| Exposure Durability APA trademarked panels may be produced in four exposure
durability classifications - Exterior, Exposure 1, Exposure 2, and Interior. The exposure
durability classification relates to glue bond, and thus to structural integrity of the
panel. Since aesthetic (nonstructural) attributes of panels may be compromised to some
degree by exposure to weather (b), installation recommendations in this publication are
designed to provide optimum overall performance.
NOTE: Exposure durability classification
relates to moisture resistance of the glue bond land does not relate to
fungal decay resistance of the panel. Fungal decay of wood products may occur when the
moisture content exceeds 20% for an extended period. see APA Technical Note R495,
Controlling Decay in Wood Construction, for a discussion of fungal decay. Prevention of
fungal decay is a function of proper design, material specification, construction and
maintenance of the structure. While this publication includes many of the applicable
provisions, reference to local building codes and other design documents is also
necessary.
Exterior panels have a fully
waterproof bond and are designed for applications subject to permanent exposure to the
weather or to moisture.
Exposure 1 panels have a fully
waterproof bond and are designed for applications where construction delays may be
expected prior to providing protection. Exposure 1 panels are made with the same exterior
adhesives used in Exterior panels. However, because other compositional factors may affect
bond performance,only Exterior panels should be used for permanent exposure to the
weather.(c)
NOTE: Plywood APA Rated Sheathing Exposure
1, sometimes called "CDX" in the trade, is occasionally mistaken as an Exterior
panel and erroneously used in applications for which it does not possess the required
resistance to weather. "CDX" should only be used for applications as outlined
under Exposure 1 above. For sheathing grade panels that will be exposed permanently to the
weather, specify APA Rated Sheathing Exterior (C-C Exterior plywood under PS 1).
Exposure 2 panels (identified as
Interior type with intermediate glue under PS 1 ) are intended for protected construction
applications where potential for conditions of high humidity and short-term water leakage
exist.
Interior panels which lack
further glueline information in their trademarks are manufactured with interior glue and
are intended for interior applications only.
Group Number
Plywood can be manufactured from over 70 species of wood.
These species are divided on the basis of strength and stiffness into five Groups under
Voluntary product Standard PS 1.
Strongest species are in Group 1; the next strongest in
Group 2 , and so on. The Group number that appears in the trademark on some APA
trademarked panels- primarily sanded grades-is based on the species used for face and back
veneers. Where face and back veneers are not from the same species Group, the higher Group
number is used, except for sanded panels 3/8 inch thick or less and Decorative panels of
any thickness. These are identified by face species because they are chosen primarily for
appearance and used in applications where structural integrity is not critical. Sanded
panels greater than 3/8 inch are identified by face species if C or D grade backs
are at least 1/8 inch and are no more than one species group number larger. Some species
are used widely in plywood manufacture; others rarely. Check local availability if a
particular species is desired.
(b) Panel surfaces may become uneven and irregular under
prolonged moisture exposure. Panels should be allowed to dry, and panel joints and
surfaces may need to be sanded before applying some finish materials.
(c) Exposure 1 panels may also be used when exposure to the
outdoors is on the underside only, such as at roof overhangs. Appearance characteristics
of the panel grade should be considered. |
