Specifying Treated Wood - BCBEC
Transcript of Specifying Treated Wood - BCBEC
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Specifying Treated Wood
Paul I Morris, Group Leader –
Durability and Protection
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Presentation Outline
Treated wood in the 2010 NBCC and other uses
Overview of CSA O80 Series: Wood Preservation
Understanding Use Categories 1 through 5A
Products and Use Categories for specific exposures
Treatment requirements for plywood and lumber
Selecting species for strength, stability and treatability
Selecting the appropriate preservative
Pre- and post-treatment conditioning
Third party quality assurance
Appropriate and inappropriate product substitution
Handling of treated wood to maximize durability
Long term performance
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Treated Wood in the 2010 NBCC
Where wood is required to be treated to resist
termites or decay, such treatment shall be in
accordance with CSA O80.1-08, “Specification
of Treated Wood” Table 2, “Use Categories for
Specific Products, Uses and Exposures”
Wood that is required to be treated to resist
termites or decay shall be identified by a mark
to indicate the type of preservative being used
and conformance to the relevant required use
category
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Treated Wood in the 2010 NBCC
In localities where termites are known to occur,
clearance between structural wood elements
and the finished ground level directly below
them shall be not less than 450 mm and, except
as provided in Sentence (2), all sides of the
supporting elements shall be visible to permit
inspection, or
structural wood elements, supported by
elements in contact with the ground or exposed
over bare soil, shall be pressure-treated with a
chemical that is toxic to termites.
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Treated Wood in the 2010 NBCC
Termite Infestation in Canada
Southeast coast
Vancouver Island,
Sunshine Coast,
Okanagan
Winnipeg
Southern Ontario
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Treated Wood in the 2010 NBCC
Structural wood elements shall be pressure-
treated with a preservative to resist decay,
where the vertical clearance between
structural wood elements and the finished
ground level is less than 150 mm* (see also
Articles 9.23.2.2. and 9.23.2.3.), or
*Ground level always rises
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Treated Wood in the 2010 NBCC
Structural wood elements shall be pressure-
treated with a preservative to resist decay,
where:
the wood elements are not protected from
exposure to precipitation,
the configuration is conducive to moisture
accumulation, and
the moisture index is greater than 1.00.
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Treated Wood in the 2010 NBCC
Canadian Locations with Moisture Index >1
Moisture Index: <0.7 0.7-0.85 0.85-1
>1 Western BC, Gulf of St. Lawrence, Maritimes
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Treated Wood in the 2010 NBCC
Structural wood elements used in retaining
walls and cribbing shall be pressure-treated
with a preservative to resist decay, where
the retaining wall or cribbing supports ground
that is critical to the stability of building
foundations or
the retaining wall or cribbing is greater than
1.2 m in height.*
* Excludes most raised beds
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Treated Wood in the 2010 NBCC
Where wood is protected in accordance with
UC1 or UC2 using an inorganic boron*
preservative the wood shall be
protected from direct exposure to water during
and after the completion of construction, and
separated from permeable supporting
materials by a moisture barrier that is resistant
to all expected mechanisms of deterioration in
the service environment if the vertical
clearance to the ground is less than 150 mm.
* Extended exposure to rain causes leaching
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Other Uses for Treated Wood
Any wood structure exposed to rain where
design life is more than a few years and
– Safety is important
– Appearance is important
Any wood component in a building
that may get wet and stay wet and
– Is not easy to inspect
– Is difficult to replace
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Climate Change Increasing Decay Hazard
*Scheffer 1971
Setliff 1986
Scheffer Index
(T°, Rain)
1940s – 1970s*
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Climate Change Increasing Decay Hazard
Scheffer Index
(T°, Rain)
1970s – 1990s*
*Morris & Wang 2008
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Overview of CSA O80 Series
Originally for industrial products
– Poles, ties, bridge timbers, docks
Rise of residential treated wood market required
new standards
– Decks, fences, gazebos
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Overview of CSA O80 Series-08
Based on a Use Category System
Matches level of treatment to decay/termite risk
– Formalizes some earlier categories. Adds others
Derived from USA AWPA standards
Compatible with ISO 21887
– Committee secretariat and chair were Canadian
Designed to be more accessible to specifiers
– Start at Table 1 to understand use categories
– Go to Table 2 to locate products and uses
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Understanding Use Categories
CSA O80.1 Table 1*
Use categories and associated service conditions
Use
Category
Service
Conditions
Use
Environment
Typical
Products
UC1 Interior, above
ground, dry
Protected from
weather
Interior
framing
UC2 Interior, above
ground, damp
Protected but
can be exposed
to moisture
Sillplates
* Available at www.durable-wood.com
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Understanding Use Categories
CSA O80.1 Table 1
Use categories and associated service conditions
Use
Category
Service
Conditions
Use
Environment
Typical
Products
UC3.1 Exterior above
ground, coated
Protected by
coating. Free
draining
Coated
millwork,
siding, trim
UC3.2 Exterior above
ground
uncoated
Exposed to all
weather cycles
Deck boards,
joists, railing,
fence boards
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Understanding Use Categories
CSA O80.1 Table 1
Use categories and associated service conditions
Use
Category
Service
Conditions
Use
Environment
Typical
Products
UC4.1 Exterior
ground contact
Exposed to all
weather cycles
Fence and
deck posts
UC4.2 Exterior
ground contact
Critical uses
Exposed to all
weather. High
decay potential
PWF, Utility
Poles
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Understanding Use Categories
CSA O80.1 Table 1
Use categories and associated service conditions
Use
Category
Service
Conditions
Use
Environment
Typical
Products
UC5A Coastal waters
including
brackish water
Continuous
salt water
exposure
Piles, bulk-
heads and
bracing
UC5B Not encountered in Canadian Waters
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Understanding Use Categories
UC 1
UC 2
UC 3.2
UC 4.1
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Understanding Residential Product Groups
CSA O80.1 Clause 4.3.2
Product Group A
Above Ground, UC 3.2
Thickness < 25mm
– a) Easily inspected, light duty, appearance grade.
