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Curling wood shingle roof (C) Daniel FriedmanWood Shingle & Wood Shake Roof Fire Ratings
Can Coatings or Component System Increase Wood Roof Fire Rating From Class B or C to Class A?

Coatings for wood shingles or wood shake roofs - wood roof preservatives, wood roof fire resistive coatings:

This article explains fire resistant treatments and preservative treatments for wood shingle or wood shake roofing in historic and contemporary use.

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Class A Wood Shake or Shingle Roofs

Building fire Red Hook New York (C) Daniel Friedman at InspectApedia.comHow to Convert a Class-C to B or Class B wood shingle roof to Class A Fire Rating

Watch out: without more-complete information, don't assume that your roof has been properly classified & approved as Class-A fire rated.

Class A fire-rated wood shingle or shake roofs are can be achieved through a component roofing system, so no individual shakes or shingles can achieve a Class A rating. The components involve FRT treated wood shakes or shingles, a Class A cap sheet, and (probably) a layer of fire-resistant gypsum board over the wood deck (possibly also requiring FRT plywood decking)

Photo: building damaged by fire in Redhook, New York. [This was not a wildfire event but illustrates the catastrophic destruction of a building fire including the building's roof - Ed.]

[Click to enlarge any image]

Class A Cap Sheet + Panelized Fireproof Sheathing Under Wood Shakes or Shingles

Wood shakes or shingles that have been treated wth a fire-retardant chemical (FRT) can meet a Class-B fire rating, and these roofs can achieve a Class A fire rating if additional materials such as FRT plywood base and a Class A cap sheet, Type 72 roll roofing and panelized gypsum-fiberglass system such as DensDeck are installed.

In sum, Class B shakes or shingles can form part of a Class-A Fire Rate roof provided they aer installed over sheathing (spaced or solid) that in turn has been covered with one layer of 1/4 in. (6.4 mm) thick noncombustible roof board, or with one layer of minimum 72-lb. fiber-glass-based mineral surfaced cap sheet, or with another, equivalent and fire-rated specialty roofing sheet product in order to obtain the Class A fire rating.

Watch out: do not go ahead and try to build your class roof using wood shingles or shakes interpretation before checking with your local building code and fire officials: local codes and roof structures that are permitted vary by jurisdiction. In some jurisdictions where wildfires are a concern wood shingle or shake roofs may not be permitted, period.

Research on Construction of a Component-system Class A Wood Shingle or Shake Roof

Protective Coatings & Treatments for Fire Rating for Wood Shingle & Wood Shake Roofs - Getting from No-Rating to B-Rating to Class A Fire Rating

US FPL climate index for the US

Types of Wood Shingle/Shake Roof Treatments Available

As we mention in our outline of roofing materials and their properties found at ROOFING INSPECTION & REPAIR, wood shingle roofs, if treated with a fire retardant, are fire rated B.

Un-treated wood roof shingles have no fire rating and are not permitted by code in some areas. A class A fire rated wood shingle roof can be installed using special procedures and materials that include plywood and gypsum board.

NRCA's David Flickinger explained in 1999 in Professional Roofing, that treatments are available for wood shingles and wood shakes on building roofs to preserve the wood from rot and to increase its fire resistance. For new wood shingles, a pressure treatment impregnates the shingles with a wood preservative (in the 1990's CCA or chromated copper arsenate) or a fire retardant.

[Click to enlarge any image]

When shingles are treated with a fire retardant they are then heated to complete that treatment procedure.

Typical spray or brush-on wood roof treatments are also available to treat wood shingles or shakes that have already been installed on a building.

According to Flickinger, the Cedar Shake & Shingle Bureau (CSSB) recommends that cedar roofing products used in locations with high decay potential should be treated with a preservative.

A U.S. map provided by the Forest Products Laboratory (above-left) indicates that the southeastern quadrant of the U.S., but extending north into West Virgina and parts of eastern Kentucky and Tennessee make up this area of high decay hazard (the dark colored area on the map) based on the FPL climate index.

Questions About the Durability of Fire Retardants & Preservatives for Wood Roofs

According to the NRCA both of the wood roof processes described above, when wood roofing shingles or shakes are treated under pressure, before installation on the roof, are considered "permanent", that is, the treatment should last for the life of the wood shingle.

For existing wood shingle roofs, treatment might be applied using a topical spray or brush-on of preservatives. These treatments are not permanent and need to be performed periodically depending on the geographic locale of the roof

According to Best Practices Guide to Residential Construction (Steve Bliss, J Wiley & Sons) and discussed in BEST ROOFING PRACTICES,

Where premium red or white cedar is too expensive for a particular roofing job, wood roof buyers should consider pressure-treated southern yellow pine shakes and shingles. In its favor, yellow pine is a tougher and stronger wood, and although not as pretty as red cedar when new, over time they will both weather to a similar silver gray.

