Properties of FRT Plywood & inspection tips:

This document summarizes the history of the development and use of fire-resistant plywood roof sheathing in the U.S. and explains the issue of structural damage to roof sheathing where fire retardant plywood roof sheathing, or FRT plywood was used on buildings.

Bottom line: FRT-treated material can degrade seriously due simply to high attic temperatures. Special inspection and testing methods are available. The cost to remove and replace FRT plywood roof sheathing was significant. In addition, FRT plywood roofed buildings apparently did not receive the fire-spread resistance that was intended.

Requirements & Specifications for Fire Retardant Plywood Treatment for Roof Sheathing

What is FRT Plywood or Wood?

Fire-retardant-treated plywood or lumber is pressure-impregnated with chemicals to permanently inhibit combustion. This qualifies it for a lower flame-spread rating (at least as low as gypsum wallboard) and smoke developed index, and reduces its fire-hazard classification. (APA 2009)

FRT or flame resistant plywood is (or was) required by building codes for certain structures such as on either side of the fire wall between building units in multiple-living unit structures (apartments, condos, townhouses).

The earliest permitted use of FRT plywood in the U.S. was in the 1960s, allowed by building codes applied principally to states east of the Mississippi.

The first BOCA approval of FRT plywood for roof sheathing was in 1979.

This was an effort to permit omitting of more-costly through-roof parapet walls that were otherwise required to prevent the spread of fire between building units.

Our photo above shows the success of FRT plywood in preventing fire spread from one portion of a flaming building to the next.

[Click to enlarge any image]

Widespread use of FRT plywood began in the U.S. by 1980, and the first FRT failures were observed as soon as 1-3 years following initial construction.

Affecting 250,000 homes or more in the U.S., (Builder 1992), FRT plywood failures, and subsequently also some FRT wood framing (truss) failures were found to be most-rapid and serious where buildings were exposed to higher temperatures and humidity, though temperature is the greater factor in these failures.

FRT Plywood Problem: Structural Deterioration in Environments of Heat & Moisture

In the U.S. including New Jersey where this problem was first brought to our attention, FRT plywood roof sheathing products began to be widely used during the late 1970s and early 1980s (Barbel 1992), mostly in homes east of the Mississippi, and was used in construction up to 1988 (Kryakos 1994) or in a few sources, up to about 1990 (McLain 2017).

FRT deterioration problems were first "discovered" in New Jersey around 1987 and were found throughout the U.S. wherever FRT plywood was used in roof construction.

In the worst cases, roofs made with FRT plywood have required replacement. In these cases the wood had darkened, was very brash and brittle, and crumbled easily.

For the severely degraded roofs brought to our attention, service time has ranged from 3 to 8 years. The publicity generated from the problem has raised serious questions about the causes and extent of wood deterioration.

The magnitude of wood degradation depends on the particular fire retardant formulation used, the temperature levels attained in the roof system, and the presence of moisture. - (LeVan, USFPS, 1989)

The FRT deterioration problem was widely investigated by experts as you'll see in citations given at the end of this article, and was addressed by ASTM and other standards associations in North America.

FRT plywood was intended to deteriorate in response to a fire at around 400°F by charring to retard flame spread.

But in actual field experience it was found that the deterioration of FRT plywood occurs in response to the heat at temperatures as low as 150°F, commonly-experienced by roof sheathing from sun exposure and attic or roof-cavity temperatures was sufficient to so-weaken the plywood that someone walking on the roof could easily step right through the material. (Peterson 1990)

The effectiveness of the fire-resistant roof sheathing also was called into question.

As a substitute for vertical through-roof firewalls on multiple-dwelling buildings, the advent of FRT-plywood permitted omission of those more costly fire-walls that had to be built up extending through roof design.

The omission of that vertical through-roof extension simplified building roof construction thus reducing building cost as well as re-roofing costs.

Watch out: when inspecting a building for the presence of FRT plywood, before walking on the roof, be sure to first inspect the roof sheathing and framing from the attic or under-roof space.

Watch out: If you suspect or confirm that FRT plywood is in place on the roof, do not walk on that roof area as weakened plywood roof sheathing could give way, resulting in roof damage, even possibly a collapse, and severe personal injury.

Premature Degradation of Fire-Retardant-Treated (FRT) Plywood Used in Roof Decks

The following is adapted with permission from an original Fire-Retardant-Treated (FRT) Plywood article in Professional Roofing by Tom Bollnow, Professional Roofing, May 1999 p.62.

Q: Have there been any significant efforts made to eliminate premature degradation of fire-retardant-treated (FRT) plywood used as roof decks?

A. During the late 1980s, there was an outbreak of structural roof deck failures directly related to degradation of FRT plywood used as roof sheathing.

Because the potential for FRT ply- wood degradation still exists, roofing professionals should be knowledgeable about FRT plywood properties so the likelihood of degradation occurring can be reduced.

FRT plywood is produced by pressure treating plywood with fire retardant chemicals. During the mid 1980s, the search for lower hygroscopic (i.e., less moisture-absorbing) chemical compounds to treat plywood resulted in a change from ammonium sulfates that cause fastener corrosion to ammonium phosphate salts.

Ammonium phosphate salts with additional treatments using buffers, such as Borax, and organic and less acidic chemicals were developed to decrease fastener corrosion and raise the threshold temperatures of fire-retardant materials.

FRT plywood's structural strength changes from 10 percent to 20 percent after an initial pressure treatment procedure.

The drying process follows the pressure treatment procedure and is critical to achieving maximum product performance. Problems result if the kiln drying process is accelerated. Air drying causes fewer problems, but it is more time-consuming.

Products should be marked "KDAT" if kiln dried after treatment or "ADAT" if air dried after treatment.

3 Categories of Fire Retardant Treated Plywood

FRT plywood treatments are divided into three categories:

1. Exterior grade FRT Plywood
2. Interior Type A FRT Plywood
3. Interior Type B FRT Plywood

A roof deck typically will be interior Type A because it is not exposed directly to outside elements.

Type B treatments can cause excessive moisture to accumulate in wood, allowing chemicals to react with steel fasteners and connectors.

Building code authorities, such as the Building Officials and Code Administrators (BOCA) International Inc., have specific requirements for treatment processes and labeling.

For example, plywood must be manufactured according to American Wood Preservers Association (AWPA) standards, and the treatment process must be evaluated by BOCA Evaluation Services, National Evaluation Services or an AWPA-approved, independent agency.

3 Fire Retardant Chemicals & Their Effects on Plywood & Wood Framing

FRT chemicals that have been used to treat plywood and framing lumber that have been of particular focus include:

• DPF - dycyandiamide phosphoric acid formaldehyde - an organic salt fire retardant used on exterior plywood or framing products
• GUP - guanylurea phosphate - also referred to as boric acid, long and widely used for insect and rot resistance treatments, used as a commercial interior fire retardant on plywood and framing
• MAP - monoammonium phosphate, an inorganic salt fire retardant widely used in roofs whose plywood was found to fail early in the building's life

All three of these cause an acceleration in wood deterioration or strength loss compared with un-treated controls, but MAP was found to have a significantly greater effect than either of the two organic salt FR treatments. (Winandy 1990)

It is important to note that permanent thermal degradation eventually occurs for both treated and untreated materials exposed at 180°F. Furthermore, it is noteworthy that after thermally induced degradation has initiated (<21 days exposure) and eventually stabilized (>21 days exposure), the raw of strength degradation is similar between treated and untreated materials, even though there arc large differences in strength. (Winandy 1990)

In understanding the effect of these chemicals on wood building products it's worth noting

The results indicate that MAP-treated plywood is lower in bending strength than untreated plywood at all temperature and, as temperature increases, the rate of strength degradation is similar between untreated and MAP-treated plywood.

