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Architects specify wood in their building designs for many reasons, including: cost, availability, ease of construction, thermal performance, aesthetics and design versatility. Research and new product development have only added to the versatility of building with wood. This presentation reviews how to use wood to its full potential. It discusses wood’s advantages in durability and longevity, while explaining issues of quality control for wood construction and the architect’s role in promoting such control. Finally, this explains how to maintain wood buildings and maximize performance.
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Wood in Buildings:
Steps to Durability and Longevity
How to Use Wood to Its Full Potential
reThink Wood sponsors this learning unit provided by Hanley Wood, a registered
provider with the American Institute of Architects (AIA) Continuing Education Systems
(CES).
Credits earned on completion of this program will be reported to CES Records for AIA
members. Certificates of Completion are available for recordkeeping and self-reporting
purposes.
This program is registered with the AIA; as such, it is not an approval or endorsement by
the AIA of any material, product, or manner of construction.
Questions related to specific materials and services should be directed to reThink Wood
after you complete this learning unit.
AIA Best Practices
AIA Provider Number: K029
AIA Course number: BNSL1212
AIA Credit: 1 HSW/SD hour
Copyright Materials
This presentation is protected by U.S. and international copyright
laws. Reproduction, distribution, display and use of the presentation
without written permission of reThink Wood is prohibited.
© 2012, reThink Wood, www.rethinkwood.com
Specifying a building material considers structure, functionality and the
aesthetics of the built project and environment. Architects specify wood for
many reasons, including cost, availability, ease of construction, thermal
performance, aesthetics and design versatility. Research and new product
development have only added to the versatility of building with wood. New
products enable increased dimensional stability, higher strength-to-weight
ratios, and greater long-span capabilities.
Keeping wood free from decay and pests is a function of following good
design, construction and maintenance practices—all areas in which
architects can influence the optimum use of wood to create buildings that
benefit owners, occupants and the environment. Wood products generally
have the lowest environmental impacts of the major construction materials
used in the United States.
Course Description
Discuss wood’s advantages in durability and longevity.
Describe strategies for moisture control.
Explain how to maintain wood buildings and maximize
performance.
Explain issues of quality control for wood construction
and the architect’s role in promoting such control.
Learning Objectives
Section 1
DURABILITY AND LONGEVITY OF WOOD
Learning Objectives
Demand Durability
Photo: Stephanie Tracey
6-story mid-rise in the Pacific Northwest
To meet expectations for building
durability, an architect should
consider quality control such as
detailing and maintenance
techniques, as well as how the
material is handled and installed.
Why Specify Wood?
Reasons to Specify: Cost
Availability
Ease of construction
Thermal performance
Aesthetics
Design versatility
Can be used in: Single- and multi-story residential
Schools
Offices
Industrial facilities
Recreational centers
Arenas
Americana at Brand, Glendale, CA. Architect and photo credit: Togawa Smith Martin, Inc.
El Dorado High School, El Dorado, AR. Architect: CADM Architecture, Inc. Photo credit: WI Bell, courtesy WoodWorks.
Design Flexibility
Light weight
Workability
Adaptable in field
Well suited to additions and
retrofits
Can be dismantled and
materials used elsewhere
Maximum Performance
The performance of all building materials relies
on proper detail to prevent bulk water intrusion
and moisture entrapment.
Tamarack Ski Lodge Heavenly Lake Tahoe Ski Resort, South Lake Tahoe, CA. Architect: Collaborative Design Studio. Photo credit: Carrie Compton.
New Product
Development
Richmond Oval roof structure
Architect: Cannon Design.
Engineer: Fast+Epp Structural Engineers.
Photo credit: www.naturallywood.com
New Products: Structural Composite Lumber (SCL)
Glued Laminated Timber (glulam)
Pre-fabricated paneling
Cross-laminated Timber (CLT)
Benefits: Increased dimensional stability
Higher strength-to-weight
ratios
Greater long-span capabilities
Taller wood buildings
New Product
Development
Stadhaus, London. Architect and photo credit: Waugh Thistleton Sent email
Limnologen, Sweden. Architect: Ola Malm Photo credit: Midroc
Forte Building, Melbourne. Designer and photo credit: Lend Lease Send email through Lend Lease site.
