15LL06 Design Considerations for Durable Wood Structures€¦ · Design Considerations for Durable Wood Structures ... American Institute of Architects ... Fourth Edition, McGraw-Hill,

DesignConsiderations

forDurableWood

Structures

“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

BorgundStaveChurchBorgund,NorwayBuiltbetween1180- 1250

Tōdai-ji, BuddhistTempleNara,JapanBuilt752andRebuilt1709

ButlerBrothersBuildingArchitect:HarryW.Jones Built1906andRenovated1974

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,

Arena Stage, Washington, DCArchitect: Bing TomPhoto Credit: Nic Lehoux

Outline


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

NotHazards

StainingFungi Weathering

Potential Hazards

Decay

InsectsAll Organic Life Requires:

1. Oxygen2. Food Source

3. Moderate Temperature4. Moisture

Mold

Outline


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

DurabilityByDesign

Source: Moisture and Wood Framed Buildings by CWC

Deflection


Deflection


Deflection

OverhangRatio

Overhang Width

Wall Height


Deflection

BarrierWallSystem


Example: Commonlymasonry(veneer)facadesarefacesealed andmaynothaveapathfordrainagebehind.

ConcealedBarrierWallSystem


Example: Alljointsandseams insheathing sealedwithcompatible anddurabletapeandfaçadedirectlyattached.

RainscreenWallSystem


Example: Inadditiontofurringstrips,dimpledmats,crinkledhousewraportexturedmeshcanalsoprovideadrainageplainancapillarybreak.

VentedRainscreenWallSystem


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.

Durability by Design – Brick Veneer

Provide minimum 1” airspace behind brick veneer.

Durability by Design – Brick Veneer

Provide a path for drainage get out from behind the wall.

DO NOT X-cut Building Paper at Window.

Durability By Design – Detailing

DurabilityByDesign– Detailing

http://www.apawood.org/buildabetterhome-walls

1” of RAIN 2000 sq ft of ROOF

1250 gallons of WATER


Avoid Horizontal Valley’s.

Flash at roof and wall intersections.


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– AirCurrent

Source: Building Science Corporation

MoistureControl– Insulation

Steelmaybehardtoinsulate: Woodinsulationexample:

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


VaporRetarders:• ClassI- 0.1permorless• ClassII– lessthan(orequalto)1.0permandgreaterthan0.1perm

• ClassIII– lessthan(orequalto)10permandgreaterthan1.0perm

“VaporBarrier”=ClassI

Source: IECC Climate Zone Map



• 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



Applicableto• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry

NOTapplicableto:• Marine• Cold• Verycold• Subarctic/arctic



Applicableto:• Cold• Verycold

NOTApplicableto• Marine• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry• Subarctic/arctic



Applicableto:• Marine• Cold• Verycold

NOTApplicableto• Mixed-humid• Hot-humid• Mixed-dry• Hot-dry• Subarctic/arctic


Outline

• BuildingExamples• PotentialBuildingHazards• UnderstandingWood• MoistureControl• DurableMaterials

• PreservativeTreatment• NaturallyDecayResistant

• ControllingTermites• LongServiceLife

PreservativeVSPressureTreated

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

Sou

rce:

Gui

de to

Pre

ssur

e Tr

eate

d W

ood,

WW

PI

PreservativeTreated- Specification

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

Preservative Treated – Wood Products

• Solid Sawn

• Plywood

• Glulam

• Parallel Strand Lumber

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


ControllingTermites

Controlling Termites: Subterranean

2006 Map Subterranean Termite Hazard Severity

Subterranean Termites—Their Prevention and Control in Buildings, US Forest Service 2006

Controlling Termites: Formosan Territory

Source: www.termite.com

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

Approx. 1”


Foundation

Floor Joist

Wood Veneer

6”8”

Ground clearance: Wood veneer

Plate/sill


Approx 1-1/2”



Foundation

Floor Joist

Wood Veneer

2”6”

Concrete clearance: Wood veneer

Porch, walk, etc

Plate/sill




Source: American Wood Council WCD 6

Floor joist

Ground clearance: Crawl space

Girder

8”

WoodPost

Moisturebarrier


Ground clearance: Wood column

WoodPost

Impervious MoistureBarrier

1”

6”

Moisture barrier


Ground clearance: Wood column

WoodPost

6”Moisturebarrier


Controlling Termites: Details


Controlling Termites - Details


Controlling Termites - 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


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

Fulton County Stadium, Atlanta, Georgia,

1965-1997

Service Life and Durability

ThisconcludesTheAmericanInstituteofArchitectsContinuingEducationSystemsCourse

WoodProjectAssistance

Questions?

WoodWorksWebsitewww.woodworks.org

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15LL06 Design Considerations for Durable Wood Structures€¦ · Design Considerations for Durable Wood Structures ... American Institute of Architects ... Fourth Edition, McGraw-Hill,

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