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Fiberboard Building Sheathing & Insulating Board Sheating Product Guide InspectAPedia®  -     How to recognize Celotex®, Homasote®, Masonite® and other insulating board building sheathing products Characteristics and composition of wood and paper product insulating sheathing panels used on walls, roofs, and on building foundations Building component age: construction materials, methods, including hardware, saw cuts, and other details can help determine when a building was constructed or when it was modified.

This article describes and provides photographs that aid in identifying various insulating board sheathing materials used on building walls and roofs, such as Homasote, Celotex, and Masonite insulating board sheathing products. Readers should also see Sheathing, Gypsum board, and Sheathing, OSB as well as Sheathing, Plywood for a discussion of these common building roof and wall sheathing products. At Plaster & Beaverboard & Drywall we discuss other interior sheathing boards that were used on interior walls and ceilings. At SIDING HARDBOARD we discuss hardboard exterior building siding such as sold under the Abatibi and Boise Cascade brands.

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Fiberboard Building Sheathing: Black board, grayboard, buffaloboard exterior sheathing

In addition to plywood, OSB, and gypsum board, impregnated fiberboard has been used as exterior building insulating sheathing in North America since at least 1909 (see our discussion of Homasote, below and see Masonite™ and other hardboard Sheet and Siding Building Materials).

Fiberboard wall sheathing, when intended for use on a building exterior is installed by nailing directly to the wall studs, most often with let-in diagonal bracing or plywood panel bracing at the building corners to assure building rigidity.

There both non-structural and structural fiberboard panels that did not require this additional bracing have been produced. Some fiberboard sheathing products can claim adequate structural shear strength, particularly if the proper nails and nail pattern are used.

Other contemporary producers of fiberboard building sheathing include International Bildrite (Bildrite structural), Georgia Pacific (Stedi-R & Stedi-R-structural), Knight Celotex (Celotex premium insulating), and Temple Inland (Temple fiber brace).

Fiberboard sheathing, also called black board, gray board, or buffalo board sheathing in some areas, is a fibrous material impregnated with a stabilizer and water repellant - asphalt on early versions of this material that we have found. While it's not easy to find and identify this material on a building wall unless indoor or outdoor demolition is being performed, you can spot the product in building attics on the gable-end walls.

The R-value of fibergoard sheathing is higher than plywood, gypsum board, etc, and is rated at about R 2.4 per inch (or about R 1.2 in more typical half-inch thickness with which it is applied. The board also reduces sound transmission into buildings. r framing in North America continued until about 1920. (CF Reference due: Age of Barns, op.cit.)

Guide for Identifying Photographs of Homasote®, Celotex®, & Similar Fiberboard & Insulating Sheathing Board Products

Insulating building sheathing made by Homasote® is produced by the Homasote Company, a manufacturer in the U.S. in New Jersey, and similar fiber sheathing products have been used both as a sound barrier and for exterior sheathing on buildings. Insulating board sheathing has been widely used on building exterior walls, under roofs, and against masonry foundations in finished basements. Originally, Homasote produced sanded "agasote" sheets used in the roofs of passenger railroad cars, moving, in 1915, to automobile roofs, and in 1916 to construction products. Homasote was widely used for military barracks in both WWI and WWII and is still promoted for sound resistant sheathing and other applications. Homasote and similar insulating building sheathing board products are still sold as a lower cost alternative to plywood or OSB for building sheathing. The product is used as structural paneling, insulation, concrete pouring forms, and expansion joints.

Our photos (above left and right) show closeups of Homasote-type insulating buildnig sheathing board products, including a torn cross section showing the layered fibrous character of this material.

Our photo (left) shows pieces of Homasote-type roof insulating fiberboard removed from a building by reader/contributor Doug Leen. The varying colors of the two sides of the material are visible - the darker side of this insulating board may have been that exposed to light and air during its life in the building. The material looks like a Celotex product. According to Thermafiber it is not their product.

Where structural shear strength is needed by using the company's recommended ring-shanked nails in a specified nailing pattern. Homasote Co., the oldest manufacturer of building products from recycled materials in the United States, was founded by Eugenius Harvey Outerbridge as Agasote Millboard Company, and has been producing this material since 1909. In 1936 the company changed its name to its best known product, Homasote.

Our photographs below show Celotex® insulating board with an older Celotex fiberboard building sheathing board at left and a more recent Celotex insulating board product shown at below-right. Also see this closeup of an older Celotex inslulating sheathing board product.

Also see Fiberboard insulating sheathing or board sheathing products and see Masonite® hardboard siding products.

Mold Growth & Wood Boring Insect Susceptability of Fibergboard Building Insulating Sheathing Products

We do not usually find mold growth on fiberboard building insulating sheathing nor insect damage to this material. Possibly the resin binder and coating is unattractive to insects and the moisture resistance of some coatings also reduce the ease of mold growth on this materia.

However in sufficiently challenging conditions such as very wet conditions or prolonged exposure to water and moisture or insects, we have found both extensive mold growth on Homasote type insulating board (photo, below left, in a wet basement against a masonry wall) and evidence of insect damage to an interior wall fibergoard sheathing product, probably Beaver board or Upson board (in the attic of a leaky building, below right). At Plaster & Beaverboard & Drywall we provide the history of Beaver board and Upson board, and we discuss other non-structural interior sheathing boards that were used on building interior walls and ceilings.

Masonite™ and other hardboard Sheet and Siding Building Materials

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• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Celotex Corporation, headquartered in Tampa, FL, is a national manufacturer of residential and commercial building materials. www.celotex.com 800-CELOTEX
  
• Douglas Leen, Petersburg AK 99833, contributed the photograph of insulating board scraps from roof insulation removed from a building. Dr. Leen provides such a wide range of services, collectables, and historical information about the Northwest that a succinct description is difficult: flying dentist goes anywhere, antique forestry posters, historic campers, the tugboat Katahdin, in Alaska, Washington, and Wyoming. Mr. Leen can be contacted at mail@dougleen.com or at 907-518-0335
• America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
• American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, apawood.org 253-620-7400 APAWood.org
• Georgia Pacific: information about DensGlas gypsum board building sheathing can be found at the company's website at gp.com/build/product.aspx?pid=4674
• Homasote Co., 932 Lower Ferry Road, West Trenton, New Jersey 08628-024, U.S.A. 800-257-9491 homasote.com
• "Hurricane Damage to Residential Structures: Risk and Mitigation", Jon K. Ayscue, The Johns Hopkins University, Baltimore, Maryland, published by the Natural Hazards Research and Applications Information Center, Institute of Behavioral Science, University of Colorado, November 1996. Abstract:
  "Property damage and loss from hurricanes have increased with population growth in coastal areas, and climatic factors point to more frequent and intense hurricanes in the future. This paper describes potential hurricane hazards from wind and water. Damage to residential structures from three recent intense hurricanes - Hugo, Andrew, and Iniki - shows that wind is responsible for greater property loss than water. The current state-of-the-art building technology is sufficient to reduce damage from hurricanes when properly applied, and this paper discusses those building techniques that can mitigate hurricane damage and recommends measures for mitigating future hurricane damage to homes." - online at www.colorado.edu/hazards/publications/wp/wp94/wp94.html
• Thermafiber, Inc., 3711 Mill Street, Wabash, IN 46992, 260-563-2111 www.thermafiber.com
• Weaver: Beaver Board and Upson Board: Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver, APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.

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