Because penetration of the treatment on pine roofing shingles is nearly 100%, pressure-treated pine shingles carry guarantees against decay for up to 50 years, making them well suited to high-moisture environments, shallow slopes, and shady wooded sites where organic matter may collect on the roof. The preservatives should not leach out over time.

One drawback to yellow pine shingles and shakes is that many are flat-grained, so most come pretreated with a water repellent to help them resist cupping and splitting. However, retreatment with a water repellent at some point may be required for optimal performance. Western red cedar shingles are also available pressure-treated for severe applications where standard cedar shingles are prone to decay.

A bit before Flickinger's 1999 article, in 1995 in his article on Choosing Roofing, Jefferson Kolle questioned the durability of wood shingle fire retardant treatments. Kolle suggested that rain tends to draw the fire retardant to the shingle surface where it is washed away over time.

The same article however, quoted Don Meucci from the Cedar Single & Shake Bureau who said that tests performed on fire-retardant-treated wood shingles from a 16-year old roof passed the current fire resistance tests of that time. Nonetheless, some communities where fire risk is particularly high (Los Angeles California, Newcastle, New Hampshire) have banned the use of wood roofs regardless of their treatment.

For added details about proper wood shingle or wood shake roof installation, perhaps the most authoritative source of wood shingle and wood shake information is from the Western Red Cedar Shingle & Shake Bureau (now the Cedar and Shake Shingle Bureau, since not only western red cedar is used for roof shingles).

Research on Use of Fire-Retardant Paint & Paint Sources to Protect Buildings

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-08-08 - by (mod) -

fire-retardant wood roof coating

Re-posting pending approval of included links:

Sean Harrison said:

A new, innovative, 100% eco-friendly wood coating that is shocking the world: once impregnated, your wood is protected for over 50 years, it is fire retardant, preventing bending, mold, worms, termites, UV damage and most important, water damage.

info@pd-18usa.com

On 2016-05-08 - by (mod) -

Sandra:

Yes there are spray-on fire retardant treastments for wood shingle roofs. I can't say what you need to do on a new roof, as some shingles may already have had fire retardant pre-applied. Some wood shingle roof products are pressure-treated with fire retardant when they are manufactured. That would probably be more effective than a spray-on retardant. What you should look at closely are the manufacturer's information about how long the fire retardant treatment lasts and when re-treatment is recommended.

According to x,
"Class B or C fire resistance ratings can be achieved for pressure treated wood shakes and shingles depending upon the amount of chemicals injected and/or the type of roof deck and underlayment used. "

- Smith Edwin G., et als, "The Wood Shake and Shingle Roof Hazard", University of Nevada Cooperative Extension, Fact Sheet 94-26, University of Nevada at Reno [PDF]

On 2016-05-07 by sandra

can you buy a fire treatment to put on an existing cedar shingle roof do new roofs have to be fire treated

Question: how to see if wood shingles are fire resistant

(Mar 25, 2012) Ona Hester said:
I need to know how to see if wood shingles are fire resistant

Reply:

Ona, if you do not have a record of who installed the roof, what product was used, nor a copy of documents describing the product, what's left is to send a sample to a shingle testing lab, asking for the appropriate ASTM test to be performed. The code requirement for treated shingles varies by geographic area, so you might start there.

Question: Is there a wood shingle treatment that provides both fire retardant and preservative?

(July 20, 2012) Bill Schubert said:
Is there a wood shingle treatment that provides both fire retardant and preservative?

Reply:

Bill, thanks, you ask an important question.

Wood shingle fire retardants (e.g. see FireRetardantsinc [dot] com Tel: 800-913-9385) are expected to be applied over new, un-treated wood shingles or shakes, and to be re-applied every few years to preserve their protection. I infer that if someone has already treated a wood roof with a preservative that imparts any water resistance to the wood shingle surface, the fire retardant treatment won't be effective as it won't soak into the wood as expected.

I pose that the fire retardant is also preservative, but I agree that the chemistry will vary. I've asked the experts to take a look at this Q&A and to comment further

Question:

(Oct 22, 2014) Joel said:
I have a 35 year-old wood shake roof, which was put over a now 55 year-old wood shingle roof.

Is there any (liquid) waterproofing material that can be sprayed (or brushed) over the outer wood-shake roof, to make it more leak proof? Is there any other way to make this roof more leak-resistent? (How the roof "looks" after this additional waterproofing is done is not important. I am located in Southern California.

Reply:

There are companies selling elastomeric roof coatings purporting to seal roof leaks. I would not attempt that repair on a wood shingle roof without discussing the process with the coating manufacturer.


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