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Plywood

pine plyFrom a green perspective, there are a couple of major problems with the use of plywood

  • It is not manufactured in the UK so has to be imported, with the associated problems of international transport which increases embodied energy and creates pollution.
  • A considerable part of plywood production has devastated native forests, especially in the ‘far east’. This has been particularly serious in Indonesia. Currently a lot of ply is coming in from Brazil and though much of it claims to be sustainably sourced it is important to look for the FSC or PEFC accreditation marks.

A quick web search for ‘far eastern ply’ will bring up a few dozen companies supplying it but only a few will have any kind of environmental policy on procurement. Those that do, fall into two groups
  • those with a clear statement concerning the supply of FSC and PEFC certified timber.
  • those with a fuzzy sort of statement about respecting the environment and providing products ‘wherever possible’ from sustainable sources.
Generally the environmental problems occur with hardwood ply because the softwood ply is mostly sourced from the Baltic countries, Scandinavia, Canada or the US where sound environmental policies are mainly already in place.
Russia supplies most of the birch ply and once again, the accreditation marks should be showing.
Greenpeace have recently come out with a report about how unsustainable much of the plywood is that is imported into the UK, and how OSB is an excellent alternative, especially for floors and roof decking. See OSB
There are several situations where it may not be possible to substitute OSB for ply.
  • where WBP or marine grade ply is specified since OSB cannot be made waterproof.
  • where ply is being used for its racking strength such as in certain timber frame situations. A structural engineer will be able to advise on this.
  • where thin birch ply is used for creating curved surfaces.

Grades of plywood

As with timber generally the grading of ply varies somewhat depending on the country of origin. The grading mainly concerns the durability of the timber used, the visual quality of wood used on the faces,  the type of glue used to stick the layers together, the structural strength and the amount of harmful emissions from the chemicals used in the adhesive. There are now EN standards in place to cover these qualities.

However you still find quite a lot of ply with the older type of markings. These vary somewhat, depending on the country of manufacture but are generally of the A/A (two excellent faces),  A/B (one excellent face and the other reasonable),  B/B,  B/C,  C/C etc. format. An added X means exterior grade.  WBP / means Weather and Boil Proof. Marine grade is extremely durable and can remain in contact with water for long periods.

The relatively new Eurocodes are as follows:

Durability of the timber EN 636

EN 636 has three grades:

  • EN 636-1  for use under dry interior conditions
  • EN 636-2  for use where there are humid conditions such as in cold roof or floor areas or, if used externally it should have some form of cover or protection from rain etc.
  • EN 636-3 for use where it is fully exposed to the weather.

The bond quality of the adhesive used

EN 314-2 covers the bond quality:

  • Class 1   is for structural interior conditions which are dry
  • Class 2   is for structural external conditions with short periods of exposure to the weather or high humidity
  • Class 3   is for structural uses capable of withstanding exposure to weathering conditions and liquid water over sustained periods of time. (This is the grade which was known as WBP – Weather and Boil Proof and you sometimes still find this marking)

Appearance

BS EN 635-3 : Plywood – Classification by surface appearance -softwood

There are 5 grades:  E, I, I/II, II/III, and IV (with E being the best with virtually no flaws and IV being the worst with almost no restrictions on the quality of the surface)

This subject gets quite complicated and it’s best to view the EN standards especially if you are trying to compare with the old British Standards. See 9. BS EN 635-3 : Plywood – Classification by surface appearance. If you are intending to leave ply exposed as a decorative finish it pays to go and select the sheets yourself.

Structural strength

The bending strength and stiffness may well be important factors and the TRADA page ‘Specifying wood based panels for structural use‘ gives the relevant standards to look for. In the case of racking strength, a structural engineer will normally specify what is required. See also Compliance for APA Plywood in Europe

Chemical emissions

Due to concerns over emissions of formaldehyde, Emission class E1 became obligatory for panel production of EPF European Panel Federation members in 2005.

1 comment to Plywood

  • Russell Bateman

    Many thanks for clearly set-out and un-ambiguous facts about the essentials for specifying plywood

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