Southern Pine Products - Page 16

Southern Pine has long been a preferred species when pressure treatment with preservatives is required, because of its ease of treatability. The unique cellular structure of Southern Pine permits deep, uniform penetration of preservative chemicals, rendering the wood useless as a food source for fungi, termites and micro-organisms.

Most wood species do not readily accept chemical preservatives, and must first be "incised" or perforated with a series of small slits along the grain of the wood's surface. Southern Pine is one of the few wood species that does not require incising to meet American Wood Preservers' Association (AWPA) standards.

Southern Pine lumber properly treated with CCA poses no measurable risk to humans, animals, plant or marine life.

Building Code Requirements

Pressure-treated Southern Pine is recognized by all the major model building codes and regulatory agencies for use in construction.

Generally, building codes require pressure-treated or naturally durable wood for the following applications:

• Wood joists or the bottom of structural floors without joists that are within 18" of exposed soil.
• Wood girders and beams closer than 12" to exposed soil.
• Plates, sills and sleepers on concrete or masonry which is in direct contact with soil.
• Wood in permanent structures closer than 6" to soil.
• Wood supporting moisture-permeable roofs and floors exposed to weather unless separated by an impervious moisture barrier.
• Wood framing members (including sheathing) which rest on foundation walls and are less than 8" from soil.

Building codes further state that, when used in enclosed locations, the moisture content of the wood must be 19% or less at time of permanent enclosure.

Preservative Retention Levels

AWPA has developed different levels of preservative retention in treated lumber, based on its intended use.

Retention levels refer to the amount of preservative that remains in the cell structure after the pressure process is completed. Retentions are expressed in pounds of preservative per cubic foot of wood; the higher the number, the harsher the condition to which the wood may be exposed. For CCA-treated lumber and plywood, the following retentions have been established by AWPA:

If you plan to use treated Southern Pine either above ground or in contact with the ground, check the treated quality mark or end tag on each piece of lumber. It will indicate "above round" for uses such as decking not in direct contact with the soil. It will read "ground contact" for treated Southern Pine that will touch the soil, or be buried in the ground.

For a complete listing of retentions and applicable AWPA standards, refer to the table on page 18.

Design Values

Design values published in the SPIB Standard Grading Rules for Southern Pine Lumber apply to both treated and untreated Southern Pine. Also, design value adjustment factors in the National Design Specification (see "Southern Pine Adjustment Factors", page 12) apply to both treated and untreated lumber, with the exception that the load duration factor, CD, of 2.0 for impact shall not apply to structural members pressure treated with waterborne preservatives to the heavy retentions required for "marine" exposure.

Design values for dimension lumber (see "Table1," pages 9-10) are based on normal use conditions (moisture content*19%). They are intended for use in covered structures or where the moisture content in use does not exceed 19% for an extended period of time. For applications where the moisture content will exceed 19% for an extended period, tabulated design values must be multiplied by the appropriate wet service factor, CM. (See "Table A-2," page 12).

Specify Grade & Quality Marks

Each piece of lumber should be grademarked by an agency accredited by the American Lumber Standard Committee (ALSC). An ALSC-accredited grade mark on Southern Pine dimension lumber (2" or less in thickness) indicates that the lumber has been properly seasoned prior to treatment and that it meets the structural and appearance requirements established for the grade.

In addition, all treated Southern Pine should conform to the approved standards of the American Wood Preservers' Association (AWPA). Each piece should be treated in accordance with AWPA Standards and identified with a quality mark (either ink stamp or plastic end tag) by an ALSC-accredited inspection agency.

For the lumber grade mark to be valid after treatment, the lumber must adhere to the grade requirements and the moisture content of the grade represented by the grade mark.

Typical Quality Mark for Treated Lumber