Stadthaus, London
Architect: Waugh Thistleton
CLT Limnologen, Sweden
Architect: Ola Malm
Forte Building, Melbourne
Developer: Lend Lease
Exceeding Expectations
Architects can achieve superior
results when they go beyond merely
specifying wood to advocating for
the right design detailing,
construction, and maintenance
techniques that enable wood
structures to deliver decades, even
centuries, of reliable service.
Marselle Condominium, Seattle, WA. PB Architects. Photo credit: Matt Todd.
Branson Convention Center, Branson, MO. Architect: tvsdesign Atlanta, GA. Photo by Brian Gassel/tvsdesign.
Longevity
Wood
63% of wood buildings 50+ years old
Majority of wood buildings were 75+ years old
Concrete
Half of concrete buildings were 26-50 years old
1/3 of concrete buildings lasted 50+ years
Steel
80% of steel buildings were <50 years old
½ of steel buildings were less than <25 years old
Study of buildings demolished between 2000 and 2003 in Minneapolis/St. Paul
found no significant relationship between the structural system and building life.
Wood buildings had the longest life span.
Service Life
Potential threats to a long service life, such as
moisture and insects, can be controlled with pressure-
treated or naturally durable wood species.
Western red cedar's unique properties make it ideal for weather-resistant applications. Photo credit: KK Law
Pressure Treated Wood
EPA approved preservatives
AWPA standards
WWPI CheckMark program identifies code
compliant products and Best Management
Practices for treated wood in sensitive
environments
“The longer the wood lasts the lower the costs of repair or replacement.”
Dallin Brooks, WWPI
Section 2
MOISTURE CONTROL
Branson Convention Center, Branson, MO. Architect: tvsdesign Atlanta, GA. Photo credit: Brian Gassel.
Natural Moisture Levels
Wood and water are typically
compatible
Wood can absorb and
release moisture
If buildings are properly
constructed, wood performs
well in all types of climates
90% of North American
homes are built with wood
“All materials have challenges when it comes to moisture; however,
when moisture is managed properly, wood exceeds expectations.”
Cheryl Ciecko ALA, AIA, LEED AP
Wood shrinks or swells as its moisture content changes, but only when water is taken up or given off from the cell walls. Photo credit: Canadian Wood Council and Canada Wood
Moisture content (MC) measures
how much water is in a piece of
wood relative to the wood itself.
MC <19% = Dry Wood
MC > 28% = Fiber Saturation
Fiber saturation is the point at which
cell walls are holding as much water
as they can.
Additional water will go to the cell
cavity where decay and fungi can
utilize it.
Moisture Content
North America rain exposure zones. Courtesy, American Wood Council
The fiber saturation point is also the limit for
wood shrinkage
Wood only shrinks and swells when it changes
moisture content below 28%
Expansion and shrinkage occurs in the
dimension perpendicular to the growth rings:
‒ Plates
‒ Band joists
Wood Shrinkage
Photo credit: KK Law
Longitudinal shrinkage is less significant, i.e. wall studs
Natural movement of wood is not problematic with proper
design and construction but can become critical for wood
buildings 6 stories and higher
Every 4% change in MC = 1% change in horizontal
members
Engineered wood is drier and has lower shrinkage
coefficients than lumber, but are more susceptible to water
absorption
Shrinkage
MC of wood will stabilize in an environment
with consistent temperature and relative
humidity:
‒ Interior wood at 8-14% MC
‒ Exterior wood at 12-18% MC
This allows wood to perform its inherent
humidity control function, releasing moisture
in dry conditions and absorbing moisture
when the surrounding air becomes humid
Humidity Control
Start with dry wood and prevent
moisture intrusion during
construction and in building
service
Shrinkage will have occurred prior
to purchase – MC drops from 28%
to 19%
Look for S-DRY or KD stamp
Dry Lumber
Moisture loads must be accounted for and balanced in
building envelope design
Function of: ‒ Climate
‒ Surroundings
‒ Type of building
Managing Moisture Controls: ‒ Swelling
‒ Shrinkage
‒ Pests
‒ Decay
Moisture Loading
Photo credit: Stephanie Tracey
Exterior sources of moisture: Rain
Wind-driven rain
Snow
Irrigation systems
Water vapor from outdoor air
Sources of Water
Studies have found that a 4-member family can
generate 10 gallons of water vapor per day.
