Section Contents

Understanding APA Trademarks for OSB

 APA Rated Sheathing

Rated Sturd-I-Floor (Single Floor Grade)



Structural I Rated Sheathing


OSB Panel Terminology

Panel grade

APA OSB panels are Performance Rated i.e. engineered for specific end applications in construction.  As such, the panel grade indicates the application for which they are intended e.g. Rated Sheathing, Rated Sturd-I-Floor.

The six overall requirements that OSB Performance Rated Panels must meet for construction applications means that they are also extremely suitable for many industrial and do-it-yourself (DIY) applications as well.

Span Rating 

For Rated Sheathing and Rated Sturd-I-Floor, the Span Rating applies when the long panel dimension or strength axis is across two or more supports.

The appearance of the Span Rating takes the form of a fraction such as 32/16, in rated sheathing panels. The left hand number denotes the maximum centre to centre spacing of supports (in inches) when the panel is used for roof sheathing (sarking), while the right hand number denotes the maximum centre to centre spacing when the panel is used for subflooring.

Sheathing panels with a roof Span Rating of 24 or greater may be used vertically or horizontally as wall sheathing over studs at 24 inch centres.  Those with roof Span Ratings of less than 24 inches may be used vertically or horizontally over studs spaced at 16 inches on centre.

Some panels are designated with a Span Rating of Wall-16 or Wall-24 which means that they have been specifically manufactured for use as wall sheathing over studs spaced at the designated distance apart.

APA Rated Sturd-I-Floor panels are designated specifically for single layer flooring applications where a solid face is required.  They are manufactured with Span Ratings of 16, 20, 24, 32 and 48 o.c.

Allowable uniformly distributed live loads at maximum span for Rated Sturd-I-Floor and Rated Sheathing is 100 lb/ft2 (1.48 kN/m2) for floors plus 10 lb/ft2 (0.15 kN/m2) dead load (65 lb/ft2 (0.97 kN/m2) total load for Sturd-I-Floor 48oc) and 30 lb/ft2 (0.45 kN/m2) snow load for roofs (35 lb/ft2 (0.52 kN/m2) for Rated Sheathing 48/24 or greater) plus 10 lb/ft2 (0.15 kN/m2) dead load.  Higher live loads can be achieved by placing the supports closer together than the maximum span indicated on APA trademarks.

Exposure Durability Classification or Bond Classification 

Bond classification relates to moisture resistance of the glue bond and thus to structural integrity of the panel. Bond classification of the panel does not relate to physical (erosion, ultraviolet etc.) or biological (mould, fungal decay, insect etc.) resistance of the panel.

Exposure 1 panels are manufactured with the same adhesive as used in exterior plywood panels, however, these OSB panels are not suitable for long-term exposure to the weather.  They are intended to resist the effects of moisture due to construction delays, or other conditions of similar severity.

Exposure 1 OSB panels are equivalent to the OSB/2 classification for load bearing panels for use in dry conditions as given in EN 300: Oriented Strand Boards (OSB) – Definitions, classification and specifications.  They will not be adversely affected by moisture under internal conditions of Service Class 1 or 2 environments as defined in Eurocode 5.

Thickness and Performance Category

The manufacturer’s stated thickness of a Performance Rated OSB panel is shown as a decimal figure (0.451 IN) in inches. The thickness of the panel is associated with the Performance Category which is linked to the nominal panel thickness e.g. 15/32 CATEGORY.  The thickness of the OSB panel has to be within the minimum and maximum thickness specification for the designated Performance Category.  Both the thickness and the Performance Category are displayed on the panel.  See also Performance Category.

Mill Number 

This is a unique APA code number awarded to each producing mill.

Performance/Product Panel Standards

APA OSB panels are manufactured to two US standards:

  • US Voluntary Product Standard PS 2-10, Performance Standard for Wood-based Structural-Use Panels. (The last two digits denotes the year in which the standard was approved).
  • PRP 108 – APA Performance Standards and Qualification Policy for Structural-Use Panels.

Sized for Spacing

This indicates that the panel has been manufactured to dimensions that help accommodate recommended panel end and edge spacing when installed.

  • Panels measure 96” (nominally 2440mm) x 48” (nominally 1220mm) and have a plus 0, minus 3mm (1/8”) tolerance.
  • Spacing between ends and edges of adjacent panels helps prevent buckling caused by moisture absorption.  The recommended spacing between panels is 3mm (1/8”) at both the end and edge joints, unless otherwise recommended by the manufacturer.

Tongue and Groove (T&G)

The appearance of T & G or Tongue and Groove within the APA trademark indicates that the panel has a tongue and groove profile on its two long edges which is to an APA approved pattern.

  • This eliminates the need for support (blocking) under adjacent panel edges to prevent them from deflecting independently of each other when load is applied.
  • The material removed to create the tongue normally reduces the width of the panel by approximately 12.5 mm (1/2”), therefore, the net width of the panel may be 47-1/2” (1206 mm).

Structural I

The term ‘Structural I’ appearing in an APA trademark indicates that the OSB structural-panel meets the requirements of a Performance Rated panel, except that Structural I panels meet additional requirements under Performance Standard US PS 2 for cross-panel strength and stiffness in bending and for racking load performance.