwithoccupanthealth
concerns
MOLDeffectsallmaterials!
PotentialHazards
DECAY• Fungi• Candegradestructuralcapacity• Donotcausehealthconcern
RUSTandERROSIONarepotentialhazardstoo.
PotentialHazards
INSECTS• Woodboringbeetles• Carpenterants• Termites
• Damp-woodtermites– rarelyaproblemforbuildings
• Dry-woodtermites– onlyinextremesouthernUSandMexico
• Subterraneantermites– verycontrollablerisk§ Formosantermites–more
aggressive,existinsoutheasternUS
Knowyourriskbasedongeographyanddesignforit.
Formosan Termite
CarpenterAnts
Wood BoringBeetles
Potential Hazards
Decay
InsectsAll Organic Life Requires:
1. Oxygen2. Food Source
3. Moderate Temperature4. Moisture
Mold
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials• ControllingTermites• LongServiceLife
Understanding Wood: Hygroscopic
Free Water VS Bound Water
Fiber Saturation Point: Point at which cell walls are completely saturated, cell cavities are empty (i.e. no free water but still has all its bound water)
Understanding Wood: Hygroscopic
Picture Source: Panshin, A.J. and de Zeeuw, C., (1980) Textbook of Wood Technology, Fourth Edition, McGraw-Hill, inc.
Moisture Content • Fiber Saturation = 28% MC• Code required to be < 19%
MC at building close • Wood still has ability to
absorb water between 19-28%
Understanding Wood: Orthotropic
Wood is orthotropic, meaning it behaves differently in its three orthogonal directions: Longitudinal (L), Radial (R), and Tangential (T)This is a direct result of the arrangement of wood cells
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl
• BulkWaterIntrusion• AirflowCurrent• VaporDiffusion
• DurableMaterials• ControllingTermites• LongServiceLife
Moisture Control
WettingBulk water intrusion
Air current induced moisture vapor
movement
Vapor migration by diffusion
Drying
Evaporation or diffusion
Directionally effected by humidity, temperature
and pressurization
MoistureControl
WettingBulkwaterintrusion
Aircurrentinduced
moisturevapor
movement
Vapormigrationby
diffusion
DryingEvaporationordiffusion
Directionallyeffectedby
humidity,temperature
andpressurization
Source: Moisture and Wood Framed Buildings by CWC
Deflection
OverhangRatio
Overhang Width
Wall Height
BarrierWallSystem
Source: Moisture and Wood Framed Buildings by CWC
Example: Commonlymasonry(veneer)facadesarefacesealed andmaynothaveapathfordrainagebehind.
ConcealedBarrierWallSystem
Source: Moisture and Wood Framed Buildings by CWC
Example: Alljointsandseams insheathing sealedwithcompatible anddurabletapeandfaçadedirectlyattached.
RainscreenWallSystem
Source: Moisture and Wood Framed Buildings by CWC
Example: Inadditiontofurringstrips,dimpledmats,crinkledhousewraportexturedmeshcanalsoprovideadrainageplainancapillarybreak.
VentedRainscreenWallSystem
Source: Moisture and Wood Framed Buildings by CWC
Example: Furringstripsfastenedtoframingthroughinsulatingsheathingwithopenings attopandbottomprovidedwithscreentopreventinsect entry.
• Addressbulkwaterthatgetspastcladding• Appliedatexterior• Ex:buildingpapers/wraps(NOTall)• Limits liquidwaterpassingthrough
WeatherBarrier
• Stopsmovementofairunderpressure• Appliedatinteriororexterior• Ex:Boardstock,tapes
AirBarrier
• Slowmovement ofwatervaporbydiffusion• Installed onwarmsideofinsulation• Maynotberequiredordesired• Lowlevelofpermeability
VaporBarrier/Retarder
DurabilitybyDesign- GuidetoBarriers
WeatherBarriers
Perforated
Housewraps
Unperforated
Housewraps
BuildingFelt/
Paper
WaterResistant Lessthanunperforated
Yes Yes,variesgreatly
VaporPermeable Yes Yes Yes
AirResistant Yes Yes Onlyifpenetrationsareallsealed
MoistureAbsorptive No No Yes,variesgreatly
TearResistant Yes Yes Variesgreatly
UVResistant Variesgreatly Variesgreatly No
MoistureTolerant Yes Yes No
DurabilityByDesign– ReservoirCladding
Reservoircladdingsystemsneedanairspacetodryandeliminatecapillaryaction.
