Higher durability and moisture resistance are the most important advantages of OSB 3 compared to OSB 2.
As from the mechanical properties point of view (MOR, MOE, internal bond) there is no difference between OSB 2 and OSB 3, it is the swelling rate that makes the difference between the panels and limits the domain of use for each type of board:
- Internal use in dry conditions (RH ≤ 65%) for OSB 2 → service class 1
- Internal or protected external use in dry and humid conditions (65% < RH ≤ 85%) for OSB 3 → service class 1 & 2
According to the harmonized European design standard for timber structures EN 1995-1-1 (Eurocode 5) and to EN 335 (wood protection), the outside sheathing of external building components like roof and external walls is classified as usage class 2, requiring materials classified as service class 2, that is OSB 3 or OSB 4.
From this point of view, OSB 2 can only be used for internal structural floors and partition walls or for non-ventilated roofs, where the insulation is installed above the roof sheathing.
Due to its reduced swelling rate (≤15%), OSB 3 swells, shrinks and expands less than OSB 2 (≤20%), which means reduced stress-strain of the fasteners due to change in panel thickness, which further implies a reduced risk of squeaking.
Other advantages: better sound insulation and better reaction to fire of OSB 3 and OSB 4 TOP (class D-s2, do) compared to OSB 2 (reaction to fire class E) for thickness range 9-12mm, due to slightly higher density (≥ 600 kg/m3 versus ≥ 580 kg/m3).