Interior sources of moisture: Building occupants
Poor building envelope detailing
Air leaks
Plumbing failures
Poor ventilation
Poor thermal design
Primary objective of addressing moisture loads: ‒ Keep water from entering building envelope
‒ Balance relative humidity of indoor air with building
Moisture control achieved by following the 4 Ds: ‒ Deflection
‒ Drainage
‒ Drying
‒ Durability
4 Ds of Moisture Control
Deflection
Rain deflection prevents rainwater from penetrating a wall and
roof skin and entering the building envelope
Use these design features:
‒ Pitched roofs
‒ Overhangs
‒ Flashing
‒ Rainscreen
Drainage
Drainage allows water that penetrates
the cladding, roof shingles or other
surfaces to flow along a water-resistant
plane to exit building envelope.
Rainscreen. www.buildinggreen.com 12/13/12
Drying
In properly designed building
envelope assemblies, water will
evaporate and the resulting
vapor will go through the
assembly’s outer layers,
providing vapor permeability has
been designed into the building
envelope assemblies.
Mechanism by which building envelope assemblies remove accumulated
moisture by venting and vapor diffusion.
Photo credit: KK Law
Exterior wall assemblies
must be designed to allow
sufficient drying to either the
exterior or the interior, and
the permeability of cladding,
moisture barrier, vapor
barrier and interior finish
materials will greatly affect
the wall’s overall drying
potential.
Drying
Durability
“Wood is not only our most valuable
renewable resource, it is also prized as
a versatile structural material. Its use
in construction affects the environment
in ways that are not always obvious,
such as reducing the effects of climate
change by storing carbon.”
Carol Clausen, US Forest Service
Forest Products Laboratory
Richmond Olympic Oval, Vancouver, BC. Architect: Cannon Design Photo credit: KK Law
Understanding the conditions
under which wood used in
buildings breaks down is a first
step in interrupting the process of
decay and preventing wood
deterioration.
Fungi Control
Overhangs protect end-grain of beams from moisture. Photo credit: Canadian Wood Council and Canada Wood
Decay fungi deteriorates wood
Staining fungi gives wood a blue stain deep into interior of tree
Mold & Staining fungi feed off wood’s free water and sugars but
don’t impair strength
Mold spores: ‒ Thrive in moisture & humid air
‒ Contribute to poor air quality
‒ Signal deficiency in a building’s moisture management program
MC <19% eliminates chance of mold growth
MC > 30% increases risk of mold
Most fungi grow fastest in 60-800 F range
Fungi Control
Section 3
MAXIMIZING PERFORMANCE
Campus Services Building, Western Washington University, Bellingham. Zervas Group Architects. Photo credit: Nic Lehoux
Materials Handling
During Construction
Materials handling during construction results in long-term
performance of wood and the building envelope.
“While an architect’s role typically does not extend beyond
mere specification of wood to materials handling and
construction practices, it would be ideal if architects did
provide recommendations on how wood should be treated
during construction.”
Paul Morris, Research Leader - Durability
and Building Enclosure, FPInnovations
During Construction:
Time delivery of wood close to
installation date
Provide clean, well-drained material
storage area
Inspect wood wrappers – replace with
heavy tarp if faulty
Store 6-8” off ground away from
ponding water
Place tarp or gravel pad on ground if
soil is wet
Storage area free of vegetation
Weather Protection
Weather Protection
If lumber has been significantly wetted during construction,
schedules should allow for drying of framing and sheathing
materials to19% or below.