DurabilitybyDesign- Stucco
Moistureloadatwindowheader,sillsandcorners
Needtominimizeabilitytostorewater
Durability by Design - Stucco
Ensure clean sand is used in Stucco mix.
Specify building wrap with built in drainage or
two layers of building wrap.
1” of RAIN 2000 sq ft of ROOF
1250 gallons of WATER
Durability By Design – Detailing
Avoid Horizontal Valley’s.
MoistureControl
WettingBulkwaterintrusion
Aircurrentinducedmoisturevapormovement
Vapormigrationbydiffusion
DryingEvaporationordiffusion
Directionallyeffectedbyhumidity,temperatureandpressurization
Change in relative humidity (rh) of air at 70F cooled to 35F (with no moisture added or removed)
Moisture Control - Condensation
INSIDE OUTSIDE
70DegreesF30%RelativeHumidity
DewPointLocation
DewPoint
0DegreesF
MoistureControl- Condensation
MoistureControl– AirSealing
ExteriorAirBarrier
InteriorAirBarrier
Ease ofinstallation
Nointersectingwallsandfewerpenetrations
Moreintersectingwallsandpenetrations todetailaround
AddressesWind-washing
Preventswind-washing ofthecavityinsulation
Usingsemi-rigidinsulation canpreventtheneedto addresswind-washing
Controllingmoistureloads
Control entryofexteriorhothumidairintoinsulatedcavities inhothumidclimates.
Controlentryofinteriormoistureladenairintoinsulated cavityduring heating
Moisture Control
WettingBulk water intrusion
Air current induced moisture vapor
movement
Vapor migration by diffusion
Drying
Evaporation or diffusion
Directionally effected by humidity, temperature
and pressurization
MoistureControl- VaporDiffusion
VaporDiffusion• Moisturetransferthrough
amaterialmovingfromwettertodryer
• VaporPressureistheweightofthewaterintheair.
• Higherhumidityairweighsmorecreatingapressurethatmovewaterfromwettertodryer
MoistureControl– VaporRetarders
Source: Building Science Corporation
VaporRetarders:• ClassI- 0.1permorless• ClassII– lessthan(orequalto)1.0permandgreaterthan0.1perm
• ClassIII– lessthan(orequalto)10permandgreaterthan1.0perm
“VaporBarrier”=ClassI
MoistureControl– VaporRetarders
• DonotrequireanyclassofVaporretarderontheinteriorsurfaceofinsulation ininsulatedwallandfloorassemblies
Zone1-3
• DonotrequireanyclassofVaporretarderontheinteriorsurfaceofinsulation ininsulatedwallandfloorassemblies
Zone4(exceptMarine)
• Class IIorIII(orlower)mayberequireddepending onpermeance ofsheathingandcladding.Higherclasscanbeappliedifdewpoint iscontrolled(requiresmodeling).
Zone4(marine),5-7
MoistureControl– ClimateZones
Source: Build America US Department of Energy (http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/4_3a_ba_innov_buildingscienceclimatemaps_011713.pdf)
MoistureControl– GoodExample
Applicableto• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry• Marine• Somecolderregions(5/6)
NOTapplicableto:• Verycold• Subarctic/arctic
Source: Building Science Corporation
MoistureControl– GoodExample
Applicableto• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry
NOTapplicableto:• Marine• Cold• Verycold• Subarctic/arctic
Source: Building Science Corporation
MoistureControl– GoodExample
Applicableto:• Cold• Verycold
NOTApplicableto• Marine• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry• Subarctic/arctic
Source: Building Science Corporation
MoistureControl– GoodExample
Applicableto:• Marine• Cold• Verycold
NOTApplicableto• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry• Subarctic/arctic
Source: Building Science Corporation
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials
• PreservativeTreatment• NaturallyDecayResistant
• ControllingTermites• LongServiceLife
2303.1.8 Preservative-treated wood.
Lumber, timber, plywood, piles and poles supporting permanent structures required by Section 2304.11 to be preservative treated shall conform to the requirements of the applicable AWPA Standard U1 and M4 for the species, product, preservative and end use. Preservatives shall be listed in Section 4 of AWPA U1. Lumber and plywood used in wood foundation systems shall conform to Chapter 18.
