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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. At Mold on Fiberboard Insulating Sheathing we discuss mold growth on or in fiberboard sheathing.

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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 (an example fiberboard product photograph is shown at left), 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 besides Homasote™, and Masonite™ 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 by (or in some cases coated 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 fiberboard 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.).

Fiberboard Roof Sheathing

Fiberboard products were also used for roof sheathing produced by several manufacturers.

Watch out: OPINION-DF: where fiberboard roof sheathing was used alone to support roof shingles or other roof coverings, and noting that fiberboard products and their performance varies by manufacturer, application, and installation details, some fiberboard products may become fragile with age, traffic, or leaks, risking roof shingle blow-off, or worker fall injuries. On a roof replacement job one of our workers [DF] stepped onto an area where the roof decking had been damaged by leaks, and broke through to the attic below.

According to Homasote[1], at least two important clarifications are in order:

Our roof application is a structural roof deck (2’ X 8’) product which in  the 46 years I’ve been associated with Homasote has never failed if installed properly. Our deck will wick out any water if installed properly.

One should not refer to fiberboards as if all fiberboards were the same. Our [Homasote®] products are much denser then the other fragile ones manufactured in the U.S. and are thus considered superior by the industry.

Homasote® roofing products include

• Firestall®
• EasyPly® Roof Deck
• Thermasote® Nailbase Roof Insulation
• N.C.F.R.® Thermasote® Nailbase Roof Insulation

When stripping existing roof shingles to perform a shingle tear-off for re roofing, Homasote® and other fiberboard roof sheathed roofs require special precautions to avoid damaging the roof sheathing during shingle tear-off. Homasote® provides the following advice: [Quoting from "Roof Shingle Tear-Off Procedure for Homasote Products" available from Homasote ].

The removal of existing shingles to re-roof Homasote roof deck or nailbase roof insulation requires a change from the conventional tear-off method used to re-roof wood surfaces.

To strip existing shingles from a Homasote roofing product, the following must be done:

1. Instead of getting under shingles with a “shoveling motion” and then scraping forward to get the nails out you must use a stripping tool or roof shovel to pry up shingles away from the deck, by pulling the nails straight out.
2. Care must be taken so that the roof shovel does not damage the surface of the deck.
   Inspect the condition of the deck as the tear-off continues. Any stubborn nails remaining after the shingles are removed should be pulled out using a crowbar or claw hammer along with a wood block as a fulcrum to prevent damage to the deck.
3. Inspect the stripped deck for any signs of deterioration or physical damage. Any damaged areas should be replaced with the same Homasote product.
4. Prepare deck for the new finish roof installation in accordance with standard roofing practice and the roofing materials manufacturer’s installation instructions. The Homasote Company requires the use of a ring-shank roofing nail for all shingle installations.

Installation instructions, general requirements and the most up-to-date information on Homasote roofing products are available from Homasote.®.

Fiberboard Sound Insulation

Fiberboard products are also used for sound insulation, such as Homasote's 440 SoundBarrier used on walls and over subflooring or in ceilings. According to Homasote this system is recognized in UL L500 Series Floor/Ceiling assemblies.

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.

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.

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.

Celotex®, Homasote®, Thermafiber®, 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.

Identifying Homasote® Brand Fiberboard

According to Homasote®,

[Homasote brand fiberboard products in] cross section would not show layers of fiber since our products, unlike other fiberboards, are not layered.

With aging our products normally have a yellowish brown tint otherwise they are gray.

In all cases, unsanded Homasote Products all have very visible patterns on the face and back side surfaces. As far as I can tell, none of the samples shown below [at Unidentified Fiberboard Products] have our mold patterns.

Each fiber is coated with a wax emulsion thus making the panel weather resistant. In a vertical application, should the panel get wet, the water will wick out the bottom as long as it’s installed properly and elevated off the bottom surface. In a horizontal application it will react like plywood and the water should not de allowed to pond on it especially after it stops raining.

