Fiberboard sheathing (C) Daniel FriedmanAsbestos Content in Fiberboard Building Sheathing & Insulating Board?

  • SHEATHING, FIBERBOARD ASBESTOS CONTENT - CONTENTS: does fiberboard sheathing or insulating board contain asbestos? history, research citations, answers
  • 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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Does or did Celotex® or Homasote® or other fiberboard and insulating board products contain asbestos? This article addresses worries about asbestos in fiberboard insulating sheathing - a question that comes up during building demolition and renovation. The short answer is "no" but the history is interesting. We include research citations and testing lab referrals for concerned readers.

This article series describes and provides photographs that aid in identifying various insulating board & fiberboard 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 about fiberboard water resistance, fiberboard recycling.

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Is there Asbestos Content in Insulating Board Products such as Beaverboard, Celotex, Homasote, Insulite?

Question: What is Celotex Insulating Lumber? Do insulating board products contain asbestos?

Celotex insulating lumber I have a home built in 1940 that used a brown fiber board called "Celotex Insulating Lumber" looks like is was designed to be used as sheathing and lath. Made in either Chicago on Louisiana. Anyone familiar with this? Or know if it contained asbestos? - Dan Theisen 1/30/12

6/25/2014 Sara said:

Does Beaver Board contan asbestos? I am cleaning out my grandmothers home and her basement has a beaverboad ceiling. The home is approximatly 65 years old but not sure how long the tiles have been in the basement


Dan, Celotex, a Chicago company, has been a producer of a wide variety of insulating sheathing boards for a long time and the company continues to produce modern insulating board products as well.

Celotex Insulating Lumber was introduced by the Celotex corporation in 1922, making it

"... possible for the first time to build a completely insulated house practically without extra cost". [8]

Our illustration (left) shows Celotex insulating lumber on the exterior of a Lebanon PA home.


No, beaverboard is a wood fiber product not an asbestos-product.

There was some question, not substantiated by any research I could find, that because some wood fiber board products may have been made at the same site where asbestos-containing materials had been used, that there may have been some cross contamination; that theory has not been supported.

Reader Question: Could my fiberboard sheathed house contain asbestos?

(Dec 15, 2012) Lisa said:

i live in a BISF house the interior walls are some kind of board they look like fibre board and are a light brown some are more grey..could they contain asbestos?


Fiberboard sheathing is a wood product.

Checks & MSDS Citations for Asbestos Content in Fiberboard Insulation

A review of the patents and product description for Celotex insulating lumber products shows that asbestos was not among the product's ingredients.

In "Insulite Co. vs. Reserve Supply Co", a 1932 lawsuit, relevant patents and ingredients are described, including a composition of plaster of paris, cement, or other like substance, combined with hair, wood fiber, sawdust, wool, wood shavings, excelsior, straw, or similar substances. (Asbestos was not cited in the product description. )[11]

In sum these are benign products for the most part, though wood dust particles from any wood material can be a potential hazard. For the specifics of your fiberboard siding you'll want to consult the MSDS of the particular product. For example:

  • Homasote 440 - quoting: Cellulose based material containing 1 to 2% paraffin wax, CAS 8002-74-2, and less than 0.1% copper base pesticide, CAS 39290-85-2. The product contains no known hazardous or carcinogenic components.
  • Knight-Celotex Fiberboard™ MSDS (Marrero Plant), MSDS No. 00040-85F, 4/19/2002, trade name Premium Fiberboard Insulating Sheathing, Manufactured Home USB, Coated 1 & 6 Sided, lists the following ingredients: Cellulose (<= 96%), Starch (<= 10%), Paraffin Wax (<= 2%), Carbon Black (<= 0.5%), Clay (<= 2%), and Lamination Adhesive (<= 3.5%). Original source:
  • StructoDek® high density roof insulation, laminated board & coated 1 & 6-sided, MSDS: 001-86F, 4/12/2005, Knight-Celotex LLC, Northfield IL Tel: 800-596-9699 lists these ingredients: Cellulose (<95%), Starch (<9%), clay (1%), Carbon Black (1%), Wax (1%), Laminating Adhesive (< 3.5%). Original source:
  • Sturdy-Brace High Density Fiberboard, produced by Blue Ridge™ Fiberboard - MSDS: "Hazardous Components": Wood Fiber*. [In other words, Asbestos is not present].

