How to Guide

Wall Construction
ENGINEERED WOOD CONSTRUCTION GUIDE
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FORM NO. B360P
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© 2011 APA – THE ENGINEERED WOOD ASSOCIATION
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WWW.APAWOOD.ORG
55
APA Rated Siding Patterns and Grades
APA RATED SIDING, including 303 plywood siding, is available in a wide variety of surface textures and patterns. For
descriptions of siding surface patterns and thicknesses, refer to APA Product Guide: APA Performance Rated Sidings, Form
E300. Actual dimensions of groove spacing, width and depth may vary with the manufacturer. Where the charac teristics
of a particular wood species are desired, specify by grade and species preference.
In order to help specifiers select the
most appropriate siding appearance
for any particular job, APA 303 ply-
wood sidings are also identified by a
face grading system. There are four
basic siding classifications within
the system – Special Series 303,
303-6, 303-18 and 303-30. Each
class, as shown in Table 26, is fur-
ther divided into grades according to
categories of repair and appearance
characteristics.
Finishing Plywood
for Exterior Exposure
Care and Preparation
Plywood should be stored and
handled with care to avoid dam-
aging before finishing. Storage in
a cool, dry place out of sunlight
and weather is best. If left out-
doors, straps on bundles should be
loosened or cut and the plywood
covered. Allow good air circulation to prevent moisture condensation and possible mold growth.
Edge Sealing
Moisture enters the end grain of plywood or other wood-based products faster than through the surface. Consequently,
edges and ends of APA RATED SIDING panels or lap siding should be sealed. Although edge sealers are not necessar-
ily moisture-proof or permanently durable, they help to minimize sudden changes in moisture content in the siding,
due to weather.
APA RATED SIDING may be edge sealed at the factory. If the siding is not factory-sealed, it can be sealed quickly at the
job site while the panels or lap siding pieces are still in a stack. Edges or ends cut during construction should be resealed.
Siding to be finished with a semi trans parent or solid-color stain can be edge sealed with a liberal application of a paintable,
water-repellent sealer. If the siding is to be painted, apply sealer to edges using the same paint primer that will be used on the
surface. Horizontal edges, particularly lower drip edges of siding, should be carefully edge-sealed because of their greater
wetting exposure.
TABLE 26
APA 303 SIDING FACE GRADES
(a)
303 Series Type of Patch
Plywood Siding
Grades Wood Synthetic
303-OC Not permitted Not permitted
303-OL Not applicable for overlays
303-NR Not permitted Not permitted
303-SR Not permitted Permitted as
natural-defect shape
303-6-W Limit 6 Not permitted
303-6-S Not permitted Limit 6
303-6-S/W Limit 6 – any combination
303-18-W Limit 18 Not permitted
303-18-S Not permitted Limit 18
303-18-S/W Limit 18 – any combination
303-30-W Limit 30 Not permitted
303-30-S Not permitted Limit 30
303-30-S/W Limit 30 – any combination
(a) All panels except 303-NR allow restricted
minor repairs such as shims. These and
such other face appearance charac-
teristics as knots, knotholes, splits, etc.,
are limited by both size and number in
accordance with panel grades, 303-OC
being most restrictive and 303-30 being
least. Multiple repairs are permitted only
on 303-18 and 303-30 panels. Patch size
is restricted on all panel grades.