Western Red Cedar Shakes and Shingles: A Sustainable, Versatile Roofing Choice  

When the insurance industry asked the roofing industry to test product resistance to hail damage, the steel ball drop UL-2218 impact resistance test placed CSSB member cedar shakes and shingle products at the top of the scale with Class 3 and Class 4 results.

UL-2218 is the Underwriters Laboratories test standard for Impact Resistance of Prepared Roof Covering Materials. The acceptance criteria upon examination after being subjected to the test procedure is: prepared roof covering material exposed surface, back surface and underneath layers shall show no evidence of tearing, fracturing, cracking, splitting, rupture or other evidence of opening of the prepared roof covering layer. For further information on this testing procedure please visit www.ul.com. The classifications for impact resistance are expressed as Class 1, 2, 3 or 4 which relate to a roof covering's ability to withstand impacts from 1 1/4, 1 1/2, 1 3/4 and 2" diameter steel balls, respectively. CSSB member products are available with a Class 3 or 4 impact resistance rating, depending upon product type. Some insurance companies in hailstorm prone areas will offer discounts on premiums if an impact resistance rated roofing material is used.

Cedar products are highly resilient in earthquakes, and are lightweight with no re-decking required, as with other heavier roofing materials. As a natural material, there are no artificial layers that can delaminate in freeze-thaw cycles. Since cedar naturally weathers to an attractive gray color, matching factory color lots if repairs are needed is not a concern.

Workmanship Issues

As with all construction materials, good workmanship practices that comply with local building codes are important design and construction issues. It should be noted that shake and shingle applications are not the same.

Basic application criteria include the following:

• Never interlay shingles with felt. Consult local building codes.


• Be sure that interlay felt on shakes does not extend below a line that is twice the exposure above the butt (i.e., a 24-inch shake at 10-inch exposure would have felt applied 20 inches above the butt)


• Keyways must not be aligned and must be a minimum 1 1/2" offset from the course above. Keyways are the spaces between adjacent shakes or shingles.


• Overdriving or underdriving the fasteners can seriously damage the integrity of the roof or wall system


• Only use stainless steel (type 304 or 316) hot-dipped zinc coated, or aluminum nails or other fasteners as accepted by the local building official. Always check with the pressure impregnation treatment company for the types of fasteners required for its products.


• Ring shank nails provide significantly higher wind uplift resistance

Both reduced exposure and staggered butt applications can result in additional product quantity requirements. A staggered butt design is achieved by shortening the exposure to less than the greater maximum exposure, not by overexposing some of the product or mixing product types. A staggered butt or a reduced exposure application can easily result in additional material costs, if appropriate calculations are not performed regarding the number of squares required for the project.

Historic Restoration and Renovation

Cedar shakes and shingles are often used on historic restoration and renovation projects, and can be made to resemble original materials. Examples of historically accurate products include tapersplit shakes that are produced by hand, using a sharp bladed steel froe and a mallet; and straight-split shakes, that are produced by machine or in the same manner as tapersplit shakes.

When working with historic replications, design professionals should keep in mind that materials should be selected that are specific to the period, not necessarily to the building's completion date. Design criteria for historic renovations with cedar shakes and shingles include the following:

• Avoid handsplit and resawn products. Handsplit shake machines were not available until approximately 1935.


• Shingle machines have been in existence since about 1835, developed by Shakers in Maine and New Hampshire.


• Shingle and shake application should be three ply buildup without felt paper.


• Use nailing strips, not solid deck sheathing.


• Antique sheathing boards were rough sawn, which leads to an uneven decking surface. Plywood and oriented strand board (OSB) panels are not authentic.


• Ridge airflow products are not historically accurate.


• Use hand nailing rather than any kind of power fasteners. Do not use staples.

A Renewable Resource

Wood is biodegradable, recyclable, renewable, and an environmentally sound building material. According to the American Forest and Paper Association (www.afandpa.org), "In 1999, the forestry community planted some 1.7 billion trees in the United States. That's an average of more than 4 million trees planted every day − more than 5 new trees a year for every man, woman and child in America."

There has been a concerted effort by government, industry, environmentalists, and other stakeholders over the last 20 years to develop a stringent set of forest management practices in the United States and Canada. Among all the building products available, wood is one of the few building products that is derived from a renewable resource.