Watch out: * *: Wood dust is listed by the IARC as a human carcinogen (Group 1). Structodek High Density Fiberboard Roof Insulation is defined by OSHA (29 CFR Part 1910) as an "Article". A manufactured item which is formed to a specific shape or design during manufacture which does not release or otherwise result in exposure to a hazardous chemical under normal conditions of use.

In other words, the dose makes the poison for all substances.

Really?: we have read a few accounts indicating that while asbestos was not an ingredient in fiberboard insulating sheet products, some of these products may have been manufactured at or near facilities previously used to process asbestos materials. The question of cross-contamination arose but I have not yet found a report of actual asbestos contamination in fiberboard from that source (nor others).

Reader Question: does the brown insulating board found under bowling alley lane material contain asbestos?

Fiberboard insulation used under bowling alley lane (C) InspectAPedia - ACI am writing to you because I found your website after realizing I may have been handling asbestos-containing materials for the past year or so without knowing.

I don't know how it didn't occur to me sooner, but now I'm really scared and don't know where to turn for help.

I'm a teacher in NYC and, unrelated to my teaching, about a year ago I started working with old bowling lane flooring.

On the underside of bowling lane floors there is a fiberboard type material I believed was used for sound dampening.

I've handled and ripped off this material so many times without once thinking what it was- I think I was told it was Homasote and harmless.

Since many of these bowling lanes were installed many years ago, it worried me even more. Now I'm not so sure what it is and scared at the thought of what it could be.

I've spent the last few hours panicked at the computer searching for information, trying not to show my wife how scared I am.

If there is any way you could call me or share any information, I would be so grateful.

Bowling alley lane fiberboard insulation (C) InspectApedia ACYour website seems like the work of a very knowledgeable expert in this area so I'm turning to you for some advice. Attached below is a photo of some of the material- it is the black strips of material stapled to the black underside of the wooden board on the left.

Again, thank you in advance for any information you can offer. Feel free to call any time of day or night.

Thank you for taking the time to speak with me yesterday. I really appreciate your advice and insight into my situation. I attached a link below to a bunch of photos of this material that was attached to the back of three different pieces of the bowling lane.

There are just strips of this material attached with staples to the underside every few feet of the bowling lane. Some is black on the outside, some is white, and some is just like a brown cardboard color-- it all looks fairly similar on the inside.

If you can let me know what you think ASAP, that would be great- I know you told me not to be, but I am really worried about all this- I've been a mess all week at school.

Also, if you have those names or contact info for anyone who might be willing to test this material for me, that would also be incredibly helpful. I can't thank you enough for your help with this- feel free to call or email me back with any information. - A.S. 11/5/2013

Reply: The material looks like and probably is a wood fiber insulating board - not asbestos-containing. But protect yourself from demolition dust.

Fiberboard insulation fragments used under bowling alley lanes (C) InspectApediaThe material I can see in your online photos is almost certainly wood fiber based Homasote type insulating board. That is not an asbestos product. You can see more examples of this product at SHEATHING, FIBERBOARD

If nevertheless you want to have as sample of the material tested for asbestos content, the cost is usually minor - about $50. U.S. You can use any certified asbestos testing laboratory - and can find one via help given at ASBESTOS TESTING LAB LIST.

As we discussed by telephone, you should, however protect yourself from breathing dust during any demolition project.