It was also noted that as relative humidity increased at 170°F, the rate of strength degradation increased.

However, the effect of relative humidity did not appear to be as influential as the effect of the temperature of exposure. (Winandy 1990)

Problems with FRT Plywood Degradation Can Extend to Framing

On older buildings where FRT plywood was used, attic heat and age was found to lead to deteriorated roof decks even where no actual fire had ever occurred.

[The] degradation process is directly associated with environmental conditions of temperature and humidity. The FRT chemicals react with wood during cyclical changes in temperature and humidity causing changes in pH such that the wood becomes brittle. This process is most commonly associated with plywood roof sheathing, where exposure to radiant heat is most significant. (Hodgin 2002).

Apparently the fire resistive treatment, intended to lead to a "surface charring" of the plywood to slow flame spread, also led to surface oxidation and deterioration. Often structural repairs will be required.

While FRT plywood seemed as if it was going to be a terrific product, it appears that high attic temperatures in some buildings caused early deterioration of the material.

In some cases the plywood became so soft that someone walking on the roof could simply step right through it. The material, as it was formulated in its problematic form, is no longer used in new construction but may still be found on some buildings.

Watch out: in some buildings roof structures included both FRT-treated plywood decking and also FRT-treated roof-support framing.

At Chesterfield Marlboro Technical College in South Carolina, the collapse of the roof of a building constructed in 1974 was found to be due to deterioration of both FRT plywood roof decking and FRT-treated roof trusses. Derek Hodgin, a P.E., and Andy Lee, a professor of Forest Product Resources at Clemson investigated the deterioration of FRT-treaded wood framing at the college. .

... a recent case study in South Carolina indicates that the effects on southern pine dimension lumber used in roof framing [and treated with fire retardant chemicals] can be equally dramatic. (Hodgin 2002).

Where will Fire Retardant Treated Plywood or Framing be Found?

On entry into the attic space of a multiple-dwelling structure such as attached town homes or condominiums, look first for the fire-wall that should have been built between the abutting units. In proper modern construction that firewall should extend from the foundation up through the occupied space and up through the attic space to at least the roof surface.

In that design, typically FRT plywood roof decking was used for four feet on either side of the firewall between building sections, and the firewall terminated just below the roof decking. You can see that design in the photo below.

The concrete block wall on the left of the photo is the fire-wall, and you can see that the plywood roof sheathing adjacent to the fire-wall looks different (like plywood) than the remaining roof sheathing (that is OSB in the right portion of the photo).

In more recent construction as well as in retrofit jobs intended to improve building fire safety you may see a double layer of fire-resistant drywall installed for as much as four feet against the roof sheathing on either side of the party wall or fire-wall between adjacent living units.

Look for FRT-treated roof sheathing (and possibly framing)

• On wood framed buildings that involve multiple occupancies (condominiums, offices, dormitories, commercial buildings, and other large multi-occupant buildings).
  
  These will be buildings classified in the IBC (International Building Code) as Type IIIA and IV
  
  Depending on the design, Building Types IIIA and IV ... interior walls, floors and roofs can be conventional untreated wood. Noncombustible exterior walls are required for these building types.
  
  The IBC, however, allows fire-retardant-treated wood for exterior walls as an option if the designer chooses to use wood walls. (APA 2009)
• Built in North America between 1960 and 1988
• Inspect for FRT in the building attic, found Installed as plywood roof decking, at fire walls or partitions between building sections or units, usually with the first four feet on either side of a fire partition between abutting building occupancy units
  
  Watch out: FRT may have been used in some buildings where no fire-walls extend up through the attic. We found this condition at some of the older Fox Hill condominiums in Poughkeepsie, New York.
• FRT damage prone wood may also be found as FRT-treated roof framing, particularly trusses
• FRT plywood may also be installed as exterior wall sheathing or partition wall sheathing in Type IIIA and IV Buildings (IBC).
• In the attic: notice the difference in roof sheathing appearance close-to and then more-distant from the partition or fire-wall.
  
  Look for areas of plywood that have darkened, particularly if roof sheathing plywood is more-dark than other areas of the roof deck more-distant from a fire wall or partition
  
  Look for significant color differences between plywood roof sheathing at the dividing fire wall and other plywood (or possibly not plywood but OSB) roof decking.
  
  The FRT plywood may be more darker: more black, gray, red, or brown than its neighbor.
  
  The FRT plywood may be visibly more deteriorated: you may see splits or open coarse wood grain on the exposed surface ply of the sheathing, or the plywood surface may appear abraded, rough, fuzzy.
  
  In more extreme FRT plywood damage we've seen an alligatored-crack pattern in which cracks in the surface plies not only follow the original wood grain but also cross the wood grain.
  
  You may see, as in our photo above, FRT for one or two truss or rafter bays on either side of the fire wall while the rest of the roof sheathing is another (less expensive) roof sheathing plywood or OSB.
• Outside: notice that the roof decking or sheathing appears to sag noticeably between rafters or trusses
  
  You may see actual deep depressions or sagging in the roof deck where someone has stepped onto a soft area of FRT plywood.
  
  Roof shingles may also be more-curled or damaged over these sagging roof areas.
  
  (Of course other causes of sagging roof decking could be present including use of thinner (3/8") plywood or leaks or other water damage to the roof. )
• Watch out: FRT plywood used as wall sheathing will not normally be accessible for detection by non-invasive visual inspection but you might infer the possibility of its use by noting the structure type, age, and use.

Can an Inspector Determine the Condition & Safety of Existing FRT Roof Decking or Framing?

OPINION: Yes and no.

Yes, a home inspector or building inspector or contractor can certainly observe visual deterioration that is advanced enough that an FRT plywood roof deck is sagging, delaminated, shedding, or visibly damaged, as she might also see roof truss failures if the trusses are FRT also.

No, a more-thorough, professional investigation of the condition of FRT roof sheathing and framing may require probing, mechanical testing, or chemical tests such as a measure of the plywood's pH. (Lebow 1999).

In our OPINION the very least required of an building inspector is the identification of the presence of FRT roof sheathing if there is access to the underside of the roof sheathing such as in an attic, and if visual evidence such as the presence of fire-walls, plywood stamps, variations in the appearance of plywood, and the building age combine to merit both an inspection for and a warning about the actual or potential presence of these materials.

Test protocols for FRT plywood are cited in several of the references given at the bottom of this page. We refer especially to

Winandy et als, THERMAL DEGRADATION OF FIRE-RETARDANT-TREATED PLYWOOD, Development & Evaluation of a Test Protocol [PDF] (2002) cited in more-detail below.

Fire-Retardant-Treated Plywood & Lumber Lawsuits

Early litigation appeared to begin with FRT roof failure cases in New Jersey but spread to other states, as we cite below.

• Anden Group, in 1990, was sued and required to pay $460,000 to repair condominium roofs in Falls Church, Va. (Builder Magazine, 1 April 1992)
• K Hovanian Co., Lawrenceville NJ, a worker was injured by falling through an FRT plywood roof. K. Hovnanian Co. sued on behalf of its 32 New Jersey developments after a section of crumbling roof in a Lawrenceville condominium gave way under two workers, injuring one of them. (NY Times & Chicago Tribune 1990)
• New Century Enterprises, Inc.,
• NVR, Inc. Ryan Homes Division
• Pulte Homes Corp. in 1992 sued Osmose Wood Products, received a $6.25 million jury award for damages over 1,800 roof failures in the Washington D.C. area (and elsewhere), in the largest award up to April 1992. (Builder Magazine, 1 April 1992)
  
  In the same year, Pulte also sued Hoover Treated Wood Products for FRT failure losses.
• Ryland Group Homes, Inc.,
• Winchester Homes, Inc.
• Peterson, Iver, FAULTY PLYWOOD SENDS LAWSUITES THROUGH ROOF [PDF] (1990) New York Times News Service, reported in the Chicago Tribune, 14 April, 1990, retrieved 2022/06/24, original source: https://www.chicagotribune.com/ news/ct-xpm-1990-04-14-9001310274-story.html
  Excerpt:
  A fire-retardant plywood that has become a standard building material in town house developments in the last decade has now been found to decompose after only a few years, leaving homeowners and builders with leaky and unsafe roofs and large repair bills.
  
