Southern Pine Porch
Flooring
 The
porch has withstood the test of time as an icon of American
architecture, adding comfort, distinction and value.
Today's home designs incorporate the porch as a natural
extension of the family's living space.
Southern Pine flooring has enjoyed
a long history in porch construction. As with indoor
flooring material, the effect of moisture in contact
with wood is a top concern when designing and building
a porch.
Southern Pine, combined with the technology
of wood preservation, is a superior porch flooring choice.
With its built-in resistance to decay and termites, pressure-treated
Southern Pine porch flooring, properly installed, will
provide decades of satisfying service.
This section provides information related
to material specification, handling and storage, installation,
finishing, and general construction considerations for
porch floors using preservatively treated Southern Pine.
Sizes, Grades and Patterns
The size, grade and pattern of flooring
utilized in porches will depend upon the type of protection
given to the structure. Porches without complete roof
protection are generally constructed in the same manner
as outdoor decks, incorporating a surface of either 2"x6" nominal
size or 5/4x6 radius-edge pressure-treated Southern Pine.
A dimension (2x) lumber grade of No.1 provides optimum
appearance. Radius-edge decking is available in Premium
or Standard grades.
The recommendations outlined in this
section refer to flooring for fully-covered porches.
Porch flooring is similar in sizes, grades, and patterns
as the interior flooring described earlier in this booklet.
Typically, nominal thicknesses are
1" and 1-1/4" (3/4" and 1" actual) with the tongue-and-groove
pattern, available in widths of 4" to 6" nominal (3-1/8" to
5-1/8" actual). The grade of C&Better is most-often specified
for porch flooring applications. Refer to Table 1 under
grades for complete descriptions of flooring grades.
To combat the deteriorating effects
of outdoor exposure, moisture, decay and termite attack,
pressure treatment with a waterborne preservative is
recommended for all wood components of the porch. These
preservatives are odorless and paintable, offering superior
protection to Southern Pine products in severe outdoor
exposure conditions.
Standards developed by the American
Wood Preservers' Association (AWPA) govern the use and
specification of all wood preservatives used in pressure-treating
processes. Most building codes require that wood in close
proximity to the ground be pressure-treated to specific
preservative retention levels, according to AWPA Standards.
This requirement applies to flooring and floor joists
within 18" of exposed soil and structural materials such
as columns, posts, girders and beams, within 12" of exposed
soil. The preservative retention level specified for
above-ground uses of Southern Pine is 0.25 pcf (pounds
of preservative per cubic foot). For ground contact,
a preservative retention level of 0.40 pcf meets AWPA
Standards.
Generally, the 0.25 pcf retention is
adequate for porch flooring, floor joists, and other
porch materials used in above-ground applications, while
the 0.40 pcf retention is required for wood in direct
contact with the soil, such as posts and columns.
For complete details about products,
standards and applications, consult the booklet Pressure-Treated
Southern Pine, available from the Southern Pine Council.
Prior to pressure treatment, a package
of Southern Pine T&G porch flooring is at a moisture
content of 12% for the majority of pieces if specified,
represented, and grade marked as kiln-dried (KD). Refer
to important information under the section "Wood and
Water Relationships" under Product Application . With
a waterborne preservative, water is part of the pressure-treating
process, greatly increasing the moisture content of the
wood, often to a moisture content of 50% and higher.
 For
porch flooring, the specification of material that is
kiln-dried-after-treatment (KDAT) is highly recommended.
Redrying the treated material will return each piece
to a workable moisture content, generally to 19% or less.
The advantages of KDAT flooring material include enhanced
dimensional stability, plus reduced tendencies to warp,
twist, and cup.
The same basic rules for proper storage,
handling, and shipping as discussed earlier for interior
flooring also apply here; see product application . Remember,
the pressure treatment of wood does not prevent the normal
passage of moisture in and out of lumber. KDAT Southern
Pine flooring will react the same as untreated interior
flooring when exposed to moisture prior to installation
and finishing.