Unidentified Fiberboard Products

At left is an insulating fiberboard product that is not the Homasote™ brand. Homasote Chairman and CEO Warren L. Flicker has generously added these comments that assist in distinguishing among fiberboard product brands and manufacturers: The pictures at left and below show a brown side and a black side [and show layering when broken to expose the material in cross-section]. They are not Homasote®.

Our photos (above left and right) show close ups of fiberboard insulating building sheathing board products that are not Homasote™ brand, including a torn cross section showing the layered fibrous character of this material.

Our photo (left) shows pieces of fiberboard 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. According to Homasote® this is not their product.

Where structural shear strength is needed by using the company's recommended ring-shan ked nails in a specified nailing pattern.

Identifying Celotex® Insulating Board and Fiberboard Products

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 insulating sheathing board product.

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

Mold Growth & Wood Boring Insect Susceptibility of Fiberboard 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 material.

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 fiberboard sheathing product, probably Beaver board or Upson board (in the attic of a leaky building, below right).

See Mold on Fiberboard Insulating Sheathing our full article on mold growth on or in fiberboard sheathing.

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

Questions & Answers regarding this article

Questions & answers about fiberboard building sheathing.

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SHEATHING, FIBERBOARD
SHEATHING, Gypsum board
SHEATHING Homasote & Other Board
SHEATHING, OSB
SHEATHING, Plywood
SHEATHING, FOIL FACED - VENTS

• [1] Homasote® Company, 932 Lower Ferry Road, West Trenton, NJ 08628-0240 Tel: 800-257-9491 Ext 1332, or from outside the U.S. call 609-883-3300. Website: http://www.homasote.com/ , Email: Sales@homasote.com.
• Thanks to Homasote CEO Warren Flicker for technical review and comment on this article.
• Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• [2] Celotex Corporation, headquartered in Tampa, FL, is a national manufacturer of residential and commercial building materials. www.celotex.com 800-CELOTEX
  
• [3] 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
• [4] 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
• [5] "Roof Shingle Tear-Off Procedure for Homasote Products", PDF document, Homasote Co., 932 Lower Ferry Road, West Trenton, New Jersey 08628-024, U.S.A. 800-257-9491 website: at www.homasote.com
• [6] Thermafiber, Inc., 3711 Mill Street, Wabash, IN 46992, 260-563-2111 www.thermafiber.com
• [7] 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.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

• Basement Moisture Control, U.S. Department of Energy
• Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
• Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724 ISBN-13: 978-0471331728
• Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
• Construction Drawings and Details, Rosemary Kilmer
• Crawl Space Moisture Control, U.S. Department of Energy
• Design of Wood Structures - ASD, Donald E. Breyer, Kenneth Fridley, Kelly Cobeen, David Pollock, McGraw Hill, 2003, ISBN-10: 0071379320, ISBN-13: 978-0071379328
  This book is an update of a long-established text dating from at least 1988 (DJF); Quoting:
  This book is gives a good grasp of seismic design for wood structures. Many of the examples especially near the end are good practice for the California PE Special Seismic Exam design questions. It gives a good grasp of how seismic forces move through a building and how to calculate those forces at various locations. THE CLASSIC TEXT ON WOOD DESIGN UPDATED TO INCLUDE THE LATEST CODES AND DATA. Reflects the most recent provisions of the 2003 International Building Code and 2001 National Design Specification for Wood Construction. Continuing the sterling standard set by earlier editions, this indispensable reference clearly explains the best wood design techniques for the safe handling of gravity and lateral loads. Carefully revised and updated to include the new 2003 International Building Code, ASCE 7-02 Minimum Design Loads for Buildings and Other Structures, the 2001 National Design Specification for Wood Construction, and the most recent Allowable Stress Design.
• Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
• Domestic Building Surveys, Andrew R. Williams, Kindle book, Amazon.com
• Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting:
  A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
• Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008) ISBN-10: 0471788368 ISBN-13: 978-0471788362
• Moisture Control in Buildings, U.S. Department of Energy
• Moisture Control in Walls, U.S. Department of Energy
• R-Value of Wood, U.S. Department of Energy
• "Vapor Barriers or Vapor Diffusion Retarders", U.S. DOE: how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
• ...