Steel, aluminum, plastic and concrete are sometimes viewed as wood substitutes. The forest industry replaces what it removes; the same cannot be said about iron ore, bauxite, precious oil reserves, petroleum, or limestone materials.

Extending the Life of a Cedar Roof

Cedar has been proven to last over hundreds of years. The life of a cedar roof depends on various factors, including the quality of the product. Quality shakes and shingles are generally manufactured by mills subscribing to a third party inspection agency program. The grade of the product on the label is also important. Premium Grade shakes or Number One grade shingles are 100 percent edge (vertical) grain and will yield the longest life.

Installation should be performed by an experienced, quality-oriented roofing contractor. Subcontracting to crews is an acceptable industry practice, but architectural specifications should list required qualifications for subcontractors, including that they should be experienced, trained professionals.

Maintenance

The environment surrounding the structure is an important element for maintenance and roofing longevity. If there are overhanging trees near the roof, the branches should be pruned back regularly, or frequent maintenance will be needed by a qualified person to sweep the roof clear of debris.

Cedar needs to breathe, and allowing leaves, pine needles and other materials to build up on the roof is not advised. Sealants and debris both lock in moisture that would otherwise naturally evaporate during normal weather conditions.

The roof should be properly ventilated using a guideline of total net free ventilation area to the area of the attic should be not less than 1:150 or 1:300 if split equally between the attic and the eave. Gutters and downspouts need to be kept clean in order to prevent clogging. A downspout should not be allowed to drain directly onto a roof surface below. Instead, the flow of water should be directed away from the building.

The life of a cedar roof depends upon the amount of maintenance performed. All roofing materials need periodic maintenance checks and repairs. Cedar roof maintenance should be performed by professional inspectors familiar with safety precautions, generally at least twice a year, or after major storms, so that any damage can be repaired or built up debris removed.

Typically, the ridge cap used at peaks and hips (where two sloping sides of the roof meet at areas which are not the apex of the structure) on a roof will require replacement first, as this area takes the brunt of any weather system affecting the structure. The roof should also be checked for loose fasteners, split product where felt is exposed, or damage from hailstorms. With proper preventative maintenance and installation of quality materials, a heavy handsplit and resawn cedar roof can last 50 years or more. Identifying the difference in naturally weathered and storm damaged cedar roofs is sometimes a difficult task. It takes a trained eye to assess a cedar roof and determine if it is in fact damaged due to hail, or if it is just naturally weathered. It also takes a trained eye to determine the amount of repair required. Use appropriate repair versus replacement methodology (contact the CSSB for more details).

Another benefit to using cedar shakes and shingles is that repairs can be made readily only to those roof sections that need it, rather than tearing off the entire roof after storm damage.

If an enhanced lifespan is of critical importance, then using a pressure impregnated preservative treated cedar shake or shingle product should be considered. Another option is to nail zinc or copper strips at the ridge for moss control. However, for some roofs, this method is only effective for a few courses underneath the metal strip and this alone should not be considered sufficient to complete the maintenance program. Use of a bleach and water solution to clean surface debris and halt the growth of lichens and moss is another option. The United States Department of Agriculture (USDA) Forest Product Laboratory in Madison, Wisconsin is an excellent source of information. (www.fpl.fs.fed.us/)

Pressure or Power Washing

Pressure or power washing in the roofing industry refers to a machine-driven, high velocity stream of water being directed at the surface below, conducted from the water source via a wand held by a human operator.

When weighing the benefits and drawbacks of using pressure washer machines on a cedar roof, several factors should be considered, including the experience of the person performing the work, the age and condition of the roof, the pressure per square inch, spray tip, distance from the roof, and washing technique. Pressure washing equipment, when placed in the hands of an inexperienced person, can cause significant damage to a roof. When used properly, pressure washers can be effective in removing surface debris. It is critical to clean from the top down, using proper technique, in order not to blow water up into the attic area. An inspection of the roof first should be performed to note any shakes or shingles in need of replacement.

Topical sprays can be considered for preservative reasons. These sprays are not a replacement for the pressure impregnation treatment that is available from the factory prior to the roof being installed. Design professionals who wish to use a topical treatment product on an untreated roof should be aware of several important guidelines.

