Cedar Shakes and Shingles

Cedar Shakes and Shingles

1. General Product Information

1.1 Product Type
1.2 Roofing Categories
1.3 Product Manufacturers
1.4 Manufacturing Process
1.5 Industry-Specific Standards, Codes Requirements, and Compliance

1.1 Product Type

1.1.1 Shake and Shingle Descriptions

The following definitions are only intended to provide a brief overview of the differences between basic product types. For more information on installation, product spacing, fasteners, and grading, please contact the Cedar Shake & Shingle Bureau (CSSB). For full information, please view the product catalog at www.cedarbureau.org/pdf2013/Specsheet-low-res-03-27-13.pdf.

Certi-Split® Handsplit and Resawn Shake:

  • Split face exposed with a naturally rustic appearance, sawn on back
  • Most common are 18 inch and 24 inch lengths
  • Butt thickness ranges from 3/8 inch to 1 inch plus (Note: Jumbo resawn shakes have a minimum butt thickness of 1 inch)

Certigrade® Shingle:

  • Sawn on both sides for a tailored appearance
  • Available in 16 inch (Fivex), 18 inch (Perfection) or 24 inch (Royal) lengths
  • Butt thickness is gauged using a stack of shingles to meet the proper measurement

Certi-Sawn® Tapersawn Shake:

  • Sawn on both sides for a semi-textured look with a stronger (pronounced) shadowline than a shingle
  • Most common are 18 inch and 24 inch lengths
  • Butt thickness ranges from 5/8 inch to 1½ inches

www.cedarbureau.org/cms-assets/documents/26244-377055.difference-between.pdf

Figure CEDAR-1-1 describes differences in product quality using a grading system developed by CSSB and used to certify products produced by their members.

Figure CEDAR-1-1. Cedar Shake & Shingle Bureau product Types and Grades.

Figure CEDAR-1-1. Cedar Shake & Shingle Bureau product Types and Grades.

1.1.1.1 Product Ingredients

Shakes and shingles are made from either Western Red Cedar or Alaskan Yellow Cedar. Much of the wood fiber utilized is from salvage wood, or wood that would otherwise be left on the forest floor, thus making these products very environmentally friendly. Treated products use either a pressure-impregnated fire-retardant treatment or a preservative treatment, but not both. A post-treatment process helps fix the chemical in the wood.

1.1.1.2 Product Quality

The quality of the installed shakes or shingles will largely determine the longevity of a cedar roof. The highest quality shakes and shingles are 100% edge grain Western Red Cedar or Alaskan Yellow Cedar and are free of knots and other growth defects and do not include sapwood. Lower-quality shakes and shingles will include varying amounts of flat grain, sapwood and knots.

Figure CEDAR-1-2. Flat Grain and Edge Grain Product Examples

Figure CEDAR-1-2. Flat Grain and Edge Grain Product Examples

Figure CEDAR-1-2 illustrates the differences between flat grain and edge grain products. These differences can be easily identified by looking at the exposed surfaces and butts of shakes and shingles. No flat grain is allowed in Premium Grade cedar shakes or Number 1 Grade cedar shingles. Premium Grade shakes are the top shake grade, whereas Number 1 Grade shingles are the top shingle grade.

Number 1 Grade shakes are allowed to have up to 20% flat grain per bundle. Knots, flat grain, sapwood and other defects in the exposed portion of the shake or shingle are a clear indication of lower quality.

Coverage refers to the amount of on grade lineal inches in a bundle of roofing material (or a carton of sidewall material). Lower quality or “off-grade” products will not provide sufficient coverage without increasing order quantity. An example demonstrating “coverage” is shown in Figure CEDAR-1-3.

Figure CEDAR-1-3. Examples of good- and low-coverage quantities.

Figure CEDAR-1-3. Examples of good- and low-coverage quantities.

Traceability is determined by the product label affixed to each bundle of shakes or shingles. This is where one finds the manufacturer and inspection agency information. Information on how to read a Certi-label™ is provided at www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p25.pdf.

1.1.2 Packaging

Figure CEDAR-1-4. Example labels for CSSB member products which are treated.

Figure CEDAR-1-4. Example labels for CSSB member products which are treated.

Pressure-impregnated treated products, either fire-retardant treated or preservative treated, will have a treatment label, such as one of those shown in Figure CEDAR-1-4. If the product is already installed and the label is not available, it will not be possible to determine whether the product has been treated without sampling and analyzing at an analytical laboratory. In these cases, it should be assumed that the product has not been treated.

1.2 Roofing Categories

The minimum roof slope on which Certi-label™ shakes are recommended is 4:12, and for Certi-label™ shingles, 3:12. It is typical to see installations with slopes greater than these. (IRC and IBC codes allow a minimum roof slope of 3:12 for shakes and shingles.)