  The plywood, called FRTP, for fire resistant treated plywood, has been used in the roofs of a million housing units east of the Mississippi, according to the National Association of Home Builders.
• Kyriakos, Marianne, CASES INVOLVING DEFECTIVE FRT PLYWOOD LINGER [PDF] (1994) The Washington Post, 24 Sept. 1994, retrieved 2022/06/24, original source: https://www.washingtonpost.com/archive/ realestate/1994/09/24/ cases-involving-defective-frt-plywood-linger/bc1a5f5b-d705-4d07-b762-2db1ffd04d89/
• Salmon, Jacqueliine L., SETTLEMENT REACHED in ROOFING CASE [PDF] (1992) The Washington Post, 7 November 1992, retrieved 2022/06/24, original source: https://www.washingtonpost.com/archive/ realestate/1992/11/07/ settlement-reached-in-roofing-case/28d54b21-78a2-4904-801e-d468476990a2/
  Excerpt:
  About 11,000 New Jersey homeowners with roofs constructed with fire-retardant-treated (FRT) plywood will pay at little as $200 each to have their roofs replaced under a sweeping settlement announced last week by the state.
  
  The $50 million settlement affects owners of homes built by New Jersey builder K. Hovnanian Enterprises and will be used as a model to determine the outcome of cases involving 24,000 other New Jersey homeowners who have FRT roofs, according to those involved in the negotiations. FRT plywood roof sheeting, which slows the spread of flames, was widely used on town houses and condominiums in the 1980s before it was discovered that it can deteriorate in hot attics.

Fire Retardant Treated Plywood Identifying Labels & Brands

In addition, each plywood piece must be labeled properly with its performance rating and design-strength adjustment values. FRT plywood must be used according to manufacturers' recommendations. It must be kept dry and used strictly within the parameters of design-load values.

Below: fire retardant plywood identifying stamp. [Click to enlarge any image]

Identification of and Current Applications of Modern FRT Plywood

In a "how to" article on equipment room fire safety design discussing FRT plywood backer boards for electrical panels, thanks to engineer Ronald Belleza de los Santos, datacom provides this FRT identification detail:

A Fire-Retardant-Treated backboard will be designated with a fire-rated stamp “branded” or “stamped” along the edge or center of the plywood—“UL FR-S Plywood 1780 R-7003.” Marine-grade plywood does NOT qualify even though it is saline “treated”—as it will have a different UL number.

FRT Plywood Brands in the U.S.

FRT Plywood Brands & Dates

Up to 1970

Hoover Treated Wood Products Co..

Hoover Universal, Inc.,

Osmose Wood PReserving, Inc.,

After 1970

Circle-M Wood Treating Co.

D-Blaze

Dri-Con

Flame Guard Fire Retardant

Flameproof LHC

Hoover Treated Wood Products, Inc. Hoover Universal, Inc.

Osmose Wood Preserving, Inc.

Protex

Notes to the table above

• Sources: (McLain 2017) cited in detail below and (Kyriakos 1994) cited above.
• More than 20 companies in the U.S. produced FRT plywood and/or wood framing products. In the 1990s Hoover was the largest U.S. FRT plywood treatment company. The company, facing an estimated $500. million in repair costs met with resistance from its insurance companies, according to company president Peter Reinhart. by 1992 roughly 100 lawsuits had been filed concerning FRT plywood failures.

How Fire Retardant Treated Plywood Works

Open flames' elevated temperatures activate fire-retardant chemicals that produce. low-level acids (i.e., acid hydrolysis) in FRT plywood.

The acids lower the temperature at which thermal degradation occurs, increase the amount of surface char and reduce the production of flammable volatiles (i.e., by-product gases that contribute to flame spread).

The results are a reduction of the flame spread across a surface and capacity to support combustion. When a flame is removed from FRT plywood's surface, the plywood will char but not burst into flames.

Chemicals that produce low-level acids causing fire-retardant effects also cause premature FRT plywood degradation at lower temperatures. Untreated plywood experiences no major problems at temperatures up to 200 F (93 Q. Roofing professionals should note that achieving fire retardancy at the expense of structural integrity is not desirable.

Acid hydrolysis and degradation can occur at lower elevated temperatures of about 130 F (54 C to 180 F (82 Q. Temperatures at the interface surface between a roof covering and deck can reach 200 F (93 X with 150 F (66 C commonly found.

As a result, degradation can occur at temperatures that are below open flame temperatures.

Fire-retardant-treated wood is defined in Section 2303.2 of the 2006 IBC as “any wood product which, when impregnated with chemicals by a pressure process or other means during manufacture, shall have, when tested in accordance with ASTM E 84, a listed flame-spread index of 25 or less and show no evidence of significant progressive combustion when the test is continued for an additional 20-minute period.

In addition, the flame front shall not progress more than 10.5 feet (3200 mm) beyond the centerline of the burners at any time during the test.”

The ASTM E 84 test is also called “The Tunnel Test” because the test material is suspended from the lid of a test chamber that is approximately 25 feet long by one foot high and 1-1/2 feet wide. (APA 2009)

This APA document (cited in detail below and provided as a PDF download) includes details about the flame spread test and the IBC 803 definitions of Class A, B, and C Flame Spread materials.

Current Uses of Fire-Retardant-Treated (FRT) Plywood

Fire retardant treated FRT plywood, while it is still a combustible material, has been chemically treated to provide a lower flame-spread rate than un-treated plywood used in building construction.

Our second photo of a contained spread of fire (left) illustrates the object of using this fire resistant roof sheathing.

The plywood industry states that the flame-spread rate of FRT plywood is at least as low as gypsum wallboard (although without specifying which fire-rated wallboard was used for comparison).

Current Definition of FRT Plywood

In the Uniform Building Code, Fire-Retardant-Treated Wood is defined as

... any wood product impregnated with chemicals by a pressure process or other means during manufacture, and which, when tested in accordance with UBC Standard 8-1 for a period of 30 minutes, shall have a flame spread of not over 25 and show no evidence of progressive combustion

Fire resistant or fireproof buildings and FRT wood use

According to the APA, and in accordance with the International Building Code (IBC), noncombustible buildings Types I and II (usually built of steel and concrete), allow fire-retardant-treated plywood and heavy timber construction in limited uses.

In buildings type IIIA and IV (less fire resistant than Types I and II), interior walls, floors, and roofs may be built of conventional, untreated wood. Non-combustible exterior walls (required for building types IIIA and IV) are required however. The IBC permits FRT wood for these exterior walls as a design option.

Factors Reducing the Deterioration of FRT Plywood

If FRT plywood is installed new or encountered during a recover situation, the use of light-colored shingles, a radiant-reflecting roof covering (e.g., white single-ply) or improved ventilation may diminish potential degradation.

These materials may lower temperatures at a roof deck's surface. Roofing professionals should use caution and precise documentation when confronted with FRT plywood roof decks to avoid repercussions if failures occur.

