Conceptual Reference Database for Building Envelope Research Prev
Related Concept
  • Vapor permeability of OSB is low: OSB - Oriented strandboard
  • HAM: material properties

  • Related References


    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).

    Other mechanical properties (such as springback, nail and screw holding capacity, quality of surface, and machining behavior) are suitable for exterior and roof sheathing under normal conditions. The thermal property of OSB is similar to that of plywood.

    There are more differences in hygroscopic properties between OSB and plywood and fiberboard, especially the vapor permeability and moisture diffussivity. As shown in Table below, the value of vapor permeability of a OSB board is one magnitude less than the wood and much less than that of the plywood panels. Using of OSB as wall sheathing is essentially adding a vapor barrier at the outside layer of the envelope in addition to the inside barrier.

      dry density[kg/m]

    thermal conductivity [W/(m.K)]

    sorption isotherm


    at 50% RH]

    vapor permeance[kg/(m2 Pa) 10‑10 at 80% RH]

    moisture diffusivity [m2/s x10-10 at 30% moisture content]

    air permeability [kg/(m.s.Pa)x10‑9

    at 50 Pa]






















    [By J. Rao, 1999]

    Related Articles:

    CRDBER, at CBS, BCEE, ENCS, Concordia,