However code compliant preservative treated products can also follow:
• 104.11 Alternate materials and methods
• ICC reports can also be provided for proprietary treatments and products under this provision
As defined by the IBC in Chapter 23
Preservative Treated
PreservativeTreated- Specification
ICCreportscanalsohavealotofinformationthatcanbeusefulinspecificationforbothproprietaryandnonproprietarytreatments.
• Conditionsofuse• Fastenerrecommendations• Structuralcapacity
http://www.icc-es.org/Reports/index.cfm
WaterborneCopperBased:• ACQ– AlkalineCopperQuat• ACZA(Chemonite) – AmmoniacalCopperZincArsenate
• CA– CopperAzole• CCA– ChromatedCopperArsenate• PTIandEL2 – Carbon-basedpreservatives
• MCA–MicronizedCopperAzoleBorateBased:• SBX– InorganicBoron
Oilbased• Pentachlorophenol• CopperNaphthenate
Creosote
PreservativeTreated– TreatmentTypes
PreservativeTreated- Incising
Pressure-treatedDouglas-fir
Pressure-treatedSouthernPine
Photo from University of Tennessee Forest Products Extension
PreservativeTreated–SpecExamples
1. SillplatesshallbetreatedinaccordancewithAWPAStandardU1totherequirementsofUseCategory2(UC2).
2. Sillplatesshallbetreatedwithwaterbornepreservatives inaccordancewithAWPAStandardU1totherequirementsofUseCategory2(UC2).
3. Sillplatesshallbetreatedwithwaterbornepreservatives inaccordancewithAWPAStandardU1,CommoditySpecificationA,totherequirementsofUseCategory2(UC2).
4. Sillplatesshallbesouthernpinelumber,treatedwithwaterbornepreservatives inaccordancewithAWPAStandardU1,CommoditySpecificationA,totherequirementsofUseCategory2(UC2).
5. Sillplatesshallbesouthernpinelumber,treatedwithinorganicboron(SBX)inaccordancewithAWPAStandardU1,CommoditySpecificationA,totherequirementsofUseCategory2(UC2).
ProprietaryTreatmentsspecificationguidelinesareusuallyveryclearlyprovidedbythetreatedproductsupplierontheirwebsite.
PreservativeTreated- Fasteners
IBC2304.9.5.1• Hot-dippedgalvanizedsteel
§ abovegrade• Stainlesssteel
§ belowgrade,§ salt-waterexposure,§ severeconditions
• Siliconbronze§ Specialuse
• Copper§ Specialuse
PreservativeTreated– LCAComparison
Source: Conclusions and Summary Report on an Environmental Life Cycle Assessment of Borate –Treated Lumber Structural Framing with Comparisons to Galvanized Steel Framing, Treated Wood Council 2012
CopperNapthenateAtleast2%coppersolution
Availablefieldtreatmentproducts
• Copper-Green• Copper-GreenBrown• WoodlifeCopperCoat• CopperCareCu-NapConcentrate
• ArmorAllEndCutWoodPreservative
Preservative Treated – Field Treatment
Naturally Decay Resistant Species
Source: US Forest Products Lab Wood Handbook Chapter 14 Biodeterioration, Clausen 2010
Cell Structure: Heartwood & Sapwood
Sapwood: Outer, lighter colored band which conducts moisture and sap, stores biochemicals and carbon, and is the metabolically active zone (living sapwood cells are agents of heartwood formation)
Cell Structure: Heartwood & Sapwood
Heartwood: darker colored core, long term storage of extractives which are biochemicals that provide natural durability to wood. They are formed at the heartwood-sapwood interface and infiltrate cells
throughout the heartwood region
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials• ControllingTermites• LongServiceLife
Controlling Termites: Subterranean
2006 Map Subterranean Termite Hazard Severity
Subterranean Termites—Their Prevention and Control in Buildings, US Forest Service 2006