Do use a topical treatment product that:

• Offers a Material Safety Data Sheet (MSDS), that lists product ingredients and safety precautions


• Is labeled as a cedar roof treatment product or has a letter from the manufacturer stating that treating cedar roofs is an appropriate use for this product


• Is a water repellent, ultraviolet (UV) inhibitor, and/or U.S. Environmental Protection Agency (EPA) registered wood preservative


• Has a manufacturer's performance guarantee

Do not use a topical treatment product that:

• Makes outrageous claims (such as a 10-year effectiveness)


• Makes fire retardant claims


• Is a sealant, waterproofer or plasticizer


• Contains unfortified linseed oil, diesel fuel or crank case oil

Before considering any treatment or cleaning solution application to a pressure impregnated treated roof, always check with the pressure impregnation treatment company to see if it will affect the treatment warranty.

Industry reference guides include the "New Roof Construction Manual" and "Exterior and Interior Wall Manual," available for free from the CSSB.

Lynne Christensen, MBA, CAE, is the Director of Operations for the Cedar Shake and Shingle Bureau. Ms. Christensen has worked in the roofing industry for 15 years and was a team member deployed to the Hurricane Katrina area to assist the insurance industry with structural damage assessment. She can be reached at lynne@cedarbureau.com.

Glossary Terms

• Bundle strap: Metal or plastic band used to hold a bundle of shakes or shingles together


• Extractive bleeding: Extractive bleeding (stains) on the surface of Western Red Cedar occur when extractives are dissolved and leached from the Western Red Cedar by water. The water then moves to the finished/coated surface, evaporates and leaves the extractive discoloration which may be dark red or reddish-brown in appearance. Extractive bleeding is easily prevented when the proper primer and topcoats are applied using the coating manufacturer's recommended spread rates, time of application (i.e., not too cold/hot or in direct sunlight). Environment and moisture content level should be considered during the application phase.


• Fivex: A shingle of 16" nominal length


• Froe: Sharp metal blade with handle used in conjunction with mallet to split shakes by hand


• Keyway: Space between adjacent shakes or shingles


• Mallet: Hammer-like tool used in conjunction with froe to split shakes by hand


• Material Safety Data Sheet: Product document containing items such as precautions, product composition, emergency response procedures and operating instructions. Provided to handlers, sellers, users and other parties associated with said product to ensure health, safety and proper work procedures.


• Pallet strapping: Metal band used to hold multiple bundles of shake or shingle products together on pallet


• Perfection: A shingle of 18" nominal length


• Photodegradation is the chemical transformation of a compound into smaller compounds caused by the absorption of ultraviolet, visible, or infrared radiation (light). (This definition is taken from http://toxics.usgs.gov/definitions/photodegradation.html and International Union of Pure And Applied Chemistry (IUPAC), 1996, Glossary of terms used in photochemistry (IUPAC Recommendations 1996): Pure and Applied Chemistry, v. 68, no.12, p. 2223-2286.)


• Pressure impregnated fire retardant treatment: Permanent fire protection is provided by factory pressure-impregnating fire retardant polymers into the innermost cells of shakes and shingles to meet Class A, B and C testing standards.


• Pressure impregnated preservative treatment: Long term protection from fungal decay is provided with factory pressure-impregnated treatment of preservatives that will extend the life of cedar shake and shingle roofs.


• Rebutted and Rejointed (R&R) sidewall shingles: A sawn shingle, remanufactured on four sides to ensure square butts and parallel edges for superior appearance on sidewall applications. Also available with sanded or machine grooved face. Predominately kiln dried. Pre-primed or pre-stained options available.


• Ridge (hip and ridge) material: Two shakes or shingles preassembled into units that cap the peaks or hips of a roof structure
• Royal: A shingle of 24" nominal length


• Shake: There are two main types: (1) handsplit and resawn and (2) tapersawn. Handsplit and resawn shakes have the split face exposed with a naturally rustic appearance, and are sawn on the back. Tapersawn shakes are sawn on both sides for a semi-textured look with a stronger shadowline than a shingle.


• Shingle: A shingle is sawn on both sides for a tailored appearance with a less strong shadowline than a tapersawn shake. Shingles are available in 16" Fivex, 18" Perfection or 24" Royal nominal lengths.


• Square: Amount of material required to cover 100 square feet

www.cedarbureau.org The Cedar Shake and Shingle Bureau (CSSB) was founded in 1915 and is the industry's trade association representing over 300 members. It offers AIA continuing education seminars, free technical advice and literature, as well as field representation.