From 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 energythe total amount of energy it takes to make a material (or a building). See more on 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 FSCForest Stewardship Council (who accredit timber) see their database or PEFCProgramme for the Endorsement of Forest Certification. See their web site accreditation marks.
- 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.
- 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)
BSBritish Standard 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.
The bending strength and stiffness may well be important factors and the TRADATimber Research and Development Association A trade association with a strong reputation for research and publication on all things timber 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
Due to concerns over emissions of formaldehyde, Emission class E1 became obligatory for panel production of EPF European Panel Federation members in 2005.