While the material you are working with was sandwiched between other building materials: bowling alley lane surfacing and the subflooring atop the floor structure - a location where it was rather protected unless the building flooded. In that location I speculate the material would be less likely to be contaminated by other exposures.

Nevertheless, breathing high levels fine dust particles that can be released into the air by the disassembly or demolishing of building is a health risk. Ultra fine particles, down in the 1u range are probably low in dust from fiberboard sheathing, but of course I don't know what else is in the environment where you are working.

To be ultra safe while working you'd wear a HEPA-rated dust mask. At a very minimum I recommend you wear a paper N-95 dust mask as well as other appropriate protection (eyes, hands) when disassembling and demolishing these materials.

If you decide to have a section of the material tested for asbestos, I would choose a piece of the insulating board that has that white skin or coating - to check that those products were not made with a facing of asbestos paper.

The history of fiberboard insulating products is interesting in that while the product itself is not an asbestos-based material, there were some questions of cross contamination with asbestos because of the manufacturing location of some brands. However to date, except for Kollman (1975) I have not found scholarly studies nor other information that confirmed that wood fiberboard based insulating board did actually contain asbestos.

References on Possible Asbestos Contaminants in Fiberboard Insulation Products

Some interesting citations pertinent to the question include both articles and patents that I include below

  • Altree-Williams, S., and J. S. Preston. "Asbestos and other fibre levels in buildings." Annals of Occupational Hygiene 29, no. 3 (1985): 357-363.
  • Cadotte, John E. "Manufacture of mineral fiberboard." U.S. Patent 3,297,517, issued January 10, 1967.
  • Coliection, Wood. "Wastes into Wood: Composites Are Promising New Resource. [PDF] [copy on file]
  • Coutts, Robert SP. "A review of Australian research into natural fibre cement composites." Cement and Concrete Composites 27, no. 5 (2005): 518-526.
    [Possibly a significant citation & source of confustion about the asbestos content of wood-product fiberobard sheets because this text uses the term "asbestos fiberboard" as do some others - Ed.
  • English, Brent. "Wastes into wood: composites are a promising new resource." Environmental Health Perspectives 102, no. 2 (1994): 168.
  • Falk, Bob. "Wood-Framed Building Deconstruction." Forest Products Journal 52, no. 3 (2002): 9.
  • Jamison, Danny G. "Method for using scrap rubber; scrap synthetic and textile material to create particle board products with desirable thermal and acoustical insulation values." U.S. Patent 5,439,735, issued August 8, 1995.
  • Ince, Peter J., and David B. McKeever. Recovery of paper and wood for recycling: actual and potential. Vol. 88. US Department of Agriculture, Forest Service, Forest Products Laboratory, 1995.
  • Ince, Peter J., and David B. McKeever. "Estimates of paper and wood recovery for recycling and potential for additional recovery in the United States." WOODFIBER plastic composites: virgin and recycled wood fiber and polymers for composites. Madison: Forest Products Society (1995): 144-154.
  • Kollmann, Franz FP, Edward W. Kuenzi, and Alfred J. Stamm. "Fiberboard." In Principles of Wood Science and Technology, pp. 551-672. Springer Berlin Heidelberg, 1975. [Significantly this article refers to the occasional blending of asbestos with wood fiber products.] Lundgren, S. Ake. "Hardboard as construction material—a viscoelastic substance." Holz als Roh-und Werkstoff 15, no. 1 (1957): 19-23.
  • Sebastien, P. M. A. G. A. G. J., M. A. Billon, G. Dufour, A. Gaudichet, G. Bonnaud, and J. Bignon. "Levels of asbestos air pollution in some environmental situations." Annals of the New York Academy of Sciences 330, no. 1 (1979): 401-415.
  • Selikoff, Irving John, and Douglas HK Lee. Asbestos and disease. Academic Press, 1978.
  • Stratton, J. C., and I. S. Walker. "Health and Safety Guide for Home Performance Contractors." (2012).
  • Wise, Steve H. "Production of fiberboard containing mineral fiber." U.S. Patent 3,093,533, issued June 11, 1963.

