Essential:

• Racking
• Bending strength
• Bending stiffness
• Bond quality
• Durability – moisture resistance
• Release of formaldehyde
• Strength & stiffness for structural use
• Impact resistance for structural use

Depending on specification:

• Reaction to fire
• Water vapour permeability
• Airborne sound insulation
• Sound absorption
• Thermal conductivity
• Mechanical durability
• Biological durability
• Content of pentachlorophenol
• Embedment strength

More on the standards required for determining plywood panel performance characteristics for these applications.

APA’s system of span ratings denotes the maximum centre to centre spacing of supports (in inches) over which the plywood should be installed with its long dimension placed across the supports. This makes it easier to match the correct plywood panel to the specific spacing, whether studs in the wall construction, or the distance apart of the supports for normal domestic roof loadings.

When a panel is marked with one of two specific span ratings, Wall-16 or Wall-24, this tells you that it has been made specifically for use as wall sheathing. While all APA panels carry a span rating when suitable for roofing applications. This is not always the case for walls. Normal construction has the stud spacing of wall sections at either 16” (406mm) or 24” (610mm) centres. For wall sheathing use, panels with a roof span rating of 24 or greater may be installed vertically or horizontally as wall sheathing over studs spaced at 24” (610mm) on centre.

Those with roof span ratings of less than 24 may be installed vertically or horizontally over studs spaced at 16” (406mm) on centre. Where panels are fixed horizontally across studs, it will be necessary to block the unsupported paned edges between the studs.

For 3/8” (9mm) – usually 24/0 but Wall-16 or Wall-24 also possible.
For 7/16” (11mm) – usually 24/16 but also Wall-24.

Click here for more on plywood performance and thickness guidance.

The combined design live load plus dead load is 25 lbs/ft2 (1.195kN/m2).

Fixing should be placed 6” (150mm) apart around the panel edges and 12” (305mm) apart on intermediate supports.
Fixings should be positioned 3/8” (9mm) from the panel edges.

Plywood expands and shrinks slightly and when the panels are butted together tightly, the only way they can expand is to dish upwards or downwards. To allow for this, APA advises that a space of at least 1/8” (3mm) is left between panel edges. This may need to be increased if there is actual wetting of the panels.

• Before you order, check if the wall sheathing would be affected by direct wind load. If it is, refer back to the designer.
• Determine if you need Exterior or Exposure 1 plywood. (click here for help to decide)
• The distance apart of the centre line of the studs. – see span rating advice.
• Ensure that only one thickness of plywood is received with the same span rating.
• The number of panels required.

Essential:

• Bending strength
• Bending stiffness
• Bond quality
• Durability – moisture resistance
• Release of formaldehyde
• Strength & stiffness for structural use
• Impact resistance for structural use
• Strength & stiffness under point load for structural use

Depending on specification:

• Reaction to fire
• Water vapour permeability
• Airborne sound insulation
• Sound absorption
• Thermal conductivity
• Mechanical durability
• Biological durability
• Content of pentachlorophenol
• Embedment strength

More on standards required for determining plywood panel performance characteristics for these applications.

APA’s system of span ratings denotes the maximum centre to centre spacing of supports (in inches) over which the plywood should be installed with its long dimension placed across the supports. This makes it easier to match the correct plywood panel to the specific spacing, whether studs in the wall construction, or the distance apart of the supports for normal domestic roof loadings. All APA panels carry a span rating when they are suitable for roofing applications but this is not always the case for walls.

To enable the roof to carry the design load, you need to know the distance apart of three main roof sheathing supports. Knowing the span rating helps you match the panel to the distance between these supports. Supports placed too far apart will weaken the structure while those placed closer together can enhance the load that can be carried.

The span rating shown on the APA trademark indicates that the plywood panel can carry a uniformly distributed load of 50 lbs/ft2 (2.393kN/m2) domestic loadings.

APA trademarked panels will always show the specific span rating. It denotes this as a fraction, for example 32/16 for dual purpose panels suitable for both roofing and sub-flooring. The left-hand number is the relevant one – giving the centre to centre spacing of supports (eg 32 “) for roofing applications. (The right-hand number refers to sub-flooring applications).

The uniform deflection limit is L/180 (where L is the span) under a combined live load of 35 lbs/ft2 (1.676 kN/m2) plus a dead load of 15 lbs/ft2 (0.718 kN/m2) and L/240 under live load only. This represents one third of the load the panel has to pass to meet the requirements of PS2. These loadings assume the panel is laid continuously over two or more supports with the long dimension or strength axis across supports.

This will enable a higher uniformly distributed load to be accommodated. Recommended uniform live loads for APA Rated Sheathing can be found in Table 30 of the APA publication Engineered Wood Construction Guide (download here). It is advisable to check if other parts of the construction can also carry any increased load without any changes in design.

This will have several effects on the construction:

• The roof will carry less dynamic load for the required deflection requirement.
• The dead load weight will be detrimentally compromised.
• The deflection between supports will increase and could well be outside the permitted deflection allowance permitted in the product standard PS2.
• This will give an uneven shape with ‘sagging’ between the supports.

For 3/8” (9mm) – usually 24/0 but 20/0 also available.
For 15/32” (12mm) & ½” (12.5mm) - usually 32/16 but also 24/0.
For 19/32” (15mm) & 5/8” (16mm) – usually = 40/20 but also 32/16.
23/32” (18mm) & ¾” (19mm) – usually 48/24 but also 40/20.

Click here for more on plywood performance and thickness guidance.

For normal use, fixings should be placed 6” (150mm) apart around the panel edges and 12” (305mm) apart on intermediate supports. Fixing also should be positioned 3/8” (9mm) from the panel’s edges. Ring shank nails are recommended to prevent pull out under the effects of wind uplift.

In areas liable to high winds the distance apart needs to be moved closer. APA recommends spacing at 4” (100mm) intervals around the perimeter of the plywood and every 6” (150mm) at intermediate supports.

All plywood expands and shrinks slightly. When the panels are butted together tightly, the only way they can expand is to dish upwards or downwards. To allow for this, APA advises that a minimum space of 1/8” (3mm) is left between panel edges. This may need to be increased if there is actual wetting of the panels.

• The distance apart of the centre lines for the supports.
• Check the designed live load and dead loads are within the permitted requirements for the panel being ordered.
• Ensuring that only one thickness of plywood is received with the same span rating.
• Deciding if you need Exterior or Exposure 1 plywood (click here for help to decide).
• The number of panels required.