American Plywood Association Information about Fire Retardant Treated FRT Plywood

For a detailed, industry-provided and current description of Fire Retardant Treated FRT Plywood,

see FIRE-RETARDANT-TREATED (FRT) PLYWOOD [PDF] (2009) cited in detail below.

This document includes the types of construction where FRT plywood is used, specifies the proper type of fasteners used for FRT plywood, describes the burn-through resistance and design capacities of FRT wood, provides the FRT plywood treating process and test standards, outlines code-approved applications for FRT Plywood, and explains how to identify fire-retardant treated plywood. -- thanks to Arlene Puentes for assistance with this material.

Construction Alternatives Can Eliminate the Need for FRT Plywood

Roofing professionals should note that there are construction alternatives available that can eliminate the use of FRT plywood. But local codes (e.g., fire, building) first must be referenced to be sure the alternative construction is in compliance.

How fire spread is controlled where FRT plywood was or is not used?

These options include fully sprinkled interior systems; noncombustible decks; %-inch- (16-mm-) thick water- and fire-resistant gypsum board beneath untreated plywood; and fire walls that extend through a roof system on a multi tenant building (e.g., an apartment complex).

Alternative products to using FRT plywood as roof sheathing for the roof section covering the area of abutment of multiple living units have included

• masonry walls that penetrate the roof and
• fire-resistant drywall laminated on the under-side of the roof sheathing on either side of the wall.

Where these products and designs were used FRT plywood may have not been required.

Conventional Wood Frame Buildings and FRT Wood use vs Fire Sprinklers etc.

IBC building type V (conventional wood frame buildings) have the lowest fire resistance and are the least costly to construct.

Type V buildings may be constructed using conventional un-treated wood throughout the structure.

However the use of fire sprinkler systems, fire spacings (set-backs), and fire-resistant-rated walls, floors, and roofs, are required to obtain larger interior spaces.

Fire Retardant Plywood History, Research, Failures

• 1994 Standard Building Code, B704.4 TOWNHOUSE FIRE SEPARATION
  
  B704.4.1 Each townhouse shall be considered a separate building and shall be separated from adjoining townhouses by a party wall complying with B704.4.2 or by the use of separate exterior walls meeting the requirements of Table B600 for zero clearance from property lines as required for the type of construction. Separate exterior walls shall include one of the following: [code continues to list fire wall construction details)
• APA, Standard PS1, (1982), American Plywood Association, Tacoma WA
• APA, FIRE-RETARDANT-TREATED (FRT) PLYWOOD [PDF] (2009) American Plywood Association (APA), 7011 So. 19th St. Tacoma, Washington 98466, Tel: (253) 565-6600 or Product support help desk: 253-620-7400, email: help@apawood.org, representing the engineered wood industry, publication NO. K320, January 2009.
  
  Except:
  In addition, the treatment process itself may require a modification of the design capacities of the treated plywood. IBC Sections 2303.2.2.1 and 2303.2.2.2 require that “the effect of treatment and the method of re drying after treatment, and exposure to high temperatures and high humidities on the flexure properties of fire-retardant-treated soft- wood plywood shall be determined in accordance with ASTM D 5516.
  
  The test data developed by ASTM D 5516 shall be used to develop adjustment factors, maximum loads and spans, or both, for untreated plywood design values in accordance with ASTM D 6305. Each manufacturer shall publish the allowable maximum loads and spans for service as floor and roof sheathing for its treatment.”
• Arnold, Jim. LARGE BUILDING FIRES AND SUBSEQUENT CODE CHANGES [PDF] Clark County Department of Development Services, Building Division, 2005. Department of Development Services Building Division 4701 W. Russell Road y Las Vegas NV 89118 (702) 455-8040, retrieved 2018/12/05 original source: http://ddwei.info/pdf/subsequent/0.pdf
• ANSI/UL 263, Standard for Fire Tests of Building Construction and Materials, Underwriters Laboratories Inc., 2003.
• ANSI/UL 723, Standard for Test for Surface Burning Characteristics of Building Materials, 2003, Revised 2005.
• ASTM, Annual Book of ASTM Standards, 1986, American Society of Testing and Materials, Philadelphia PA
• ASTM 1987, Section 4, Construction, Vol. 4.09, Wood. ASTM D-198-84, ASTM D-271j8-76, ASTM D-2719-76, ASTM D-2898-81, ASTM D-3043-76, ASTM D-3044-76, ASTM D-3201-86, ASTM D-3500-76, ASTM D-3501-76, ASTM D-4671-88, Op. Cit.
• AWPA, Plywood fire-retardant treatment by pressure processes (1987), Standards C20 & C27, Society of American Wood Preservers, Inc. 7297 Lee Highway, Unit P Falls Church, VA 22042 (403) 237-0900
• Barbel, Neal J., PREMATURE DETERIORATION OF FIRE-RETARDANT TREATED PLYWOOD [PDF], supporting House Joint Resolution No. 238 - 1992, Commonwealth of Virginia, Department of Housing and Community Development, Jackson Center, 501 N. Second St., Richmond Va 23219, December 22, 1992,
  
  Excerpts: House Joint Resolution No. 238 passed by the 1992 General Assembly directed the Department of Housing and Community Development to examine and report on a number of issues associated with the use of fire-retardant treated CFRT) plywood.
  ...
  This study on the premature deterioration of fire-retardant treated plywood used as roof sheathing was conducted by the Department of Housing and Community Development in response to House Joint Resolution 238 of the 1992 General Assembly.
  
  The study requested the Department to develop a particular protocol to determine the structural characteristics and durability of the products and to give consideration as to whether a separate five-year warranty period should be enacted.
• Bueche, David G., NFPA CODE PROVISIONS AND FIRE-RETARDANT-TREATED WOOD [PDF] (2013), New Developments in Structural Engineering and Construction Yazdani, S. and Singh, A. (Eds.) ISEC-7, Honolulu, June 18 –23, 2013
  Excerpt:
  
  This paper examines these National Fire Protection Association (NFPA) codes and their referenced standards.
  
  It specifically addresses how fire-retardant-treated wood (FRTW) can be used in building construction and examines a few case histories demonstrating the use of FRTW in lieu of noncombustible building elements.
• LeVan, Susan & Mary Collet, CHOOSING and APPLYING FIRE-RETARDANT PLYWOOD AND LUMBER for ROOF DESIGNS [PDF] (1989) U.S.D.A., Forest Service, Forest Products Laboratory, FPL-GTR-6
• Eickner, Herbert, "Fire-retardant treated wood", Journal of Materials 1966 1(3): 625-644
• Fire Retardant Treated Wood/ Chemical Manufacturers Council 7297 Lee Highway, Unit P Falls Church, VA 22042 (703) 237-0900
• Freytag, Dylan, Keith Kesner, Randall W. Poston, and Kenneth Bondy. "WHEN BAD THINGS HAPPEN to GOOD [BUILDINGS] [PDF] Special Publication 291 (2013): 1-14.
• Gosselin, Guy C. Structural Fire Protection: Predictive Methods. Institute for Research in Construction, National Research Council of Canada, 1987.
• Gosselin, Guy Charles, and Tiam Tjoan Lie. Provision of Fire Resistance: Evolution of Design Approaches. Vol. 1. National Research Council Canada, Institute for Research in Construction, 1987.
  Langenbach, R. "Better than Steel?(Part 2): Tall Wooden Factories and the Invention of “Slow-burning” Heavy Timber Construction." Structures and Architecture: New concepts, applications and challenges (2013): 122.
• Heyer, Otto C. "Study of temperature of wood in parets of houses throughout the United States", Res. Note-012 1963, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison WI
• Hodgin, Derek A., and Andy WC Lee. COMPARISON OF STRENGTH PROPERTIES AND FAILURE CHARACTERISTICS BETWEEN FIRE-RETARDANT-TREATED AND UNTREATED ROOF FRAMING LUMBER AFTER LONG-TERM EXPOSURE:: A South Carolina case study. [PDF] (2002) Forest products journal 52, no. 6 (2002): 91-94.
  Abstract excerpts:
  ... This degradation process is directly associated with environmental conditions of temperature and humidity. The FRT chemicals react with wood during cyclical changes in temperature and humidity causing changes in pH such that the wood becomes brittle. This process is most commonly associated with plywood roof sheathing, where exposure to radiant heat is most significant.
  