Mansard roofs installation guidelines are found here:
www.cedarbureau.org/installation-and-maintenance/roof-manual/page-06.asp

Low-slope roof installation guidelines are found here:
www.cedarbureau.org/installation-and-maintenance/roof-manual/page-07.asp

1.3 Product Manufacturers

Additional information about cedar shakes and shingles as well as links to manufacturers are available from CSSB at www.cedarbureau.org or by emailing info@cedarbureau.com.

1.4 Manufacturing Process

Cedar shakes and shingles have been manufactured for over 100 years, and not much has changed in the manufacturing process during this time, which is one of the fascinating things about this natural roofing product. The first step in creating cedar shakes or shingles is to convert logs into round blocks. Bark, knots, and checks are removed from the blocks by cutting and/or sorting.

1.4.1 Cedar Shakes

When using logs, a boom of logs is towed to the river’s edge. Each log is guided into the mill and a saw cuts the logs into appropriate lengths called “rounds.” Each round is cut into wedges following the grain of the natural fiber. Material can also be cut into round blocks in the forest harvest area.

The wedges or blocks are then made into “blanks” of the proper cut area and width to feed into the automatic shake machine. The blanks are guided through the bandsaw of the automatic shake machine by metal fingers and rubberized rollers, and are sawn into two handsplit and resawn shakes. The two shakes tumble into the chute below to be graded and bundled for shipment.

1.4.2 Cedar Shingles

Blocks move up a conveyor and are placed on a table for the sawyer. A “shingle weaver” is an employee who operates two saws, one to cut shingles and one called a jointer saw stationed in from of the sawyer used to trim the edges of the shingles. After being formed, the shingles are packed by stacking in bundles, which are compressed so the bandstick and metal strap can be securely nailed.

1.4.3 Weathering of New Product When Used as a Replacement Material

Replacement sections and individual shakes or shingles will weather naturally to the same general gray color as the rest of the roof within six to nine months, on average. An example of this is provided in Figures CEDAR-1-5 and CEDAR-1-6, which show the same roof in its unweathered (Figure CEDAR-1-5) and weathered (Figure CEDAR-1-6) state about nine months later. The weathering process is affected by the time of year the replacement occurs and the surrounding environment, thus an exact timeframe cannot be provided.

Figure CEDAR-1-5. An unweathered cedar shingle roof.

Figure CEDAR-1-5. An unweathered cedar shingle roof.

Figure CEDAR-1-6. The same shingle roof as shown in CEDAR-1-5. A natural gray color was achieved after about nine months of natural weathering.

Figure CEDAR-1-6. The same shingle roof as shown in Figure CEDAR-1-5. A natural gray color was achieved after about nine months of natural weathering.

1.5 Industry-Specific Standards, Codes Requirements, and Compliance

1.5.1 Impact Resistance—Hail

Impact resistance can be evaluated using a standard test method outlined in UL 2218, as previously described in Chapter 3. Some CSSB member Certi-label™ shakes and shingles have withstood the impacts of up to 2-inch-diameter steel balls dropped from a 20-foot height, as per the UL 2218 test standard. Products having a Class 3 or 4 designation are available, and Class 4 is the highest impact resistance rating. Contact the specific manufacturer for details on product offerings. The impact resistance ratings in the UL 2218 test standard are the same for all products, regardless of product type. Thus, a Class 4 roof covering is the same, whether discussing cedar, asphalt, metal, or any other roofing material. For cedar roofs exhibiting hail damage, it is relatively simple to replace individual shakes or shingles. Because of the previously mentioned color change as a result of natural weathering, color matching is not necessary.

Caution: Not all cedar products are alike. Compliance with a test standard such as UL 2218 will be labeled.

1.5.2 Wind Resistance—Shake or Shingle Uplift

The uplift resistance of cedar shakes and shingles from wind is evaluated using UL 1897. In 2004, shakes and shingles provided by CSSB members were tested according to this standard test method (fourth edition), with results of 90 psf (190 mph) for CSSB member shakes and shingles. Additional testing by Exterior Research & Design, LLC showed results of 173 mph for CSSB shingles and 245 mph for CSSB shakes. A subsequent report by a Florida Registered Professional Engineer converted results, using no safety factors. Extrapolation calculations were performed for a specific house in the Miami-Dade County area of Florida using the analytical method for wind design of roof cladding set forth in Section 6 of ASCE-7-98 (American Society of Civil Engineers). For a full engineer’s report, contact the CSSB.

CSSB member Certi-label™ products have met stringent Miami-Dade County, Florida requirements. Miami-Dade County, Florida, is considered to have the toughest wind resistance regulations in all of North America and roofing products are evaluated using TAS 100-95 Uplift Testing. Water is also added into this test’s wind stream to ensure the roof deck is free from leakage.

