Durable, weather-resistant substrate for many different exterior claddings


1. Brick Underlayment     2. Exterior Ceiling
Fiberglass-Faced Gypsum Sheathing helps protect a structure against air, water and noise infiltration.
Physical Description
Exterior Gypsum Sheathing is a specialized performance panel consisting of a noncombustible, moisture-resistant core encased in fiberglass facers on both front and back surfaces and long edges. Previously produced with treated paper facers, the product is now overwhelmingly manufactured with fiberglass mat surfaces especially when made for commercial construction. Gypsum Sheathing is typically available with square edges in 1/2” (12.7 mm) and 5/8” (15.9 mm) thicknesses, a 48” (1220 mm) width and lengths from 8’ (2440 mm) to 16’ (4880 mm). In addition, 1/2” (12.7 mm) panels normally feature a regular core and 5/8” (15.9 mm) panels a Type X core for use in fire-resistive assemblies. The applicable product manufacturing standard is ASTM C1177. Refer to GA-254 Fire-Resistant Gypsum Sheathing.

Advantages and Benefits
Fiberglass-Faced Gypsum Sheathing is a product well-proven in commercial construction applications since the mid 80’s. It provides a list of valuable benefits when specified as a component material in a project’s exterior envelope and refinements continue to enhance its cost-efficiency and performance.o Weather Protection – Gypsum Sheathing’s moisture-resistant core and fiberglass facers provide a structure extended protection against water and air infiltration. This characteristic also helps protect the product itself when exposed to weather during a project’s construction process.o Mold Resistance – Gypsum Sheathing does not contribute to the growth of mold or mildew because of its glass mat facers and anti-microbial core treatment. In addition, its vapor permeability helps prevent trapped moisture in the wall cavity.o Fire Resistance – Thanks to its noncombustible gypsum core and glass-mat surfaces, tested values for flame spread and smoke generation are very low for exterior Gypsum Sheathing. Produced with a Type X core, 5/8” (15.9 mm) Gypsum Sheathing is UL-classified for use in fire-rated assemblies. Refer to GA-600 Fire Resistance and Sound Control Design Manual.

o Exterior Systems Compatibility – Not only is Gypsum Sheathing a compatible underlayment for many different exterior finish materials including wood, masonry, metal, vinyl and stucco systems, but it is also a widely accepted application surface for weather-resistive barriers and coatings.

o Construction Efficiency – Versatile, practical and easy to apply, exterior Gypsum Sheathing can be used in multiple applications to streamline material procurement, reduce material and labor costs and tighten the construction schedule for exterior walls.

o Noise Attenuation – Gypsum Sheathing can be a component material in a number of sound control assemblies developed to dissipate the energy of sound vibrations within a structure. Expressed in terms of ranged Sound Transmission Class (STC) values, tested assemblies provide a comparative reference to help architects design structures that meet specific acoustical performance targets. more

To fully meet the design objectives required for a structure’s exterior wall and ceiling surfaces, a number of important limitations should be followed to maximize the performance of fiberglass-faced Gypsum Sheathing. These recommendations are intended to provide general information only about considerations that are common in this category of special performance gypsum products:

o Gypsum Sheathing is not designed to be a nail base for exterior cladding – fasteners must be attached to furring strips or framing
o maximum framing spacing should be no greater than 24” (610 mm) o.c.
o do not apply panels below grade
o do not laminate Gypsum Sheathing directly to masonry surfaces – use furring strips or framing
o not intended for use as an interior or exterior tile backer
o not designed to replace structurally engineered sheathing in shear walls

Refer to the document GA-253 Application of Gypsum Sheathing for specific guidelines related to the handling and application of exterior Gypsum Sheathing.

Products vary by brand. For more specific limitations related to the gypsum panel you are considering, consult with the product’s manufacturer.

Frequently Asked Questions
Below are answers to typical questions our technical experts address on a routine basis. These answers may provide additional information you are seeking as well. To submit an inquiry of your own, click here.

1. How long can exterior Gypsum Sheathing be exposed to the elements?

Exterior Gypsum Sheathing should never be stored outside while awaiting application. Details on the safe handling and storage of all gypsum panel products is available in the free technical document GA-801 Handling and Storage of Gypsum Panel Products.
Prevailing weather conditions will dictate how long exterior Gypsum Sheathing can be exposed to the elements after installation. Weather exposure of up to one month should not affect performance. Contact the manufacturer if you have questions related to a specific job or set of weather-related conditions as extended exposure recommendations vary by product brand.

2. How is Gypsum Sheathing cut and installed?

Detailed instructions for the application of Gypsum Sheathing are provided in the Gypsum Association’s free technical document GA-253 Application of Gypsum Sheathing. Gypsum Sheathing is easily cut to size with a utility knife. No special tools are required. Joints between sheathing panels should be staggered. Sheathing is nailed, screwed, or stapled directly into wood or steel framing in such a manner that the fastener sits tightly against the sheathing without breaking the glass matt surface. GA-253 provides essential information on the type and size of fasteners, the appropriate water-resistive barriers for application to installed sheathing, as well as details on cutting holes for pipes and other utilities and the application of flexible water-resistant sealant to those openings.

3. Does Gypsum Sheathing offer any advantages to a builder of single-family homes?

While more frequently used in multifamily residential construction, exterior Gypsum Sheathing provides the same advantages to builders of single-family homes. When compared to wood sheathing alternatives, exterior Gypsum Sheathing has greater fire resistance and mold and moisture resistance. Because it contains no wood, glass mat Gypsum Sheathing is not susceptible to attack by wood boring insects. Easier to install and repair than wood products, Gypsum Sheathing is not a nail base for fasteners but is an excellent substrate for stucco, EIFS, stone and brick, as well as wood and composite siding products and more. While Gypsum Sheathing does not provide racking quality, this limitation is easily overcome through the addition of bracing.