APA > Products & Trademarks > Builders Tips – Walls & Roofing
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Using Plywood Sheathing for Walls and Roofing

Unsanded, plywood sheathing panels are specially designed for walls and roof applications. For its use in structural subfloor decking, see our Builders Tips on APA’s special flooring product, Sturd-I-Floor.

APA manufactures its sheathing panels to meet the requirements of US standard PS 2-18.  As long as mills comply with the main requirements, individual specifications can differ. Depending on where it will be used and the moisture content and exposure, you have the option of an Exterior or Exposure 1 panel grade.

Follow the trail below for more about sheathing, the importance of span ratings and the specific performance characteristics and standards that apply to roofing and walls for selling in the UK and EU (such as (BS) EN 314-2 for external bond classification).

You can click on all links, even those that appear grey, to refer back.

Click here for specific guidance on wall applications and relevant standards

Click here for specific fixing advice for roofing and relevant standards

What specific performance characteristics for walls are covered by UK and EU standards?

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.

What is span rating and how do I identify the right span rating for walls?

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.

How do I choose the right span rating for different thickness/performance categories?

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.

What engineering values are these wall sheathing panels calculated on?

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

What spacing do I use between fixings?

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.

Moisture is an issue for walls, how do I allow for panel expansion?

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.

What do I need to know when ordering plywood for wall sheathing?

  • 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.

What specific performance characteristics for roofing are covered by EU standards?

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.

What is span rating and why is it important for roofing?

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.

Is the span rating for roofing shown on an APA panel?

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).

What is the basis of the engineering values?

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.

What if I use a plywood panel on supports placed closer together than the designated span rating?

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.

What happens if the centre to centre spacing of the supports exceeds the designated span rating?

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.

How do I choose the right span rating for different thickness/performance categories?

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.

What spacing should I use between fixings?

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.

How do I allow for panel expansion due to moisture?

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.

What do I need to take into account when ordering plywood for roofing?

  • 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.

 

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All Questions OSBPlywood

What defines a product under UK and EU construction product regulations?

This applies to ‘any product or kit which is produced and placed on the market for incorporation in a permanent manner in construction works or parts thereof and the performance of which has an effect on the performance of the construction works with respect to the basic requirements for construction works.’

Products must clearly display the appropriate conformity marking and have the correct Declaration of Performance documentation  in line with either the UK-CPR or the EU-CPR. More

Tell me more about a Declaration of Performance

Manufacturers wishing to trade in the European market are legally required to set down the levels of performance for any construction product. They have to be listed in an official document called a Declaration of Performance. More.

The mark of approval stamped on a panel means it can legally be used – but which standards apply?

You can either check out the right standard for your application; or look at the standards that the trademarked panels comply with for different plywood grades – A-A, A-B, A-C; B-B, B-C; C-C, C-D – here.

 

 

What is the difference between a touch-sanded panel and sanded panel?

The veneer of  an APA trademarked panel must conform to one of the six grades listed in the US PS 1-19 standard: N, the highest classification (rarely produced), followed by A, B, C-plugged, C and D. Non-overlaid APA plywood panels come in three levels of surface finish – sanded, touch-sanded and unsanded. More.

Also see veneer grades for Popular APA Plywood Panels.

How do APA veneer grades match those in UK and EU standards

The main grades for APA’s structural plywood panels are: A-A, A-B, A-C, B-B, B-C;,C-C, C-D, D-D, Sturd-I-Floor, Underlayment, CC plugged, CD plugged. APA has a quick guide here to help you match the grades with the requirements of (BS) EN 635-3. Equivalents cannot be exactly compared as two different sets of grading rules apply.

I want to specify an APA panel for concrete formwork – what do I need to know?

Plyform is a type of panel with sufficient strength to support the weight of the wet concrete. APA offers three types, all using only the strongest wood species (groups 1,2 or 3) for the face and back veneers. They have an exterior bond classification and come in three strength classes – Structural 1, Class I or Class II.