A period of acclimation should be given
to both the porch framing components and the pressure-treated
porch flooring. Upon completion of the porch framing,
it is common for experienced builders to allow one to
two weeks for the framing materials to reach an equilibrium
moisture content (EMC) with the exterior conditions,
prior to flooring installation. This practice will reduce
potential problems of buckling or separation of the flooring
if installed on the framing too soon.
Proper acclimation of the flooring
begins with its delivery to the job site. The material
should be unloaded in a dry place and stacked on stringers
to permit adequate air circulation. A layer of polyethylene
should be positioned directly under all packages of flooring
to prevent moisture absorption from the ground. If the
temporary storage area is not fully protected from precipitation,
the flooring must be loosely covered for protection from
moisture (4-mil polyethylene is commonly used), yet allowing
adequate circulation of air within the package. If at
all possible, do not store the flooring in an area that
receives direct sunlight most of the day, or in an enclosed,
heated space. These conditions can allow the flooring
to equalize at a moisture content too low for its intended
use.
Generally, one to two weeks is considered
an adequate acclimation period for KDAT porch flooring.
The average moisture content of wood materials used in
exterior applications is 12% for most areas of the U.S.
 Reducing
the opportunities for dimensional changes to the material
due to moisture fluctuations is the key to long-term
performance of the porch floor. Proper porch flooring
installation actually involves applying the finish prior
to installation.
Many builders begin with a coat of
a water-repellent sealer on the top of all floor joists,
providing added protection against joist expansion due
to excessive collection of moisture.
For the porch flooring, begin with
a coat of paintable water-repellent sealer to all four
sides and the ends, followed by (after adequate drying
time) a coat of high-quality, mildew-resistant oil-based
primer for exterior use. Consider applying a coat of
the final oil-based porch enamel to the tongue and grooves
(also to the end of any piece that will be adjacent to
the house) and installing it while the paint is still
wet. This procedure not only assures an effective seal
against moisture penetration, but also provides a good
bond between floor boards.
Unlike interior flooring, T&G porch
flooring is fastened directly to the floor joists. No
additional nailing base is needed. A minimum 1/2" expansion
space is maintained between the flooring area and house
(or wall) to allow for dimensional change. This space
can be concealed with decorative exterior trim (also
acclimated).
Each piece of flooring is blind-nailed
at every joist, using hot-dipped galvanized 8d ring-shank
nails. Extend floor to create a 1" overhang beyond the
band joist.
Upon completion of the flooring installation,
two coats of the oil-based porch enamel to the surface
and exposed ends is recommended. Solid-color stains should
never be used on a porch floor due to their low resin
content.
To maintain the optimum performance
of a porch following proper design, material specification,
installation and finishing, a regular maintenance program
should be undertaken. Inspection for water accumulation,
integrity of the soil barrier, and any raised fasteners
are just a few items to include in a periodic examination
of the structure. Take necessary corrective action as
soon as possible. Refinishing porch flooring can be expected
every 3 to 5 years, depending upon weather conditions
and the amount of exposure to direct sunlight.
Attention to proper porch design is
as important to the longevity of the structure as are
the details of porch flooring specification and installation.
Inadequate air circulation beneath the porch and trapped
moisture between framing components will greatly reduce
the serviceability and long-term appearance of the porch.
The following recommendations are
key elements to the proper design and construction of
a fully-covered porch:
• Slope the exposed soil underneath the porch away from the center to permit
runoff of any water that may accumulate.
• To reduce the upward migration of moisture from the exposed soil
beneath the porch, cover with a moisture barrier (4-mil polyethylene is acceptable),
leaving two feet of exposed soil inside the perimeter of the porch. Anchor edges
of this barrier with gravel.
• Encourage air flow beneath the porch by using ornamental vents or lattice
skirting.
• Slope the porch framing 1/4" per foot away from the house to permit adequate
water runoff.
• Vent columns and newell posts at top and bottom.
• Check with your local building code department to be sure all code requirements
are satisfied within your porch design.
Article courtesy of Southern
Pine
If you'd like to learn more about SFPA,
visit our web sites at
www.sfpa.org/
www.southernpine.com
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