OSB- hygrothermal properties as compared to other sheathing panels

OSB Properties

The properties of the boards affect the suitability, and influence the design and construction methods. The hygrothermal properties in particular will strongly influence the moisture transport and accumulation in the envelope. Their non-uniform property across the depth of the panels may also affect the modeling of the building envelope in theoretical and simulation work.

The destruction of the natural structure of wood by transformation to flakes, changes its anisotropy with regard to properties. The transformation in OSB is more drastic than in plywood, and many variables (particle morphology, arrangement in the board, method of board production, thickness, wood species, type and amount of adhesive, additives, etc.) contribute to the production of boards with different properties [2]. Table 1 lists selected properties of OSB in comparison to traditional sheathing boards.

The board density of OSB is basically affected by the density of wood, and has three ranges: low density (0.25-0.40 g/cm³), medium density (0.4-0.8g/cm³), and high density (0.8-1.2 g/cm³). Across the thickness of the board, the density is normally not uniform, it is denser near the surface and less dense in the center part. The variations constitute the so-called "density profile". Since the density affects the moisture transport, this variation will affect how the sheathing is modeled. For panels of uniform density (such as fiberboard), one node (or layer) can be used in the theoretical modeling. The OSB will need multiple nodes or layers for adequate representation.

Under the influence of moisture changes, flat-pressed boards exhibit a very low dimensional change (low shrinkage and swelling) in length and width. The change of thickness is, however, more pronounced (e.g. change in moisture content from 6 to18%

leads to a 4-9% change in thickness).