See APA’s comprehensive Concrete Forming Design/Construction Guide for architects, engineers and contractors and the types of APA concrete forming plywood panels.

What plywood panels likely to be available in the UK & EU?

The main grades for APA’s structural plywood panels are:  A-A, A-B, A-C, B-B, B-C;,C-C, C-D, D-D, Sturd-I-Floor, Underlayment, CC plugged, CD plugged.  Non-overlaid APA plywood panels come in three levels of surface finish – sanded, touch-sanded and unsanded.  APA’s guide identifies each panel’s specific finish, veneer strengths and the wood species used, as well as bond durability.

 

What are the main European standards that I would need to be aware of for plywood panels?

The main standards are: EN 13986, EN 636, EN 314, EN 635-3.  And for more details, see EU standards for plywood.

The CE-mark on an APA plywood panel means it conforms to European Standards – but which ones?

Plywood Design Information looks at the plywood grades A-A, A-B, A-C; B-B, B-C; C-C, C-D and the relevant standards that the trademarked panels comply with.

 

How do APA veneer grades match those given in the European standards

APA has produced two easy to follow guides to help match the grade numbers given on a US finished plywood panel with the requirements of  EN 635-3.

Detailed guide listing permissible defects – with maximum sizes.

Simplified guide to the US PS 1-19 veneer grading rules and appearance grades in EN 635-3 based on the appearance of the surface veneers. Equivalents cannot be exactly compared as two different sets of grading rules apply.

I want to specify an APA panel for concrete formwork – what do I need to know?

See APA’s comprehensive Concrete Forming Design/Construction Guide for architects, engineers and contractors and the types of APA concrete forming plywood panels.

What are the main plywood panels likely to be available in Europe?

See APA’s guide to ‘Plywood Panel Grades for Specific Applications’

 

What are the main standards for plywood panels?

The main standards are: (BS) EN 13986, (BS) EN 636, (BS) EN 314, (BS) EN 635-3.  And see ‘Applications, Check your Standard‘.

What are the main changes to the FSC Chain of Custody Certification standard?

Download What’s New in FSC revised COC standard.   Also, the previous FSC compulsory verification programme has been replaced by a due diligence protocol with a new risk assessment system. Learn more. Good forestation practice in the US supports the aims of EUTR.  Its sustainably managed forests comply with one or more of the five leading certification agencies responsible for verifying proper forestry practices.

 

Can US certified EPDs be used for environmental performance ratings under the BREEAM system?

APA products can count towards a building’s BREEAM rating, learn how here.  The British Research Establishment and the US Underwriters Laboratories  now recognise each other’s certified EPD making it simpler for APA member mills to gain environmental performance ratings under the BRE Environmental Assessment Method  (BREEAM).

Does APA plywood meet the lowest category (E1) for formaldehyde release without need for further testing?

Under the harmonised European Standard for wood-based panels, EN 13986, Annex B, ‘wood-based panels glued with resins emitting either no formaldehyde or negligible amounts of formaldehyde after production as e.g. isocyanate or phenolic glue’ are to be classified as E1 (the lowest formaldehyde release class) without further testing.

See APA’s guide Formaldehyde and Engineered Wood Products.  APA plywood is designated under the lowest E1 category for formaldehyde release without needing further testing.  APA’s US PS 1 and PS 2 plywood have been tested to EN 717-1 and formaldehyde levels already meet the requirements for the E1 classification limit.

Also see:  Formaldehyde (plywood) and Formaldehyde (OSB).

 

 

Can APA plywood and OSB be used in non-construction applications?

US plywood and OSB are equally effective as sturdy, robust and cost-effective solutions  for non-construction applications – from shelving, site hoardings , protective linings in the cargo bay of delivery vehicles to packaging and furniture.   See APA’s Performance Panels.   Need help to decide what grade or type of panel to use for a specific application? APA’s Industrial Panel Selection Guide (Form T200) is another easy to use resource.

What are Use Classes and how do they equate with Service Classes?

For maximum biological durability, both Service Classes and Use Classes must be considered when specifying engineered wood panels. See APA’ s guide here.

