Celotex old insulating board (C) Daniel FriedmanFiberboard Building Wall, Ceiling & Roof Sheathing
Insulating Board Sheathing, Sound Insulation Board Product Guide

  • SHEATHING, FIBERBOARD - CONTENTS: How to recognize/identify Celotex®, Homasote®, Masonite® Nu-Wood® and other insulating fiberboard building sheathing products used as exterior wall sheathing and as interior wall & ceiling surfaces. Fiberboardf was used indoors as both a finish-surface to be painted or as a base to which plaster and then paint were applied.
  • POST a QUESTION or READ FAQs about fiberboard building sheathing: how to identify fiberboard products, fiberboard uses, fiberboard, Celotex, Homasote, Insulite & other brands, fiberboard ingredients, does fiberboard contain asbestos?
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Fiberboard insulating sheathing used on or in buildings:

Definition, ingredients, history, use, fire resistance & insulating properties of fiberboard sheathing. 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, Insulite, and Masonite insulating board sheathing products.

Here we provide fiberboard product names and we describe the components, properties, and applications of various fiberboard, hardboard, and insulating board or sound deadening board products. We also answer questions such as do Celotex or Homasote or other fiberboard and insulating board products contain asbestos? fiberboard water resistance, fiberboard recycling.

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

Fiberboard sheathing (C) Daniel Friedman

Article Series Contents

What is Fiberboard Insulating Sheathing?

Fiberboard insulating sheathing board was used and continues in use as a structural wall sheathing board 15/32-inches thick (one board was 1/2") and with R-value of about 1.5.

Shown above: fiberboard sheathing used to enclose a soffit overhang. [Click to enlarge any image]

Fiberboard insulating sheathing was and continues to be made of plant cellulose such as wood fibers, combined with a binder, a water-resistive coating or component (such as paraffin and/or asphalt), and other treatments that we detail below. Structural properties and moisture resistance were confirmed by US FPL testing. Moisture uptake did not exceed 2.2%.[15]

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 DRYWALL, PLASTER, BEAVERBOARD 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.

A History of Fiberboard Insulating Sheathing

In addition to plywood, OSB, and gypsum board, impregnated fiberboard produced in 4 ft. widths and varying lengths up to 12-feet 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).

Actually hardboard is older than that. According to the Boston Museum of Fine Arts, fiberboard was first patented in 1858 and was produced by a number of manufacturers (listed below) and made of a variety of plant fibers (including bagasse from sugar cane) or wood chips, wood byproducts, and by one company waste paper and by another company flax shives [12][15] .

Indeed it was Lyman's 1858 invention of a method for separating the fibers of wood, probably born from other work on improving the cotton gin, felting hat bodies, and making paper, that made these products possible.[13]

Fiberboard wall sheathing (an example fiberboard product photograph is shown at above 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.

A 1955 U.S. FPL report offers the early history of growth in the use of insulating fiberboard sheathing.

Insulating fiberboard sheathing is used extensively in house construction. In 1920 insulating board accounted for only about 4 percent of the sheathing used for new residential construction. In 1940 its use had risen to 20 percent and by 1950 to 30 percent.

It is more popular in certain regions of the country than others. In 1950 about 50 percent of the wall sheathing used in the Middle West [of the U.S.] was of fiberboard, while in the Pacific Northwest where lumber is more easily obtained, insulating fiberboard was used in only about 10 percent of the new houses erected. [15]

In earliest use, fiberboard sheathing material was sold as a means of insulating the home at little additional cost since it was used to replace the horizontal or diagonal tongue-and-groove board sheathing that was in wide practice up to the 1940's or 50's.

But despite early claims (later dropped) that wood fiber sheathing was a structural material, in homes where fiberboard sheathing was used, additional framing was commonly constructed at the building corners as diagonal bracing to stiffen the building walls.

Modern product literature for fiberboard insulation[2] and standards for products such SturdyBrace® Structural Fiberboard Sheathing [14] make clear that the product is produced and used as structural sheathing. Quoting:

STURDYBRACE® improves the structural integrity of homes and light commercial buildings and eliminates the need for corner bracing. The product meets codes for wind shear and seismic conditions [2]

Synonyms for Fiberboard Insulating Sheathing

Synonyms for fiberboard include: brown board or brownoard, insulating board, Celotex, Homasote, Insulite, "fibre-board (Br.); fibreboard (Br.); carton-fibre (Fr.); carton fort (Fr.); aglomerado de madeira (Port.); particle board; composition board; wallboard; hardboard; fiber board; high-density fiberboard (HDF); medium-density fiberboard (MDF); low-density fiberboard (LDF)[11]

Additional fiberboard insulating sheathing product names appear throughout this article.

Fiberboard Manufacturers & Product Brand Names

Celotex old insulating board (C) Daniel Friedman

Above: Celotex fiberboard marking identification. [Click to enlarge any image]

Note: our separate article SHEATHING, FIBERBOARD IDENTIFICATION includes identifying markings and photos of many of these products.

Nu-Wood Interiors catalog pages (C) InspectApedia

Excerpt from documents at the Minnesota Historical Society's Manuscripts Collection:

The Wood Conversion Company was incorporated in 1921 in Delaware by eleven stockholding companies, including the Weyerhaeuser firms. The headquarters was located in Cloquet, Minnesota.