Reader Question: Does blackboard sheathing, fiberboard, Homasote, Celotex insulating board contain asbestos?

We i am curious about the black board? Our house was built in 1962 and I need to drill through the black board to run electrical! Some of it is super brittle and falling apart anyway. Was any of that stuff made with asbestos? What are chances it has asbestos in it? - Brett 9/4/2011

I was tearing off parts an outside wall connected to the garage to add insulation to the wall, after removing the plywood and tar paper I ran into Celotex fiber/black board.

I have a picture of it to upload if at all possible, but what I can see is that it is black fiber board with Celotex in yellow writing with patent pend. underneath the logo. The house was built in 1950 and I am concerned this product actually may contain asbestos. Is there any way you can confirm or deny this or point me in the right direction to find out. - Jon T. 11/5/2011

Reply: Asbestos is not an ingredient in fiberboard insulating sheathing. See the product description & MSDS information above

Brett and Jon: it's easy to drill through "black board" Homasote or Celotex type building insulating sheathing. Generally the product is made from wood fibers, not asbestos - See the insulating board MSDS data sheet quotations in the FAQ discussion just above.

Though I've heard rumor, not fact, claiming that some fiberboard insulating sheathing products contained asbestos, I have been unable to find an authoritative source that confirmed that worry for any of those products. Take a look at the insulating board MSDS data in the FAQ above about yard mulch and you'll see clear statements from the manufacturers on this matter.

Reader comment:

I only have to drill small hole to run wiring! Some of it's already crumbling and brittle! It's black on outside looks like wood inside. I too have not been able to find anything confirming or not confirming this concern! I'm stuck with new electrical to run and deciding if this is health issue or or not. Thank you again - Brett


Sounds as if the risk is nil, Brett. In addition to the comment we made above (wood fibers are not asbestos), you can minimize dust release by moistening the drilling area a bit. It's unlikely that there would be a measurable hazard from drilling a single wire-sized hole. Too, if you have a generic objection to even small amounts of dust from any building material, you have the option of HEPA vacuuming during and after drilling to keep the dust out of the air.

Reader Question: Is this a brown insulation board? I worry that it contains asbestos.

Brown insulation board and roof leak (C) Daniel Friedman Ben KohlbeckI know you guys know a lot about asbestos containing products and just wanted advice on a wood like fibre board I found in a cellar, I was worried it contains asbestos but just looks too dark to be to me and more like other wood fibre boards you discuss on your website. Any views would be appreciated. Picture attached! (feel free to republish as you like). - B.K. 06/29/2012


A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem - in the case of your photo it looks as if that area has been quite wet for some time - nice mushrooms growing - watch out for rotted ceiling joists or rafters.

It appears that the original ceiling was a brown fiberboard product that was later covered by drywall - visible in the left side of your picture. Your home is an old one - the roof sheathing boards visible where the ceiling has collapsed in from leaks were cut with a machine-operated pit saw. Depending on the building's location, that could be a structure built before 1900. Fiberboard products have been around in the U.S. since about 1858, though they were not widely used until the 1940's.

The brownboard in your photo looks to me like a wood fiber product. Depending on the age of the building and its location (in the U.S. ?)  that ceiling could have been originally installed using an insulating fiberboard from any of fourteen manufacturers, so there are indeed variations in both original color, and in color after wetting and age.

Can you tell me the thickness of the material? Insulating fiberboards were usually 15/32" thick, with a few 1/2" thick; Hardboard such as some Masonite products can be 1/4? or thinner, and are hard. In your photo the board looks thicker than that, but the way it is tearing left me to consider a hardboard product. I'd be glad for you to send me about 2 in a clean ziplok bag, so that I can examine it in the lab (pro-bono, no fee). Unfortunately though I won't be able to examine it closely until our lab returns to the U.S. in January.


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