Use Classes covering plywood and OSB have replaced ‘hazard classes’. They will also cover LVL when the LVL standards have completed their update. Use Classes are based on different environmental exposures that can make the panel susceptible to deterioration. The  in Eurocode 5 assign strength values and calculate deformation in load-bearing situations. They are determined by the moisture content of the panel corresponding to the environmental humidity and temperature during service.

How do APA’s member’s products count towards a sustainability assessment for new construction or in refurbishment projects?

The British Research Establishment and the US Underwriters Laboratories  now recognize each other’s certified EPD making it simpler for APA member mills to gain environmental performance ratings under the BRE Environmental Assessment Method  (BREEAM).  This is the UK’s leading and most widely used environmental assessment method for buildings and communities. It sets the standard for best practice in sustainable design and has become the de facto measure used to describe a building’s environmental performance. Learn how APA products can count towards a building’s BREEAM rating.

What is a ‘life cycle stage’ and how do these link to the environmental assessment of whole buildings?

A good starting point is our Green Topics section and  Types of EPD and the five life cycle stages

How do core category rules link with environmental product declarations?

EN 15804:2012 +A1:2013 provides the core Product Category Rules (PCR) for the production of Environmental Product Declarations (EPD) for all construction products and services.  Review with main environmental standards.  For more details see: Core Product Category Rules (PCR) for Products and Services. 

Whose responsibility is it to check that wood products being imported into the EU do not originate from illegally sourced timber supplies?

The European Union Timber Regulation (EUTR) puts specific obligations on operators and traders . Operators (or importers) are any (natural or legal) person first placing timber on the EU market. They must maintain records of any traders that they supply timber to.  They must implement a due diligence system to minimise the risk of putting illegal timber or any of its derived products on the market.  Learn more.

Does the EUTR require mills to provide any extra documentation for customs entry into the European Union?

The European Union Timber Regulation (EUTR) puts specific obligations on operators and traders and applies to timber originating in the domestic (EU) market, as well as from third (non-EU) countries such as  the US. The information it requires has to be retained for at least five years and be available on request.  See European Timber Regulation.

Must all plywood and OSB panels carry a CE marking?

Manufacturers of wood-based products  covered by either a harmonised European standard (hEN) or a European Technical Assessment (ETA) must apply for CE marking under the 2013 Construction Products Regulation.  See CPR & CE Marking  and our Official Guidelines section.

What is the definition of a construction product under the CPR?

This applies to ‘any product or kit which is produced and placed on the market for incorporation in a permanent manner in construction works or parts thereof and the performance of which has an effect on the performance of the construction works with respect to the basic requirements for construction works.’

Products must clearly display the CE mark and have the correct Declaration of Performance documentation.  For more info: CPR & CE Marking.

What is a Declaration of Performance referred to under the Construction Products Regulation?

Under the CPR, manufacturers wishing to trade in the European market are legally required to set down the levels of performance for any construction product.  They have to be listed in an official document called a Declaration of Performance.

What is the difference between Structural 1 and Exposure 1?

Exposure 1 is a glue bond classification.  It uses the same 100% waterproof glue as exterior panels and refers to a panel’s durability when long delays in construction are expected or when facing high moisture content. For plywood, see  https://apawood-europe.org/products-trademarks/plywood/trademarks/glue-bond/.  For OSB:  https://apawood-europe.org/products-trademarks/osb/trademarks/exposure-durability-classification/

Structural 1 refers to a panel’s superior performance characteristics.  For OSB, see https://apawood-europe.org/products-trademarks/osb/comparable-performance-requirements/

For Structural 1 plywood,  all panels have special improved veneer grades and if manufactured to the US PS1 standard, the veneer grades will be species with a Group 1 strength classification.  See group classification of species.

 

The CE-mark on an APA plywood panel means it conforms to European Standards – but which ones?

Plywood Design Information looks at the plywood grades A-A, A-B, A-C; B-B, B-C; C-C, C-D and the relevant standards that the trademarked panels comply with.

