|
 |
| Termite Resistant Structures |
PRESSURE-TREATED SOUTHERN PINE
Properly treated Southern Pine lumber components offer
long-term protection from a wide array of natural predators
which might otherwise host on unprotected wood under the
right exposure conditions. These predators include fungal
decay (rot), and a wide variety of wood-destroying insects. Termites
are by far the most damaging of these insects and the Formosan
termite species is the single
most damaging termite in the
world. The preservative treatment
process renders the wood
useless as a food source and is, in
fact, toxic to termites if they
attempt to consume it.
Treated wood products have
long been used in this country to
extend the service life of structures when used in harsh, unprotected
outdoor environments where decay and insect attack are
most likely to occur. The interior wood framing of a home —
typically protected from excessive moisture — has traditionally
not been considered to be at high risk to these predators. The
Formosan termite has changed that philosophy.
It is increasingly evident that any wood component within
the range of this predator — including enclosed, elevated dry
structural wood framing — is at risk. In fact, the damage
caused to a structure’s framework is usually far more advanced
(often to the point of failure) before detection, because this
species can thrive for as long as the wood food source exists.
Often, Formosan termites remain hidden deep within wall,
floor, and roof cavities until extensive damage is done.
It is becoming increasingly evident that the only certain
method of providing protection for the wood framework in
structures within the range of the Formosan termite is to
remove the wood as a food source. That is why the wood products
industry is recommending to builders and homeowners
alike in termite-infested areas of the country that they strongly
consider using pressure-treated wood products for the entire
framework of their homes. The most positive protection is to
consider "whole house" treatment; that is, provide treatment
protection to all wood structural framing members of the
building. This concept is already required by building codes in
Hawaii. In early 2000, this practice was seriously considered as
a mandate within Louisiana because of the severe problems
caused by the Formosan subterranean termite, particularly in
the Southern parishes where termite activity remains at epidemic
levels in both the New Orleans and Lake Charles areas.
Pressure-treated Southern Pine lumber products are the
ideal components for structural framing packages, affording
complete protection from both termites and decay in the high-moisture,
moderately warm climates of U.S. Southern states,
regions where Formosan termites thrive. Several preservative
treatment options are available for solid-sawn lumber products
and are highly effective against Formosan termites. Regardless
of what treatment option is selected, the ideal wood species
choice for treated structural framing is Southern Pine.
Southern Pine is ideally suited for structural framing
because of its high strength. It is the strongest structural lumber
for framing and engineered applications in North America.
In addition, it is the most treatable softwood species. Treated
Southern Pine dimension lumber products suitable for
repelling termites are also readily available in a wide range of
grades and sizes and at competitive prices.
TREATMENT OPTIONS
The American Wood-Preservers’ Association (AWPA) has
approved the use of several waterborne treatments effective
against Formosan termites that would be appropriate for residential
or commercial
enclosed (interior) framing
applications. These preservatives,
relatively new to the
U.S. market, include Alkaline
Copper Quat (ACQ), Copper
Azole and Borates.
Chromated Copper Arsenate
(CCA), the most widely
used wood preservative in the past, has been withdrawn for use
in interior framing applications. However, CCA-treated timbers,
piles and posts are still approved for exterior uses such as foundations.
AWPA USE CATEGORY SYSTEM
The American Wood Protection Association Use Category System (UCS) establishes major exposure conditions that wood products are subjected to in service. The UCS helps users identify the exposure condition for specific products and end-use environments, and then specify the acceptable preservatives and retention levels necessary for that application. Interior exposure conditions are designated Use Category UC1 (Interior, Dry) and UC2 (Interior, Damp).
Treated wood must meet minimum requirements for preservative penetration and retention for use in a particular service condition. Penetration refers to the depth a preservative must permeate into the wood fiber during the pressure-treating process. Retention levels refer to the amount of preservative that remains in the wood after the pressure-treating process is complete.
Structural wood products and preservative retentions typically used for interior framing in termite resistant structures are listed in the table below.
AWPA USE CATEGORY SYSTEM
Wood products pressure treated with waterborne chemicals
have very high moisture contents following removal from the
treatment cylinder. If the treated product is intended for a
structural framing application sanctioned by building codes, it
is necessary to redry or kiln dry after treatment (KDAT) the
material to assure dimensional stability of the product. After
treatment, dimension lumber (2" to 4" thick; 2" and wider)
needs to be redried to 19% moisture content (MC) or less.
Therefore, any specification for treated framing should include
moisture content requirements after treatment.
|
|
Previous
