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External Sheathing: A Guide

External Sheathing: A Guide

In order to protect the walls of a building from the elements, it is often necessary to use an exterior sheathing material. There are two types of sheathing options available – structural and non-structural. Where structural sheathing offers additional strength to the frame of the house, non-structural sheathing adds insulation value to the building thereby increasing its energy efficiency as well as protecting the structure from wind and water.

There are many external sheathing options available, each of which have slight differences in integrity as well as application areas.


Gypsum-Based Exterior Sheathing

Non-structural exterior sheathings that fall under this category are specialized performance panel made of a fire-proof, moisture-resistant core sandwiched between fiberglass faces. Often, the gypsum bases is mixed with a high concentration of fiberglass throughout the board. Gypsum exterior sheathing is available with square edges in 1/2” and 5/8” thicknesses and usually available in standard 4’x8’ size. In addition, the 1/2” panels feature a regular core and 5/8” panels a Type X core for use in fire-resistive assemblies.

Products like DensGlass® and DensDeck® are used together for vertical exterior sheathing and parapet sheathing respectively. The CertainTeed brand of GlassRoc® serves the same purpose and provides valuable benefits in terms of water and air resistance, which also helps protect the building during construction. Thanks to the fire-resistant gypsum core and glass-mat surface, these exterior sheathing generate very low smoke and flame spread value during testing. These products are suitable for extra-wide overhangs like storefronts, awnings, parapet backing, and breezeways.


Fire Treated Plywood

Fire treated plywood sheathing is necessary in many commercial construction applications in order to comply with safety codes. Products like Dricon®, Pyro-Guard® are made from sheets of wood that are cross-laminated to give the boards strength and stiffness. Plywood is much lighter than OSB sheathing and its moisture resistance and drying rates make it suitable for roof sheathing, partition walls, storefronts and roof construction in shopping centers.


Extruded Polystyrene/ Rigid Foam Board

When extra insulation is needed on the exterior of the home, use rigid foam board. Usually made from polystyrene or polyisocyanurate, this insulation material eliminates the need for a thermal bridge between the studs and wood sheathing on the exterior of the building. When Owens Corning Foamular® is combined with wood panel, it provides better thermal protection thereby saving energy needed to cool the building.



In summary, picking the perfect non-structural sheathing material for a building, and an associated house wrap, will depend on a variety of factors ranging from humidity levels, structural safety requirement, temperature fluctuations, fire hazards, wind speed and client budget.