DurabilityDetailing
The6SApproachtoSubterraneanTermiteControl
Suppression SiteManagement
SoilandPhysicalBarriers
SlabandFoundationDetails
StructuralProtection
Surveillanceand
Remediation
ControllingTermites:SiteManagement
Removefromsite• treestumps• allwood/cellulosecontainingdebris• Formwork(don’tleaveembeddedinfoundation)
SoilWork• Donotuseexcavationspoilunderwoodframeelements• Drainwaterawayfrombuilding(slope5%for10’)• Keepnon-treatedwoodawayfromsoil(6”-8”codeminimums)
PhysicalBarriers• 4”thicksandorcrushedstone(1/16-1/10”Dia)beneathslaband/oralonginsideandoutsideoffoundationwall
• Installsheetmetalbetweentopoffoundationandsillplate• Wrapperimeterfoundationinmeshtoprotectat/belowgradepenetrations(1/32”gridspacing)
• Marinegradestainlesssteelmeshhas20yrservicelife• Openingsinslab/stemwallsealedwithnon-shrinkgrout
SlabsandFoundations• Slabscontroljointsandcracksdonnotexceed1/25”• Stemwallsexposedfor8”abovegradetoallowinspection• Keepcrawlspaceaccessinfloorinsteadoffoundationwalls
ControllingTermites:Barrier/Foundations
ControllingTermites:Details
Foundation
FloorJoist
Brick Veneer
8”
Ground clearance: Brick Veneer
Plate/sill
Foundation
Floor Joist
Wood Veneer
6”8”
Ground clearance: Wood veneer
Plate/sill
ControllingTermites:Details
Foundation
Floor Joist
Wood Veneer
2”6”
Concrete clearance: Wood veneer
Porch, walk, etc
Plate/sill
ControllingTermites:Details
Floor joist
Ground clearance: Crawl space
Girder
8”
WoodPost
Moisturebarrier
ControllingTermites:Details
Ground clearance: Wood column
WoodPost
Impervious MoistureBarrier
1”
6”
Moisture barrier
ControllingTermites:Details
Controlling Termites – Structural
Preservative Treated Wood• CCA for interior damp, exterior above ground and
exterior ground contact applications• Borate treatments for interior dry and interior damp
applications
Termite Resistant species• Yellow Cedar• Cypress• Redwood• Western/Eastern Red Cedar
Outline
• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials• ControllingTermites• LongServiceLife
12
47
18 19
7
0-25 26-50 51-75 76-100 100+
ServiceLifeandDurabilityN
umbe
r of B
uild
ings
Age Class – YearsSource: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada 2004
ServiceLifeandDurability
0%
20%
40%
60%
0-25 26-50 51-75 76-100 100+
Concrete
Steel
Wood
Per
cent
of B
uild
ings
Age Class – YearsSource: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada
Source: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada 2004
ServiceLifeandDurabilityP
erce
nt o
f Bui
ldin
gs
Age Class – YearsSource: Demolition Study – Forintek Canada Corporation, Vancouver, B.C., Canada 2004
Demolition study (service life of buildings)• Findings suggest no significant relationship between the structural
system and the actual useful life of the building.
Reasons for demolition:1. Changing land value2. Building does not meet current needs3. Lack of maintenance of non-structural components
Lessons:• Determine realistic service life
§ Resources: ISO 15686, CSA 478-95• Find balance between building’s intended use and adaptability
§ Buildings designed for all purposes don’t lend themselves to efficient/sustainable design
http://www.woodworks.org/wp-content/uploads/2012/02/fpi-survey-actual-service-lives.pdf
Service Life and Durability
ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse
WoodProjectAssistance
Questions?
WoodWorksWebsitewww.woodworks.org