ARCHITECTS, DESIGNERS &
SPECIFIERS

Exterior use covers a wide range of applications, from sheltered soffits and roof decking to fully exposed cladding, fascias and signboards.

Two key exposure categories are recognised:

Protected exterior applications – Such as sheathing, soffits and roof decking, where exposure to moisture is limited. These are typically classified as Use Class 2/ Service Class 2 and require plywood suitable for humid conditions (EN 636-2).

 

Fully exposed exterior applications – such as cladding, fascias and exterior doors, where the plywood is regularly exposed to rain and weather. These are typically classified as Use Class 3/ Service Class 3 and require plywood suitable for exterior conditions (EN 636-3).

Factors affecting exterior plywood performance include rain, fluctuating humidity, sunlight, fungal attack, and in some cases frost, insects and chemical pollution.

A key consideration is edge protection. Plywood edges contain exposed end grain that can absorb moisture quickly. If left unsealed, water ingress can lead to staining, mould growth, paint failure, veneer separation and ultimately decay. Proper edge sealing is therefore essential to maintain durability and service life, particularly as water often enters faster than it can escape and may become trapped behind finishes.

Plywood manufactured for construction purposes is specified in accordance with EN 636. Products claiming compliance with this standard must also carry the specified markings, which includes a reference to EN 636. This standard was originally in three parts, but was reissued in a single part as follows:

The most recent edition of EN 636 retains the designations -1, -2 and -3 from the previous three part standard to represent dry, humid or exterior conditions of use.

These conditions are defined according to the parameters laid down for Use Classes in BS EN 335 durability of wood and wood-based products. Use classes: definitions applicable to solid wood and wood-based products.

Dry conditions: For interior applications with no risk of wetting, defined in Use Class 1, with a moisture content corresponding to environmental conditions of 20°C and 65% relative humidity.

Humid Conditions: For use in protected exterior applications as defined in Use Class 2, with a moisture content corresponding to environmental conditions of 20°C and 85% relative humidity.

Exterior Conditions: For use in external applications, as defined in Use Class 3, where the moisture content will frequently be above 20%.

EN 636 also introduces bending strength and modulus classes based on bending tests to EN 310. These give a designated strength (F) and modulus (E) parallel and perpendicular to the face grain. An example designation would therefore be F10/20. E30/40.

EN 636 gives minimum values for each of the classes and EN 12369-2 gives corresponding characteristic values for use with each of these classes.

Plywood for use in construction must demonstrate compliance with the Construction Products Regulation (CPR). The most straightforward route to achieving this is by demonstrating compliance with EN 13986, and therefore must carry a CE mark.

Plywoods are produced with glue bonds which range from those suitable for interior uses only, to those which will withstand full exposure for long periods.

BS EN 314-2 Plywood bonding quality. Requirements define three classes on the basis of test requirements that the plywood must meet:

Class 1: Dry conditions (interior, dry uses).

Class 2: Humid conditions (protected external service, ‘damp’ internal uses and limited exposure during construction).

Class 3: Exterior conditions (exposure to weather over substantial periods or continuous exposure to relative high humidity).

Full Exterior Bonding 

Class 3 bonds are a requirement for plywood to comply with BS EN 636-3. The bonds are largely comparable with what were known as WBP- weather and boil-proof bonds (to BS 6566 Part 8, now withdrawn), expect that the requirement that effectively they be made with phenolic-type glues has now been dropped. To qualify, the bond must now meet the stipulated test requirements.

Hanson Plywood offer a full and comprehensive guidance service to ensure that correct products are used for all applications. The information on panel products can be quite limited in many educational courses relating to architecture and design. This is why we are happy to provide assistance with specification for any end use.

Backed by the RIBA, NBS Source is a digital platform that provides a unified source of high quality, enhanced, manufacturer product data that will integrate seamlessly into your specification.

Hanson Plywood is proud to form part of the Approved RIBA CPD Providers Network offering a unique and informative CPD entitled: PLYWOOD A DEFINITVE GUIDE TO SPECIFICATION

The seminar focuses on:

• The key features and origination of plywood within a global context.
• The legal and environmental framework that impacts on plywood specification
• The key aspects and variability of the plywood manufacturing process.
• The origination of Marine Plywood and the disconnect with current European Plywood Standards.
• The European Technical Standards that underpin robust plywood specification.
• The key features of the different birch plywood face grades available.
• Reaction to Fire European Standards applicable to plywood.
  

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  To book your CPD please call 01422 330444 to talk to our specification team