  However a recent case study in South Carolina indicates that the effects on southern pine dimension lumber used in roof framing can be equally dramatic. This study included strength testing of both FRT and untreated roof framing lumber after 22 to 31 years of exposure.
  
  Analysis of modulus of elasticity (MOE) and the bending modulus of rupture (MOR) of these samples revealed no appreciable loss of bending strength in the untreated lumber. In contrast, the treated wood samples had significant losses in both MOE and MOR. The failure of the FRT wood samples occurred suddenly with a marked absence of toughness, which is a reflection of their brittle condition.
• International Building Code section 202 & section 706
  
  
• Kryiakos, Marianne, "Cases Involving Defective FRT Plywood Linger", The Washington Post, 24 September 1994. Retrieved 2018/12/05,original source: https://www.washingtonpost.com/archive/realestate/1994/09/24/cases-involving-defective-frt-plywood-linger/bc1a5f5b-d705-4d07-b762-2db1ffd04d89/?utm_term=.a1c46213d20d
  
  Excerpt: FRT plywood ended up on the roofs of thousands of condominiums and town houses built between 1976 and 1988, mostly east of the Mississippi.
• Lebow, Stan T., and Jerrold E. Winandy. "Effect of fire-retardant treatment on plywood pH and the relationship of pH to strength properties." Wood Science and Technology 33, no. 4 (1999): 285-298.
  Abstract:
  This paper investigates the relationship between wood pH and the strength properties of fire-retardant-treated (FRT) plywood, as it is affected by fire-retardant (FR) formulations, processing variables, and extended high temperature exposure conditions. The objectives of this study were to
  
  (1) identify the effect of post-treatment kiln-drying temperature, followed by high temperature exposure, on wood pH;
  
  (2) identify the effect of various mixtures of FR components, followed by high temperature exposure, on wood pH;
  
  (3) determine if treatment effects on strength and pH are affected by plywood thickness; and
  
  (4) quantify the relationship between changes in wood pH and strength loss and whether pH can be used as a predictor of strength loss.
  
  Results indicate that the differences in pH resulting from the initial re dry temperature became insignificant after extended periods of high temperature exposure.
  
  All FR treatments studied caused large, rapid decreases in pH, with the most rapid decreases occurring with formulations containing phosphoric acid.
  
  Additions of borate compounds, especially disodium octaborate tetrahydrate (Timbor), produced a measurable buffering effect that slowed or lessened the decreases in pH.
  
  No differences in the effect of FRT on the wood pH-strength relationship were noted between the two plywood thicknesses evaluated.
  
  A strong relationship was noted between changes in pH of the plywood and reductions in strength and energy-related properties.
  
  These findings suggest that the pH of FRT plywood is a good indicator of its current condition and may have potential as a predictor of future strength loss as the plywood is subjected to elevated in-service temperatures.
• Lebow, Stan T., and Jerrold E. Winandy. THE ROLE OF GRADE AND THICKNESS IN THE DEGRADATION OF FIRE RETARDANT-TREATED PLYWOOD [PDF] Forest products journal 48, no. 6 (1998): 89.
  
  Abstract:
  In some cases, fire-retardant-treated plywood used since 1980 for roof sheathing has rapidly degraded and failed, apparently because of thermally induced acid hydrolysis.
  
  This study sought to determine whether plywood grade or thickness influences the manner in which fire-retardant treatment (FRT) and subsequent high-temperature exposure affects the strength properties of plywood.
  
  The effects of FRT were evaluated on two thicknesses and three commercial grades of southern pine plywood as well as plywood constructed from nearly defect-free N-grade veneer. Specimens were treated with monoammonium phosphate (MAP), then subjected to exposure at 66°C (150°F) and 75 percent relative humidity for either 30, 60, or 90 days.
  
  Modulus of rupture (MOR), work to maximum load (WML), and modulus of elasticity (MOE) of the specimens were evaluated.
  
  Results suggest that the rate of plywood degrade resulting from FRT, redrying, and subsequent high-temperature exposure is largely independent of plywood quality or grade. Although the initial strength loss caused by FRT and redrying appeared greater for the thinner plywood, degrade during subsequent temperature exposure appeared to be independent of plywood thickness.
  
  Thus, it appears that findings from previous studies on thermal degrade using high quality, N-grade plywood are readily applicable to commercial grades and thicknesses.
  
  Evaluation of the effects of knots and voids on MOR revealed that these defects are only partially responsible for the difference in bending strength among specimens.
• LeVan, Susan L., R. J. Nagel, and J. W. Evans. MECHANICAL PROPERTIES OF FIRE-RETARDANT-TREATED PLYWOOD AFTER CYCLIC TEMPERATURE EXPOSURE [PDF] (1996) US Forest Products Journal 46, no. 5 (1996): 65.
  Abstract:
  Some fire-retardant-treated (FRT) plywood used as roof sheathing has demonstrated loss of strength in service conditions. Research at the Forest Products Laboratory is aimed toward identifying the failure mechanisms of FRT wood, the chemicals that contribute to wood degradation, the temperature levels at which degradation occurs, the influence of moisture content (MC), and the correlation between these factors and the rate of degradation.
  
  To date, these efforts have led to the development of constant temperature test regimes for both plywood and lumber (ASTM D 5516-1994, and D 5664-1995, respectively).
  
  The objective of the research addressed here is the determination of how well constant temperature cycles relate to actual cyclic in-service temperature fluctuations. In this study, a special grade of southern pine plywood was treated with two fire-retardant chemicals and subjected to a cyclic temperature variation from room temperature to 65°C at two targeted MC levels, 6 and 12 percent.
  
  Results indicate that modulus of elasticity (MOE) and modulus of rupture (MOR) were relatively unchanged. The MOR values indicated a slight negative trend at both targeted MC levels, although the MOR values for the 12 percent specimens were slightly less than the MOR values for the 6 percent specimens.
  
  The most affected strength property was work to maximum load. The treated material showed a greater tendency for degrade than did the untreated material. In comparison with data from a plywood study using 65°C and 12 percent MC at constant temperature exposure, cyclic exposure appears to be less severe than constant temperature exposure. However, uncertainty regarding the internal temperature of the plywood could account for the difference in severity.
• LeVan, Susan, Robert Jon Ross, and Jerrold E. Winandy. EFFECTS OF FIRE RETARDANT CHEMICALS ON THE BENDING PROPERTIES OF WOOD AT ELEVATED TEMPERATURES [PDF - book] US FPS, Vol. 498. US Department of Agriculture, Forest Service, Forest Products Laboratory, 1990.
• LeVan, Susan, & Mary Collet, CHOOSING AND APPLYING FIRERETARDANT-TREATED PLYWOOD AND LUMBER FOR ROOF DESIGNS [PDF] (1989) Gen. Tech. Rep. FPL-GTR-62. Madison, WI: U.S. Department of
  Agriculture, Forest Service, Forest Products Laboratory. 11 p., retrieved 2018/12/05, original source: https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr62.pdf
  Excerpt from Introduction:
  
  For certain applications, building codes and insurance companies permit fire retardant-treated wood to be used as an alternative to noncombustible materials. Fire retardants drastically reduce the rate at which flames travel across the wood surface, thereby reducing the capacity of the wood to contribute to a fire.
  
