Plywood classes explained
We look at the different classes of plywood, class 1, 2 and 3, and explain the differences.
Plywood undergoes strict testing on bonding and durability to prove that it is worthy of usage within the construction industry.
There are 2 standards, known as “harmonised standards”, that work together to determine which plywoods can be used under different conditions:
- EN314-2 (bonding quality)
- EN636 (durability & bonding)
These tests then determine the class that plywood can be specified under and what they can be used for.
Elliotts Timber Product Manager, Pat Collins, explains how these harmonised standards work.
Plywood bonds and specifications
Plywood bonds – EN314-2
Plywoods are produced using bonds. The types of bonds used are based on whether the plywood is for use in dry, humid or exterior conditions.
The BS EN314-2 Plywood bonding quality requirements define three classes on the basis of test requirements that the plywood bond must meet:
| Class | For use in |
|---|---|
| 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 expire to relatively high humidity). |
These classes are determined by laboratory tests in which different plywood boards are subjected to simulated weather conditions. The integrity of the plywood bonds after the tests will determine it’s bond class.
Plywood specifications – EN636
Following on from the EN314-2 tests, plywood boards are required to comply with one of the three performance classes within EN636 for use in construction. This takes into account the quality of the bond and the durability of the timber species used.
The requirements for each class are as follows:
| What are you using the plywood for? | EN | Usage class | Where can this plywood be used? | Where to buy |
|---|---|---|---|---|
| Plywood for use in dry conditions | EN636-1 | Class 1 – This class is appropriate for normal interior climates. | Warm roofs, intermediate floors, internal timber frame and partition walls. | From your local branch |
| Plywood for use in humid conditions | EN636-2 | Class 2 – This class is appropriate for protected external applications, it is also suitable for interior situations where the service moisture content is raised above the Class 1 level. | Cold roofs, ground floors and external timber frame walls. | Visit your local branch |
| Plywood for use in exterior conditions | EN636-3 | Class 3 – This class is designed for exposure to weather over sustained periods. | Fully exposed service conditions. | From your local branch |
And don’t forget…
Just like all other timber-based products, it is vitally important that plywood specified for use in humid and or exterior conditions receives an appropriate protective finish to all faces and edges. This minimises moisture getting into the plywood and prolongs it’s life.
Getting the right plywood for your project
It is vital to specify and purchase plywood that is suited to job you are using it for, based on the classes above. For example:
- If you have previously purchased Interior or MR (moisture resistant) plywood for construction purposes, you should now purchase plywood to comply with EN 636, Class 1.
- If you have previously specified or purchased WBP (weather and boil-proof) or Exterior quality plywood for construction purposes, you should now purchase plywood to comply with EN636, Class 3.