After Installation:
Protect structure from rain and other sources of bulk water
Install roof covering and moisture barriers
Ventilate materials in building envelope before installing insulation
Avoid premature application of interior membranes (gypsum)
Allow wood framing to acclimate and lower its moisture content
Insects can cause significant property
damage to wood, fixtures and fittings,
furniture, cardboard boxes and books:
‒ Termites
‒ Carpenter ants
‒ Powder post beetles
Subterranean termites cause most damage
Total eradication is unfeasible so must
contain existing insect populations and limit
risk to buildings
Combat termites with 6-S Strategy
Termite Control
S-6 Suppression
Reducing termite populations in a particular area and
preventing spread to new areas.
Methods:
Locating and destroying
termite colonies
Burning infested wood
Heat treating reclaimed
lumber
S-6 Site Management
Careful site preparation and cleanup reduces
potential for termite infestation.
Methods:
Remove tree stumps and
buried wood from site
Remove construction debris
that contains cellulose
Drain water away from
building
Remove wooden concrete
formwork
S-6 Soil Barriers
There should be no contact between the building
woodwork and the soil or fill material.
Methods:
Exterior woodwork 6” above ground
Pressure treat any wood in contact with soil
Establish a chemical barrier between the soil and wood
S-6 Soil Barriers
Because of environmental concerns, chemical barriers in
many instances have been replaced by physical barriers.
Physical Barriers:
Precisely sized sand or crushed material beneath slab foundations
Termite mesh wraps foundation
Termiticide-impregnated membranes
Termiticidal bait systems
Slab & Foundation Details
Slabs and foundation walls should be designed to inhibit the entry of termite
and facilitate inspection of shelter tubes.
Methods:
Cap CMUs or double walls with concrete
or masonry
Keep exterior slab edges and foundation
walls free of cladding for height of
150mm from finished soil level
Terminate exterior insulation and
drainage batts 150mm below cladding
Cladding height should allow for
landscaping
Raise untreated wood from ground Height above ground of non-treated wood elements. 1Based on the U.S. model building codes and American Forest & Paper Association recommendations.
For many decades, preservative treated
framing has been successfully used to deter
termites
Wood products are also treated with borate, a
water soluble chemical that is benign to
humans, but kills insects that feed on it
Structural Protection
.
While suitable for framing and sheathing, borate
treated wood should not be used for outdoor
applications such as decks and porches since
the chemicals are water-soluble
A good quality coating, such as a three-coat film-
forming finish, prevents the borate from moving
out of the wood
Consult the American Wood Protection
Association (AWPA) standards for borate and
other preservative treatments under specific
conditions and types of termites
Structural Protection
Pressurized
‒ Combination of pressure and vacuum achieve a deep,
thorough chemical penetration
‒ Odorless water-borne option is paintable and stainable
Non-pressurized
‒ Brush, spray or dip wood in preservative
‒ Most building codes only allow field treatment for
open side of a pressure treated member that
has been cut
Termite resistant species:
‒ Heartwood of redwood
‒ Resinous heartwood of southern pine
‒ Heartwood of yellow cedar
‒ Cypress
‒ Western red cedar
Preservative Treatments
Surveillance
and
Remediation
The type of action taken against termite colonies will vary widely
depending upon the type of termite, the location and the condition
of the building.