 

I want to use a Rated Sheathing panel for flooring/ roofing application, what info do I need to know?

For plywood, see Span rating.  For OSB, see Span rating. A full range of technical information in under Products and Trademarks.

What extra strength benefits do Structural 1 OSB panels provide over standard Rated Sheathing panels?

OSB Structural I  on an APA trademark indicates that the OSB structural-panel meets the requirements of a Performance Rated panel.  This delivers superior design capacity for these panels over OSB Rated Sheathing and Sturd-I-Floor.  Also see Comparison of Superior Design Capacities for OSB Structural I Sheathing with OSB Rated Sheathing.

What is the difference between a touch-sanded panel and sanded panel?

Veneer in a finished US trademarked plywood panel must conform to one of the six grades listed in the US PS 1-09 standard: N, the highest classification (rarely produced), followed by A, B, C-plugged, C and D.  Non-overlaid APA plywood panels come in three levels of surface finish – sanded, touch-sanded and unsanded.

Also see veneer grades for Popular APA Plywood Panels.

How do APA veneer grades match those given in the European standards

APA has produced two easy to follow guides to help match the grade numbers given on a US finished plywood panel with the requirements of  EN 635-3.

Detailed guide listing permissible defects – with maximum sizes.

Simplified guide to the US PS 1-19 veneer grading rules and appearance grades in EN 635-3 based on the appearance of the surface veneers. Equivalents cannot be exactly compared as two different sets of grading rules apply.

How do I correctly gauge the face appearance a plywood Siding panel?

See guide to selecting siding (cladding) with APA 303 siding panels.

I want to specify an APA panel for concrete formwork – what do I need to know?

See APA’s comprehensive Concrete Forming Design/Construction Guide for architects, engineers and contractors and the types of APA concrete forming plywood panels.

Are APA panels tongue and grooved on all four edges?

APA panels have a tongue and groove profile on their two long edges.  This eliminates the need for support (blocking) under adjacent panel edges to prevent them from deflecting independently of each other when load is applied.  See Tongue & Groove  (plywood) and Tongue & Groove (OSB).

I am not familiar with the term ‘Sized for Spacing’ – what is its significance?

‘Sized for Spacing’ on APA Rated Sheathing, APA Rated Sturd-I-Floor and APA Rated Siding trademarks indicates that the manufacturer has produced the panel to a size slightly less than the traditional nominal 2440mm (96″) by 1220mm (48″).  It is done to facilitate proper panel spacing during construction.  See Sized for Spacing  (plywood) and Sized for Spacing  (OSB).  For further technical details see Product and Trademarks.

How are Performance Category and thickness related?

Performance Category, Panel Thickness and Span Ratings are key categories that need to be considered together.  See Thickness, Performance Category  (plywood) and Thickness, Performance Category (OSB).

I’d like to know more about a panel’s Span Rating and how it links to thickness.

Plywood: Span rating
OSB: Span rating

What is Span Rating on the APA trademark and why is it important?

Span Rating denotes the maximum recommended centre to centre spacing of supports in inches over which the panel should be placed with its strength axis across two or more supports. Plywood: Span rating.  OSB: Span rating

What is the difference between Exposure 1 and Exterior plywood panels? What are their appropriate uses?

Bond classification relates to moisture resistance of the glue bond and therefore to the structural integrity of the panel.  See glue bond durability classification (plywood) and exposure durability (OSB).

What are the main OSB panels likely to be available in Europe?

See APA’s guide to panel grades  and also info on understanding the trademark.

What are the main plywood panels likely to be available in Europe?

See APA’s guide to ‘Plywood Panel Grades for Specific Applications’

 

What are the main European standards that I would need to be aware of for OSB panels?

The main standards are: EN 13986 and EN 300.   But also see the other relevant standards for OSB.

What are the main European standards that I would need to be aware of for plywood panels?

The main standards are: EN 13986, EN 636, EN 314, EN 635-3.  And for more details, see EU standards for plywood.