Low decay potential. Design life not limited by decay.
– b) Construction materials behind cladding such as
battens for rainscreen or roofing.
Products: Fence boards, rainscreen battens
No contact with untreated wood, unless durable
– Prevents direct attack by mycelium of decay fungi
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Understanding Residential Product Groups
CSA O80.1 Clause 4.3.2
Product Group B
Above Ground, UC 3.2
Thickness < 40mm
– a) Turned, profiled, easily inspected, appearance
grade. Low decay potential. Life not limited by decay.
– b) Lumber < 150mm wide (excludes sillplates)
Typical Products: Spindles, deck boards.
No contact with untreated wood, unless durable
– Prevents direct attack by mycelium of decay fungi
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Understanding Residential Product Groups
CSA O80.1 Clause 4.3.2
Product Group C
Above Ground, UC 3.2
Thickness < 40mm
Width > 150mm
Easily inspected (excludes sillplates)
Typical Products: deck joists, ledger board
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Understanding Residential Product Groups
CSA O80.1 Clause 4.3.2
Product Group D
Ground Contact, UC 4.1
Thickness > 40mm < 155
Easily inspected
Typical Products: Fence and deck posts
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Understanding Residential Product Groups
Structural and ground
contact needs incising
Shallow penetration OK
for above ground, low
decay hazard, if cuts are
field-treated.
spores
Actively growing fungus
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Understanding Use Categories
UC 1 Group A
UC 2 Group C
UC 3.2 Group B
UC 4.1 Group D
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Determining the Use Category for Products
CSA O80.1 Table 2* (alphabetical)
Product End Use Exposure UC Clause
Batten -
plywood
Rainscreen cavity Above ground 3.2 9.7
Batten -
sawn
Rainscreen cavity Above ground 3.2 9.2.2.5
Bender
board
General Ground contact 4.1 9.2
* Available at www.durable-wood.com
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Requirements for Plywood and Lumber
Ten years ago it was simple
– Preservative CCA
– Penetration 10mm
– Retention
• Above ground: 4.0 kg/m3
• Ground contact: 6.4 kg/m3
New preservatives have various retentions
New standards have various penetrations
Today, don’t worry about penetration/retention
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Specify
Use Category
Residential product Group (if applicable)
– Excludes CCA
Wood Species
Preservative (ACQ and CA interchangeable)
Post treatment conditioning (if applicable)
Labeling as CSA compliant
3rd Party quality assurance (if available)
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Selecting the Appropriate Wood Species
Strength
– Douglas fir is very strong but not very treatable
Stability
– Lodgepole pine is stable but not very treatable
Treatability
– Hemlock is treatable but not very stable
– Pacific silver fir is very treatable but not as strong
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Selecting the preservative
Interior framing SBX (borate)
Residential lumber ACQ or CA
Shingles CCA
Plywood CCA
PWF CCA
Utility poles CCA
Bridge timbers Pentachlorophenol
Railroad ties Creosote
Piling Creosote
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Pre- and post-treatment conditioning
Drying
– Ideally air drying to 25% MC
– Kiln drying can be too aggressive
Incising
– Perforation improves penetration
Fixation
– Required for CCA treated wood
Re-drying
– Normally required for borate treated framing
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Quality Assurance
November 2010: none of the material in the
stores is certified as meeting CSA standards
NBCC requires marking for CSA compliance
QA available from various inspection agencies
Third party QA by
– Canadian Wood Preservers Bureau (Ontario)
– CLSAB (Abandoned)
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Product Substitution
Product Substitute OK Not OK
ACQ CA Always
ACQ or CA CCA Plywood
Shingles
Other
residential
ACQ or CA Borate Indoors Outdoors
CCA ACQ or CA Plywood
Shingles
PWF
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Care and Handling to Ensure Durability
Where possible fabricate prior to treatment
Ideally allow to air dry before installation
Place uncut ends in ground contact
Field treat all cut ends
Cap tops of posts to shed water
Apply water repellant if checking is a concern
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Long Term Performance
How long does it last?
Documented life in FPInnovations field tests
when treated to CSA O80 Standards
– CCA treated jack pine roundwood posts >>60 years
– CCA treated WRC shingles/shakes >>30 years
– CCA treated unincised hem-fir decking >>30 years
– CCA treated incised SPF lumber in soil >>25 years
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Long Term Performance
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5
Years of Exposure
AW
PA
Rating
untreated white spruce untreated western red cedar
ACQ-D 6.4 kg/m3
Linear (untreated white spruce) Linear (untreated western red cedar)
Linear (ACQ-D 6.4 kg/m3)
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Any Questions