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Glossary of Terms
Acrylic Resin

An ingredient of water-base (latex) paints and stains. Synthetic resin with excellent weathering characteristics. Acrylics can be colorless and transparent, or pigmented.

Air-Dried
See SEASONING
APA - The Engineered Wood Association
The trade organization representing most of the nation's structural wood panel manufacturers. The Association has three main functions: 1) research to improve plywood and other panel products and systems, 2) quality inspection and testing to assure the manufacture of high quality panel products, and 3) promotion of panel products and building systems.
APA Glued Floor System
A floor system developed by APA in which a single layer of APA RATED STURD-I-FLOOR panels (or subflooring in the case of double-layer construction) is glue-nailed to wood joists. The bond is so strong that floor and joists behave like an integral unit, greatly increasing floor stiffness and greatly reducing floor squeaks and nail popping. Only construction adhesives conforming to APA specification AFG-01 are recommended for use with the system.
APA Performance Rated Panels®
Panel products developed by APA, such as APA RATED SHEATHING, APA RATED STURD-I-FLOOR and APA RATED SIDING, designed and manufactured to meet performance criteria for specific end-use applications. APA Performance Rated Panels can be manufactured as conventional veneered plywood, as composites (veneer faces bonded to reconstituted wood cores), or as mat-formed panels (including waferboard and oriented strand board.) The trademarks on APA Performance Rated Panels include a Span Rating denoting the maximum recommended spacing of supports over which the panel should be placed for the designated end use, and the exposure durability classification of the panel.
APA Rated Sturd-I-Floor®
An APA Performance Rated Panel designed and manufactured specifically for residential and other light frame single-floor (combined subfloor-underlayment) applications for use under carpet. APA RATED STURD-I-FLOOR can be manufactured with Span Ratings of 16, 20, 24, 32 and 48 oc, in thicknesses ranging from 19/32 to 1-1/8 inch, and in three exposure durability classifications - Exterior, Exposure 1 and Exposure 2. Panels are available with either square edges or tongue-and-groove edges as specified. APA RATED STURD-I-FLOOR 48 oc plywood, commonly called 2-4-1, is also used in heavy timber roof construction.
APA Rated® Sheathing
An APA Performance Rated Panel designed and manufactured specifically for residential and other light frame wall sheathing, roof sheathing and subflooring applications. APA RATED SHEATHING can be manufactured with Span Ratings of 12/0, 16/0, 20/0, 24/0, 24/16, 32/16, 40/20 and 48/24, in thicknesses ranging from 5/16 to 3/4 inches, and in three exposure durability classifications—Exterior, Exposure 1 and Exposure 2.
APA Rated® Siding
A grade designation covering APA proprietary siding products. Commonly used, in addition to siding, for fencing, soffits, wind screens and other exterior applications. Can be used for interior paneling. Can be manufactured as conventional veneered plywood, as a composite or as oriented strand board siding. Both panel and lap siding are available. Special surface treatment such as V-groove, channel groove, deep groove (such as APA Texture 1-11), brushed, rough sawn and texture-embossed (MDO). Span Rating (stud spacing for siding qualified for APA Sturd-I-Wall applications) and face grade classification (for veneer-faced siding) indicated in trademark.
APA Trademark
APA is an approved quality supervision and testing agency for softwood plywood and structural wood panels. Typical trademarks of APA member-manufactured products are shown throughout these courses. Some engineered wood products bear the APA EWS trademark. Engineered Wood Systems is a related corporation of APA.
Batten
A thin, narrow strip of plywood or lumber used to conceal or protect a joint between adjoining pieces of lumber or plywood.
Beam — Normally a horizontal or sloping member of glulam that is designed to carry vertical loads.
Beam
Normally a horizontal or sloping member of glulam that is designed to carry vertical loads.
Simple Span: a member that is supported at both ends.
Continuous: a single member which is supported at more than two bearing locations.
Cantilever: a member which has one or both supports away from the ends; one of which overhangs its support.
Bearing Stress
The compressive stress exerted on an external surface of a member. This stress is commonly the stress occurring at a point of support, such as at a beam hanger.
Bending Strength
The ability of a member, such as a beam, to resist the tendency to break when exposed to external forces such as roof or floor loads. The strength is achieved by the resisting couple action of the tension and compression stresses at the top and bottom of the beam.
Bevel
To cut panel edges or ends at an angle to make smooth mating joints between panels.
Blister
See BLOW or DELAMINATION
Blister Detector
See BLOW DETECTOR
Blocking
Light lumber strips nailed between major framing members to support edges of structural panels where they meet.
Blow
 localized delamination caused by steam pressure buildup during the hot pressing operation. The steam may result from high moisture content of the veneer or wood composite, excessive glue spread, or high press temperatures.
Blow Detectors
Systems that detect delaminations in engineered wood panels by sending ultrasound through the panel vertical to the surface and measuring the change in ultrasonic conductivity.  Also known as Blister Detectors or Delamination Detectors
Bond
To glue together, as veneers are "bonded" to form a sheet of plywood. Pressure is applied to keep mating parts in proper alignment. Most glues used in panel manufacture require both heat and pressure to cure properly.
Bond Classification
Exposure ratings for APA structural wood panels designated in APA trademarks as Exterior, Exposure 1, Exposure 2, or Interior.
* 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 long construction delays may be expected prior to providing protection, or where high moisture conditions may be encountered in service. 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.
* Exposure 2 panels (identified as Interior type with intermediate glue under PS 1) are intended for protected construction applications where only moderate delays in providing protection from moisture may be expected.
* Interior panels or panels which lack further glueline information in their trademarks are manufactured with interior glue and are intended for interior applications only.
Bow
Distortion of a structural wood panel so that it is not flat lengthwise. - See also CUP
Bundle
A unit or stack of wood panels held together for shipment with bands. Stack size varies throughout the industry, with the average stack running about 30 to 33 inches high. A bundle 30 inches high, for example, contains 120 sheets of 1/4-inch panels, 80 sheets of 3/8-inch panels, or 60 sheets of 1/2-inch panels.
Butt Joint
The joint formed when two parts are fastened together without overlapping. For end-to-end joints, use a nailing strip. For corner joints, nail directly into panel if it is at least 3/4-inch thick. If panel is thinner than 3/4-inch, use a reinforcing block.
Center (Centers)
Inner ply or plies of a plywood panel whose grain runs parallel with that of the face and back plies.
Center Gap
See CORE GAP
Chipboard
See PARTICLEBOARD
Chord
Any of the outside members of a truss connected and braced by web members. Also, may refer to perimeter members of a panel diaphragm.
Circular Plug
See REPAIRS
Column
Normally a vertical member that is designed to carry loads from a beam:
Concentrically Loaded: when the resultant load acts parallel to the axis of the member and is applied at its centerline.
Eccentrically Loaded: when the resultant load acts parallel to the axis of the member but is applied away from its centerline such as along its side.

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