Exterior Gypsum Sheathing: Multi-Family Homes

Physical Description
Exterior Gypsum Sheathing is a specialized performance panel consisting of a noncombustible, moisture-resistant core wrapped in glass mat facers on both the front and back surfaces and long edges. Exterior Gypsum Sheathing is manufactured with square edges in both 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). Typically, 1/2” (12.7 mm) panels feature a regular core and 5/8” (15.9 mm) panels are produced with 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
Glass Mat Gypsum Sheathing has a well-proven record of cost-efficient performance in multi-family construction since the mid 80’s. It provides multiple practical benefits when specified as a key component in a project’s exterior envelope.o Weather Protection – Gypsum Sheathing is manufactured with an enhanced moisture-resistant core and glass mat facers to provide a structure extended protection against water and air infiltration from the external environment. This characteristic also helps protect the product itself when exposed to weather during a project’s construction process.o Mold Resistance – Gypsum Sheathing’s naturally mold-resistant glass mat facers and anti-microbial core treatment help prevent costly and potentially damaging mold growth and decay. Products in this category score extremely well in laboratory mold tests in accordance to ASTM D3273. In addition, its vapor permeability allows exterior walls to release moisture originating inside the structure before it becomes a bigger issue.

o Fire Resistance – Especially important in multi-family design solutions, 5/8” (15.9 mm) Gypsum Sheathing is produced with a Type X core and is UL-classified for use in fire-rated assemblies. Its noncombustible gypsum core and glass-mat facers not only provide tested resistance to burning, but they also produce extremely low flame spread and smoke-generated values as well. Refer to GA-600 Fire Resistance and Sound Control Design Manual.

o Exterior Systems Compatibility – Gypsum Sheathing is a compatible underlayment for a wide range of different exterior finish materials including wood, brick, stone, metal and vinyl, as well as popular EIFS and stucco systems. 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 installed quickly and without specialized tools or techniques. Its versatility for application as a substrate for multiple cladding options, helps streamline procurement, lower material 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 multi-family structure. These tested assemblies provide a proactive strategy to minimize the noise entering a structure from outside as well as to inhibit the noises transmitted from one leased space to another. more

Limitations
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 Glass Mat 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 mat 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.