  In some situations, the use of fire-retardant-treated (FRT) plywood as roof sheathing has resulted in a problem: the wood loses strength through thermal degradation. Although available information indicates that the frequency at which this problem occurs is low in relation to the volume of FRT material in use, it also indicates that significant degradation can occur with some fire retardant-treatment formulations, in specific installations, and under the right conditions.
  
  The combination of elevated temperatures caused by solar radiation, type of fire retardant chemicals, and moisture can prematurely activate the fire retardant to do what it is designed to do: lower the temperature at which thermal degradation occurs, thereby increasing the char and reducing the production of flammable volatiles.
  
  These chemical changes, which occur at temperatures lower than those at the roof covering-sheathing interface, are responsible for the strength degradation of FRT plywood used as roof sheathing.
• LeVan, Susan L. "Chemistry of fire retardancy." Advances in chemistry series (1984).
• LeVan, Susan L. "Chemistry of fire retardancy." in Chemistry of Solid Wood, Rowell, Chapter 4, Series 207, Roger M. (ed), American Chemical Society, Washington D.C.
• McLain, Charles Joseph, AIA, When Bad Things Happen to Good BUildings: Red Flags in Property Condition Assessments, [book] (2017) Mclain Consulting Services, Inc., 3579 E. Foothill Blvd. #513, Pasadena CA 91107 USA, ISBN 978-1537094779, privately published book provided to InspectApedia.com by the author.
• McIntyre, Craig R., Ph.D., ASTM STANDARDS for FIRE RETARDANT WOOD [PDF] Original title: "FIRE [Retardants] Committee D07 Answers the Alarm" (2003) in ASTM Standardization News, June 2003, retrieved 2018/12/05, original source: https://www.astm.org/SNEWS/JUNE_2003/mcintyre_jun03.html
  
  A History of FRT Plywood in the U.S. is given in this excellent article from which we include some key Excerpts:
  
  Generally, Joseph Louis Gay-Lussac is credited with the development of fire retardants for wood when in 1820 he proposed treatments with ammonium phosphates and borax.
  
  ... These standards have given specifiers the needed confidence to again use fire retardant treated wood.
  
  In a definitive series of reports from 1930 to 1935, researchers at the USDA Forest Products Laboratory (FPL) investigated about 130 different inorganic fire retardant formulations.
  
  They found that diammonium phosphate was the most effective for reducing flame spread while monoammonium phosphate, ammonium chloride, ammonium sulfate, borax and zinc chloride were also active.
  
  However, many of the tested chemicals were later found to also have associated problems of high cost, corrosion, hygroscopicity, strength reduction or glow promotion. Therefore, other approaches were needed.
  
  By the 1950s, there were several formulations in commercial use for pressure treating wood. (Fire retardant coatings were also being investigated, but their acceptance and regulation lagged behind that of pressure-treated products.) All of these formulations were inorganic combinations blended to achieve a reasonable compromise of cost and acceptable performance.
  
  By the 1960s, three formulations became dominant and were used extensively for interior purposes for the next 20 years.
  
  Exterior formulations were introduced in the late 1960s for protection of products such as shingles, shakes, siding or scaffold planking that are exposed to the elements. These systems were based on a different chemistry in that polymers were formed within the wood. The polymers encapsulated the other fire retardant ingredients and rendered them leach resistant.
  
  The use of fire retardants climbed very slowly in the United States until the 1960s (Figure 1).
  
  Then from 1960 to 1970, the use quadrupled as there was an increased awareness of the considerable safety benefits of fire retardants.
  
  However, the emergence of corrosion, hygroscopicity and strength problems began to plague the industry and the market grew only slightly until 1980. The market suffered a downturn through the early 1980s even though building code changes were being implemented that opened up new uses for fire retardant treated wood.
  
  In the early 1980s, second-generation fire retardants were introduced to address the corrosion and hygroscopicity problems of the first generation inorganic formulations.
  
  These second-generation products were of two types. One formulation blended a nitrogen-phosphorus organic compound with boric acid. The other second-generation formulations were based on ammonium polyphosphates with or without various additives in small quantities. The additives included boric acid, borax, moldicides and others that augmented their performance.
  
  Strength Issues [of FRT treated plywood]
  
  With the introduction of the second-generation products, there was concern on the part of designers and specifiers that the generic strength reductions used for the previous fire retardants would no longer be applicable to the new products.
  
  Accordingly, in 1984, the National Design Specification for lumber was revised to require that the fire retardant producers supply design reduction factors and in 1986, a testing protocol for matched treated and untreated lumber was issued to determine NDS values. In 1987, the Plywood Design Specification was similarly revised to require design values from the producers but no testing protocol was specified.
  
  In the course of development of the NDS test protocol, it was suggested that elevated temperature testing be included but the protocol did not require such testing.
  
  Thus, in the late 1980s, there was no accepted protocol for testing either lumber or plywood at elevated temperatures. In the 1950s and ’60s, FPL researchers had shown that elevated temperatures and humidities can impact wood strength but their work was generally done at temperatures that seemed far above those occurring in structures.
  
  However, in the late 1980s, reports began to surface that some of the second-generation formulations were experiencing strength loss in high temperature applications such as roof sheathing.
  
  After the initial concern that all second-generation products were involved, it was found that problems were occurring with only some formulations.
  
  Litigation ensued and further investigations revealed that high humidity conditions frequently existed in problem installations. Numerous causes were alleged for the strength problems and the end result was that the overall market for fire retardants was severely impacted.
  
  An ASTM task force quickly developed a test protocol based on the FPL report and submitted it to D07 for consideration as an emergency standard.
  
  In late 1991, the test protocol was accepted as ES 20, Test Method for Evaluating the Mechanical Properties of Fire-Retardant Treated Softwood Plywood Exposed to Elevated Temperatures.
  
  This protocol eventually became D 5516, Test Method for Evaluating the Flexural Properties of Fire-Retardant Treated Softwood Plywood Exposed to Elevated Temperatures.
  
  These tests were developed under the ASTM consensus process by government, academic and industry researchers and quickly adopted by building codes and other regulators. The result is that several products are currently available that give excellent strength performance.
  
  In fact, new fire retardants entering the market essentially undergo testing by the above methods prior to acceptance into the stream of commerce.
  
  The ASTM process helped restore market stability and substantial growth in fire retardants has occurred in the last decade.
• National Forest Products Association 1250 Connecticut Avenue, NW Suite 200 Washington, DC 20036 (202) 463-2700
• NFPA 220, Standard on Types of Construction, 2009 edition.
• NFPA 221, Standard for High Challenge Fire Walls, Fire Walls, and Fire Barrier Walls, 2009 edition.
• NFPA 251, Standard Method of Tests of Fire Resistance of Building Construction and Materials, 2006 edition.
• NFPA 255, Standard Method of Test of Surface Burning Characteristics of Building Materials, 2006 edition.
• NFPA 703, Standard for Fire Retardant – Treated Wood and Fire-Retardant Coatings for Building Materials, 2009 edition.
• NFPA 5000, Building Construction and Safety Code, 2009 edition.
• NFPA, National design specifications for wood construction, 1986, NFPA, Washington D.C.
• Peterson, Iver, "A Plywood Used in Many Homes Is Found to Decay in a Few Years" (1990), The New York Times, 11 April 1990, retrieved 2018/12/05, original source: https://www.nytimes.com/1990/04/11/nyregion/a-plywood-used-in-many-homes-is-found-to-decay-in-a-few-years.html
  
  Excerpts:
  
  A fire-retardant plywood that has become a standard building material in town house developments in the last decade has now been found to decompose after only a few years, leaving homeowners and builders with leaky and unsafe roofs and large repair bills.
  