Regular inspections are necessary:
‒ Baiting
‒ Chemical fumigation or heat
treatment
Both types of remediation must be done
by licensed contractors
Do not protect against re-infestation
Vigilant monitoring is key to identify food
sources and moisture
Protecting the structure by building with borate-treated wood products is a suppression option in certain situations. Photo credit: Louisianna-Pacific® SmartGUARD™
Wood does not decay merely because it gets wet,
but because fungi and insects consume the wood
fiber as food
Critical to separate untreated wood from the ground
and other moisture sources
Section 2304.11 International Building Code (IBC):
‒ Requires separation from soil level
‒ Addresses decay and termites
‒ Requirements for non-residential construction
applications
‒ Requirements for wood used above ground for
framing, decks, stairs, etc
Code Requirements
Section 4
QUALITY CONTROL
Ballard Library and Neighborhood Center, Seattle, WA. Architect: Bohlin Cywinski Jackson. Photo credit: Structurlam
Buildings That Work
Every building material has its challenges, and despite the
concerns outlined above, wood remains a sound choice in
most situations.
Over the years, experience has shown that the wood buildings
that work over long service lives share several characteristics. Photo credit: Tien Sher Group of Companies
Durability By Design:
Store wood properly, design the building to keep the wood dry and
observe proper maintenance practices
Dry Buildings
Basements
Because they are surrounded by
soil, basement walls are subject to
penetration by tiny amounts of
water through concrete foundation
walls that can cause wood to rot
where exterior foundations don’t
have a solid moisture barrier.
3rd Party Inspection required for all construction
materials covered by building codes
Chapter 17 of IBC, Structural Test and Special
Inspections
‒ Specific construction practices critical to
building’s structural capability
Treated wood products should:
‒ Be consistent with AWPA standards
‒ Carry the quality mark of an accredited
inspection agency of the ALSC
Buildings with
Quality Assurance
Photo credit: Jerry Parks
Untreated, exposed exterior wood should be inspected
5 years after installation and every 2 years after
Sunken paint and surface collapse indicate wood decay
Inspect cladding annually for signs of wear and green
algae stains
Examine through-wall flashing for brown stains
Properly paint or stain exposed wood
Re-treat with termiticides at appropriate intervals
Keep heavy shrubbery away from walls
Point sprinklers away from walls
Keep roof gutters unclogged
Promptly repair plumbing leaks
Regular Maintenance
WOOD:
A Material of Choice
“Wood products generally have the lowest environmental impacts of
the major construction materials used in the United States. In addition,
wood is made from trees, a renewable resource that sequesters
carbon while growing and stores carbon while in-use, thus helping to
mitigate the impacts from climate change.”
Richard Bergman, US Forest Service’s Forest Products Laboratory
Because wood is versatile and long-lasting, it will continue to
be the material of choice for many structural applications.
Keeping wood free from decay and pests is a function of
following good design, construction and maintenance
practices—all areas in which architects can influence the
optimum use of wood to create buildings that benefit owners,
occupants and the environment.
Use these resources for more information about building with wood:
http://designbuildsource.com.au/plans-for-worlds-tallest-timber-skyscraper-revealed-in-
melbourne
http://www.cwc.ca/documents/durability/BP1_MoistureAndWoodFrameBuildings.pdf
http://www.canadawood.cn/english/downloads/pdf/moisture/moisture_english.pdf
http://www.cwc.ca/documents/durability/BP6_ManagingMoistureAndWood.pdf
http://www.cwc.ca/index.php/en/design-with-wood/durability/durability-hazards/about-moisture-
and-wood
http://www.madehow.com/Volume-3/Lumber.html#b
http://www.buildingscience.com/glossary/kilndriedlumber
http://www.canadawood.cn/english/downloads/pdf/moisture/moisture_english.pdf
http://www.fpl.fs.fed.us/documnts/techline/blue-stain.pdf
http://www.fpl.fs.fed.us/documnts/informationalkits/infokit_0011_Mold_A525.pdf
http://www.ncagr.gov/SPCAP/structural/pubs/preconstruction.htm
http://www.awpa.com/standards/organization.asp
http://www.fpl.fs.fed.us/products/publications/several_pubs.php?grouping_id=100&header_id=p
http://www.awc.org/pdf/WCD6.pdf
Resources
Wood in Buildings:
Steps to Durability and Longevity
How to Use Wood to Its Full Potential
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