OSB Use Classes – Additional Guidance

Specific information on the application of Use Classes to OSB has not been included in the updated EN 335:2013. This guidance was originally given in the now withdrawn EN 335-3:1995 for OSB. As this is important information, APA are providing it below.

OSB Use Class definitions

 Use Class
                                               Definitions

 

1

 In this environment, OSB will have a moisture content no higher than that which would result from exposure to an air temperature of 20°C and a relative humidity of 65% for practically the whole of its service life.  They may be regarded as being dry with little risk of attack by surface moulds, staining moulds or wood-destroying fungi.  There is no risk of attack by wood-destroying insects except termites.

 

2

 In this environment, the moisture content of an OSB panel, either in the whole or only in part, can occasionally attain or exceed that which would result from exposure to an air temperature of 20°C and a relative humidity of 90%. The moisture content can occasionally increase to a level which can allow the growth of wood-destroying fungi.  Disfigurement can also occur as a result of the growth of surface moulds and staining fungi. Risk of insect attack is similar to that for Use Class 1.

 

3

 In this environment, OSB can frequently have a moisture content above 20% and thus will often be liable to attack by wood-destroying fungi. Disfigurement can also occur as a result of the growth of surface moulds and staining fungi. Risk of insect attack is similar to that of Use Class 1.

 

4

 In this environment OSB has a moisture content permanently above 20% and is, therefore, liable to attack by wood-destroying fungi. The risk of insect attack to that portion of the panel situated above ground or water is similar to that for Use Class 1. Termites can be an additional problem in certain geographical regions.

 

5

 In this environment, OSB panels are permanently above 20% moisture content and are wholly or partially submerged in salt water. Attack by invertebrate marine organisms is the principal problem. Limnoria spp. and Teredo spp. are problematic in warm waters. Also, the OSB is liable to attack by wood destroying fungi. Risk of insect attack to that portion of the OSB which is above the water level is similar to that for Use Class 1. Termites can be an additional problem in certain geographical areas.