  The plywood, called F.R.T.P., for fire resistant treated plywood, has been used in the roofs of a million housing units east of the Mississippi, according to the National Association of Home Builders.
  
  Since the problems were first discovered in New Jersey several years ago, scores of lawsuits have been filed against makers, suppliers and insurers.
  
  ...One plaintiff in the suits is Millponds, a 400-unit town house development in Marlboro Township, N.J., where all of the fire-retardant parts of its roofs are in various stages of decay, said the homeowner's association's lawyer, E. Richard Kennedy. Mr. Kennedy is credited with having first traced the problem to the wood itself in 1987.
  
  Heat built up on roofs by the sun - at temperatures as low as 150 degrees Fahrenheit - sets off the fire-stopping acidic reaction that the wood's designers intended to happen only at the temperatures of an actual house fire, about 400 degrees.
  
  The heat and chemicals attack the cellular structure of the wood, causing it to weaken.
  
• Professional Roofing May 1999, p. 62, provided some of the original information for this article. Photograph, adaptation, edits and additions by the website editor, Daniel Friedman
• Shafizadeh, F., "Pyrolysis and combustion" in Chemistry of Solid Wood, Series 207, Chapter 13, Rowell, Roger M. (ed), American Chemical Society, Washington D.C.
• Stern, Henry, "Breakdown of Plywood Prompts Suits" The Washington Post, 14 April 1990, retrieved 2018/12/05, original source: https://www.washingtonpost.com/archive/realestate/1990/04/14/breakdown-of-plywood-prompts-suits/21a793f0-e5b0-4e06-9594-7f5e9c2b6018/?noredirect=on&utm_term=.480b851c00fb
  
  Excerpt:
  
  Builders primarily used the fire-resistant treated plywood in town houses during the housing boom of the early 1980s, said Bill Young, the consumer affairs director for the National Association of Home Builders.
  
  Builders in other parts of the nation used a code that had not yet permitted use of the treated plywood, also known as FRTP, he said.
  
  ... two workers were injured at a condominium in the town of Lawrenceville when a roof gave way ...
• Tang, W.K. "Effect of inorganic salts on pyrolysis of wood, alpha-cellulose and lignin determined by thermogravimetry", Research Paper, 1967, U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, Madison WI
  Abstract excerpt:
  
  Dynamic thermogravimetric analyses were conducted under vacuum on pyrolysis of wood, of alpha-cellulose, and of lignin, untreated and treated with 2 percent by weight of five inorganic salts.
  
  Data for weight loss and for rate of weight loss were obtained to indicate the principal decomposition ranges for the wood and the wood components, the effect of the chemicals on volatilization at various temperature ranges, and the kinetics of the decomposition reactions.
• Wang, Fengqiang, Qingwen Wang, and Xiangming Wang, PROGRESS IN RESEARCH ON FIRE RETARDANT–TREATED WOOD AND WOOD-BASED COMPOSITES: A CHINESE PERSPECTIVE [PDF] Forest Products Journal 60, no. 7 (2010): 668-678.
  
  Abstract: Research on fire retardant–treated wood and wood-based composites has been conducted in China for over two decades.
  
  Although many kinds of fire retardants for wood and wood-based composites have been studied, the focus is still mainly on compounds or mixtures containing phosphorus, nitrogen, and boron, which can be used in a water solution for solid wood impregnation. Fire-retardant treatment methods for wood-based panels are either pretreatment of veneers, fibers, particles, or strands before hot pressing or impregnation of waterproof panels with fire-retardant solutions.
  
  Though attempts have been made in laboratories and factories to mix the fire retardants with glues, it has proven very difficult to spray the glue smoothly and to deliver effective amounts of fire retardants during the manufacture of panels. The mechanisms of phosphorus–nitrogen–boron fire retardants have been investigated systematically.
  
  The results indicate that the phosphorus–nitrogen compounds and the boron compounds are highly synergistic in effective fire-retardant formulations. The catalytic charring effect of a fire retardant on wood is a key factor in its efficacy. A chemical fire-retardant mechanism for boric acid is also proposed.
  
  Research on fire retardants for wood–plastic composites has been attracting more attention in recent years; however, most results are preliminary because of the difficulty in identifying or formulating a fire-retardant system that is effective for both wood and plastics. Only preliminary research has been conducted on smoke suppression for wood; innovative efforts will be needed to conduct further research.
• Waring, Bradish J., THE HAZARDS of FIRE RETARDANT TREATED (FRT) WOOD [PDF] , retrieved 2018/12/05, original source: https://www.bestlawyers.com/Content/Downloads/Articles/14742.pdf
  Excerpt from conclusion:
  
  For more information on Fire Retardant Treated (FRT) Wood, log onto our web site at bwaring@nexsenpruet.com The Bottom Line The hazards associated with the FRT problem are real and should not be overlooked by property managers, owners and others who have responsibility for building maintenance.
  
  If an inspection reveals the presence of FRT lumber or plywood sheathing, a complete structural analysis by a competent structural engineer should be undertaken to determine the extent of any damage and loss of integrity of the wood. If necessary, immediate steps should be taken to secure the structure from a safety standpoint.
  
  In extreme cases, the building may have to be vacated. Thereafter, an assessment can be undertaken to determine the manufacturer(s) of the particular FRT and a complete damages evaluation can be conducted.
  
  Oftentimes, litigation against the manufacturers and/or others involved in the construction of the project results.
  
  Website: www.nexsenpruet.com Nexsen Pruet, LLC in Charleston, SC. Email: bwaring@nexsenpruet.com
• UL, Fire Resistance Directory, 2007 Underwriters Laboratories.
• White, Robert H. "Oxygen index evaluation of fire-retardant-treated wood." Wood science. Vol. 12, no. 2 (Oct. 1979): Pages 113-121 (1979).
  
• Winandy, Jerrold E., Susan L. LeVan, Robert J. Ross, Scott P. Hoffman, and Craig R. McIntyre. THERMAL DEGRADATION OF FIRE-RETARDANT-TREATED PLYWOOD, Development & Evaluation of a Test Protocol [PDF] (2002) US Department of Agriculture, Forest Service, Forest Products Laboratory, 2002.
  Abstract:
  Although untreated plywood has given satisfactory performance as roof sheathing for more than 50 years, some fire-retardant-treated plywood products have not performed satisfactorily in recent years.
  
  Thermally induced in-service failures have occurred with some fire-retardant-treated plywood roof sheathing. This paper describes the development and evaluation of a new test protocol for screening potential fire retardant treatments for plywood that is continuously or periodically exposed to elevated temperatures.
  
  In the protocol, untreated and monoammonium phosphate-treated Southern Pine plywood specimens were exposed to various exposure temperatures and durations under steady-state environments of 130°F (54°C)-73 percent relative humidity (RH), 150°F (65°C)-76 percent RH, 170°F (77°C)-79 percent RH, or 170°F (77°C)-50 percent RH. All specimens were mechanically tested in either bending or tension.
  
  Monoammonium-phosphate-treated plywood had lower bending and tension strength than did untreated plywood at all temperatures. The strength degradation rate of untreated and treated plywood increased as exposure temperature increased and appeared constant for any treatment-temperature combination (that is, linear over time).
  