The headquarters later moved to Saint Paul, although the company's plant operations remained in Cloquet. On August 1, 1967, an amended certificate of incorporation filed in Delaware changed the name of the corporation to Conwed Corporation. In 1985 the stock of Conwed Corporation was sold to Cardiff Equities Corporation, a subsidiary of the Leucadia Corporation of New York.

Also see

"Conwed Corporation, An Inventory of Its Records at the Minnesota Historical Society Manuscripts Collection", Minnesota Historical Society, retrieved 2015/12/04, original source:

Wood Conversion Company, "NU-WOOD INTERIORS FOR EVERY WALL AND CEILING", [PDF] Wood Conversion Company, St. Paul Minnesota, (u1936), retrieved 2015/12/04, original source: Nu-woodInteriorsForEveryWallAndCeiling/ Nu-woodInteriorsForEveryWallAndCeiling_djvu.txt, This companyu was a producer of Balsam Wool & Nu-Wood, Nu-Wood Tile, Plank and Wainscot and similar products.

See SHEATHING, FIBERBOARD ASBESTOS CONTENT for a discussion of asbestos and Nu-Wood / Conwed products or processing plant asbestos hazards

In the article below we provide additional details about fiberboard product names and we describe the components, properties, and applications of various fiberboard, hardboard, and insulating board or sound deadening board products. These product names include

What is Fiberboard Insulating Sheathing Made Of?

This discussion has moved to a separate article now found at FIBERBOARD SHEATHING INGREDIENTS

Fire Ratings & Fire Resistance of Fiberboard Sheathing


Importance of Protecting Fiberboard Insulating Sheathing from Water

This discussion is moved to PROTECT FIBERBOARD from WATER

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. Any significant or chronic water leakage in a roof whose shingles are supported by fiberboard insulating sheathing risks a roof surface collapse.

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

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.

Identify Fiberboard & Insulating Sheathing Board & Plasterboard Products


Fiberboard Sheathing Asbestos, Off-gassing, VOCs, Health & Environmental Questions

Celotex insulating lumber

ASBESTOS: Is there Asbestos Content in Insulating Board Products such as Celotex, Homasote, Insulite or Nu-Wood?

Asbestos is not an "official" ingredient in fiberboard insulating sheathing. However there are possibilities of cross-contamination of such products by asbestos as asbestos was processed at some of the same fabrication facilities that also made wood or vegetable fiber board products.



OFF-GASSING: Question: off-gassing hazards from low density fiberboard roof sheathing vs MDF Sheathing

5/9/2014 Anonymous said:

Are there any cases of individuals suffering health issues from exposure to a fiberboard roof? I"m thinking of off gassing due to excessive exterior heat conditions.


Offgassing from fibergoard roof? Most likely you're asking about fiberboard roof sheathing, right? I'm doubtful you'll be able measure significant offgassing from low density roof sheathing products in service such as soft density or low density fiberboard.

However more recently there are indeed MDF products sold for use as structural panels including roof sheathing. Details are at Definition & Characteristics of MDF Medium-Density Fiberboard

The article above on this page describes low density fiberboard products and explains that describes how that sheathing material is produced describes wood products and waxes. So to start we'll want to get clear what sort of roof sheathing you are actually describing.

Research on VOC Emissions & Building Materials

Here are some helpful citations that describe the ingredients, manufacturing process, and research of several types fiberboard products. You will find citations (including some I give below) of outgassing of MDF fiberboard products used in other applications (not the soft "Homasote®" type roof sheathing board):

Disposal of Fiberboard Demolition Debris:

Reader Question: can we dispose of fiberboard by using it as mulch?

Is Celotex recyclable? We just removed some and I wondered if it could just be broken up on the ground like mulch or does it have chemicals in it. - Karen Bradshaw 7/25/11

Reply: fiberboard sheathing or insulating boards are not recommended as yard mulch

Karen the recycle-ability of fiberboard sheathing products like Celotex or Homasote is an interesting one. These products that are made principally of wood fibers or other plant fibers and a binder and are usually disposed of as construction debris. The properties of insulating fiberboard sheathing were thoroughly described by the U.S. Forest Products Laboratory in a 1955 report[15] as well as in original and current manufacturer's product literature and MSDS sheets.

But watch out: trying to break up any fiberboard product into small mulch like fragments risks creating an irritating or problematic dust hazard for eyes and respiration.

I'm unsure how well the binder or coating chemicals are bonded to the material (some products used paraffin), but I wouldn't use this product for mulch in any case. Some newer insulating boards may contain plastics and some older ones appear to contain bituminous coatings or binders.

You will find that the treatments used to make these insulating boards moisture resistant and to impart stiffness also mean that they will not break down or bio-degrade as a yard mulch.

MSDS data for fiberboard insulating sheathing products

Fiberboard exterior or interior sheathing sheets are benign products for the most part, though wood dust particles from any wood material can be a potential hazard.


Mold Growth & Wood Boring Insect Susceptibility of Fiberboard Building Insulating Sheathing Products


Article Series Contents


Continue reading at SHEATHING FIBERBOARD CONSTRUCTION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



Or see INSULATION IDENTIFICATION GUIDE - home for identification of various insulating board products

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FIBERBOARD SHEATHING at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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