  The strength degradation rate was greater at 170°F (77°C)-79 percent RH than at 170°F (77°C)-50 percent RH for both untreated and treated plywood. Within the RH limits studied, the magnitude of the RH effect did not appear to be as influential as the temperature effect. The results indicate the protocol provides an effective screening method for comparing the effects of extended exposure to elevated temperature on strength of untreated plywood and plywood treated with commercial fire retardant formulations.
  
• Winandy, J. E. 2001. Thermal Degradation of Fire-Retardant-Treated Wood: Predicting Residual Service Life. [PDF] Forest Prod. J. 51(2): 47-54.Winandy, J. E. 2001. Thermal Degradation of Fire-Retardant-Treated Wood: Predicting Residual Service Life. Forest Prod. J. 51(2): 47-54.
• Winandy, J.E., S.L. Levan, R.J. Ross, S.P. Hoffman and C.R. McIntyre. 1991. THERMAL DEGRADATION OF FIRE-RETARDANT-TREATED PLYWOOD: DEVELOPMENT AND EVALUATION OF A TEST PROTOCOL [PDF] (1991) Res. Pap. FPL-RP-501, U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory, p. 21.
  Abstract:
  The applicability of using the oxygen index test (ASTM D 2863-76) to obtain an indication of the relative flammability of fire-retardant- treated wood products was investigated. The oxygen index is the minimum percentage oxygen that is required to maintain flaming combustion of a specimen under specified laboratory conditions. ...
  
  Specimens from nine boards of southern pine were tested to obtain oxygen index values for untreated wood and wood at two treatment levels of diammonium phosphate. Next, untreated southern pine specimens were tested for the effects of grain direction, MC, and thickness of specimen.
  
  Finally, specimens from a single sheet of Douglas- fir plywood were treated with eight chemicals at four treatment levels and tested for oxygen index.
  
  The plywood oxygen index results were compared with available data for the fire tube, modified Schlyter, and 8-foot tunnel tests.
  
  The results show that the oxygen index test can be used as an indication of the flammability of a fire-retardant-treated wood sample relative to other fire-retardant-treated and untreated wood products, the results for the untreated and treated samples showed a range of 22 to 78 and an average coefficient of variation of 3 percent.
• Winandy, Jerrold E. FIRE-RETARDANT-TREATED WOOD: EFFECTS OF ELEVATED TEMPERATURE AND GUIDELINES FOR DESIGN [PDF] (1990) Wood Design Focus 1, no. 2 (1990): 8-10.
  Abstract:
  Fire-retardant-treated wood is an important component of nonresidential commercial and multifamily constructions. Research has shown that not all fire-retardant-treated wood exhibits similar performance attributes.
  
  Some formulations may cause thermally induced degradation of the wood in service. This paper briefly discusses the causes of the strength reductions and presents tentative guidelines for using fire-retardant-treated lumber and plywood.
• Winandy, J.E., "Effects of treatment and redrying on mechanical properties of wood" (1998) in M. Hamel (ed.) Wood protection and techniques and the use of treated wood in construction. FPRS Proceedings 48358, Forest Products Research Society, Madison, WI p. 54-62
• Yalinkilic, M.K., Su, W.Y., Imamyra, Y., Takahashi, M., Demirci, Z. and Yallnkilic, A.C., 1998. Boron effect on decay resistance of some fire-retardant coatings applied on plywood surface. Holz als Roh-und werkstoff, 56(5), pp.347-353.
  Abstract excerpt:
  Boron effect on decay resistance of some fire-retardant coatings applied on plywood surface was studied. Boric acid (B) was mixed into aqueous trimethylol melamine (TM) solution to increase the fixation in wood.
  
  ... Surface characteristics of decayed specimens were consistent with the determined values of mass losses caused by fungal attack. TMB and TMDB coatings were remarkably effective in maintaining sound surface properties after exposure to weathering and decay fungi.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

How do I know if my plywood is Class A or Class B?

How do I know if my plywood paneling is a class A or B? On 2019-03-08 by dana

Reply by y (mod) -

Dana

To identify a specific plywood product and thus its fire classification you would look for the stamps or markings on the plywood itself.

If you can't find that information you're stuck with having to find the original purchase or bill of sale and plywood supplier and to trace that information backwards through the supplier themselves.

When did FRT plywood come to the market?

What year did FRT come to the market, especially in NJ? - On 2018-12-05 by A Bartolomucci

Reply by (mod) -

Fire retardant treated wood as a very long history A.B. dating from before 1900.

The first BOCA approval of FRT plywood for roof sheathing was in 1979.

In the U.S. including in your state of New Jersey FRT plywood roof sheathing products began to be widely used during the late 1970s and early 1980s. (Barbel 1992)

FRT deterioration problems were first "discovered" in New Jersey around 1987. FRT had been on the market for more than a decade prior to that.

I already have some historical citations at the end of the article above. I'll go through our library and add some additional detail.

You may need to clear your browser cache and wait a few hours to see that added information.

How do we repair Delaminated FRT Plywood?

what is the preferred method of repairing delamination FRT is there a known patching material? to be applied from the inside? - On 2017-02-02 by Sam

Reply by (mod) - re-roof down to the rafters

Fire retardant treated wood that hs delaminated needs to be replaced, which means a re-roof job down to the rafters. I don't advise other shortcuts like nailing on more layers of plywood atop existing roof shingles - which would result in a reduced roof life and in most jurisdictions a code violation

On 2016-07-20 - by Anon

Re-posting from private email, writer kept anonymous:

Typically, how much does a sheet of 4x8 5/8” FRT Plywood cost?

Reply by (mod) -

Anon: the cost of a single sheet of FRT-treated plywood depends on the thickness required and other properties such as facing type, but you can figure typically around $19. U.S.D. / 1 4x8 foot sheet for quantities under 1000 sheets at the low end to as much as $35.00 for a single 1/2" (15/32") CDX FRT-treated plywood at a building supplier such as Menards.

Question: is FRT Plywood "Safe"?

I have a townhouse that still has FRT plywood. Is it safe? The th was built in 1985 - (Oct 20, 2012) Bill

I was told that a newer TH with OSB roof sheathing and no FRS plywood was OK because a sprinkler system is installed in the house. Sprinklers are not in the attic. Is this ok? - (Dec 24, 2012) Jeremy

Trying to educate my real estate due diligence staff on problematic fire retardant plywood. Need attic pictures showing the use and deterioration of the product. Can you direct me toward some pictures? - (Apr 24, 2014) Eric Bates

Reply: FRT plywood that's delaminated isn't safe

On a re-roof job one of our workers fell right throught the roof when walking over a section of delaminated FRT plywood - so clearly that's unsafe even apart from questions of its loss of fire resistance.

Eric, I've added another photo of the identifying stamp found on FRT plywood as it might be visible in an attic. Other photos of where the FRT plywood is likely to appear are shown in the article above.

Clicking on any of our images will present an enlarged, sharp-focused copy.

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Reader Question: when were building fire walls first required in homes?

My house was built with no wall separation ( firewall) in the attic! When did the Victorians start to use them? The sash windows upstairs has two bars up and down making six panes of glass in all but four downstairs!

Chimney pots are yellow with one bar top and bottom. I would be much grateful for any help dating the house! - A.C. 6/29/14

Reply:

Firewalls are a modern building safety feature used in multiple occupancy dwellings.
E.g. see historical citations given in the references on this page.

A victorian home built 100 years or more ago will not have used FRT plywood in its original construction.

Watch out: however if the roof was re-decked or re-framed between the 1960s and late 1980s you can't rule out the use of FRT plywood without first inspecting the roof decking and framing.

...

Continue reading at FIRE RATINGS for ROOF SURFACES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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Suggested citation for this web page

FIRE RETARDANT PLYWOOD at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING FIRE SAFETY

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING STRUCTURES

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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