Caution: Not all cedar products are alike. Compliance with a test standard such as UL 1897 or TAS 100-95 will be labeled.

Note: The highest ratings for UL 1897 and TAS-100-95 standard test methods for CSSB member products were both achieved when installations used ring-shank nails.

For more information on cedar shake and shingle products and installation, see the following resources (note that the CSSB does not supersede building code):
www.cedarbureau.org/installation-and-maintenance/roof-manual
www.cedarbureau.org/cms-assets/documents/24826-485192.cssb-adjusters-guide-to-hail.pdf
or
www.cedarbureau.org/cms-assets/documents/23180-613565.weather-res-brochure.pdf

1.5.3 Fire

How long the roof over a building can ultimately resist the penetration of fire is an important performance property. Fire ratings for roof coverings include Class A, Class B, Class C and “unrated” (i.e., coverings that don’t meet Class C). These classes are the same for all roofing materials, including asphalt composition shingles, metal (aluminum and steel), and concrete tile.

The standard fire test, as specified by UL 790 (and ASTM E108, a similar test procedure) includes four parts, as indicated below, and a roof covering must meet the criteria established for each part in order to achieve a given fire rating (i.e., Class A, B, or C).

  1. Intermittent Flame Test
  2. Spread of Flame Test
  3. Burning Brand Test
  4. Flying Brand Test

Class A fire-rated roof coverings or roof assemblies provide the highest level of fire resistance, followed by Class B and C. Untreated shakes and shingles are unrated, meaning they do not meet the requirements for Class C. Class A coverings are required on commercial and residential buildings in many wildfire-prone areas where building codes have been adopted. A Class A rating is achieved through the use of a Class B fire-rated shake or shingle with additional underlying materials that enhance the fire-resistance of the roof assembly. Class B roofing systems are required for use on apartment buildings, condominiums and commercial buildings. If a cedar shake or shingle roof is allowed in wildfire-prone areas, it will be required to be Class A. Check with the jurisdiction having authority for details. Certi-label™ cedar shake and shingle roof coverings exist in all three classes, either by the shake or shingle itself, or through the use of an assembly in the case of a Class A fire rating.

If you live in an area where the risk of wildfire is high, CSSB member pressure-impregnated fire-retardant-treated cedar shakes and shingles provide an additional value-added component, proven in eight rigorous tests within the UL 790 test standard:

  1. Intermittent Flame Test without amended rain test
  2. Spread of Flame Test without amended rain test
  3. Burning Brand Test without amended rain test
  4. Flying Brand Test without amended rain test
  5. Intermittent Flame Test after amended rain test
  6. Burning Brand Test after amended rain test
  7. Flying Brand Test after amended rain test
  8. Natural Weathering Test (tests 1 and 3–7 are redone after natural weathering of 1, 2, 3, 5, and 10 years outside)

In lieu of an accelerated weathering procedure, California, in particular, requires fire-retardant-treated shakes and shingles to undergo natural weathering (i.e., weathering outside). Fire tests are then conducted after the first, second, third, fifth, and tenth year of weathering. The long-term weathering is intended to provide a better understanding of long-term performance over the anticipated service life of the shake or shingle when installed as a roof covering.

Caution: Not all cedar products are alike. Compliance with a test standard such as UL 790 or ASTM E108 will be labeled.

1.6 Unique Industry-Specific Flashing Details

Proper installation of flashing at roof valley and roof projections is critical. Installation details can be different for Certi-label™ shingles and shakes, so care must be taken to ensure proper installation. Flashing materials should be pre-painted on both sides using a good metal or bituminous paint.

Recommended roof valley flashing material and installation are found here:
www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p10.pdf.

Recommended roof projection flashing details are found here:
www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p11.pdf.

2. Installation Guidelines

2.1 Best Practices
2.2 Roof Sheathing Materials Options
2.3 Underlayment Options
2.4 Installation Methods
2.5 Accessory Items

2.1 Best Practices

Proper installations of cedar shakes and shingles have the following characteristics that should be visible without destructive evaluation (See Figure CEDAR-2-1):

  • Uniform spacing between shakes of 3/8 inch to 5/8 inch, or uniform spacing between shingles of 1/4 inch to 3/8 inch
  • Adjacent course joints offset a minimum of 1½ inches (Note: Shingles allow no more than 10% in direct alignment in alternate courses)
  • No exposed fasteners
  • No exposed interlaid felt (Note: Shingles do not utilize a felt interlayment)
  • Even courses
  • No overexposed product (on a staggered butt application, no shake or shingle should be exposed beyond its maximum allowable exposure length)
  • Adequate attic ventilation as required by code
Figure CEDAR-2-1. Examples of key elements to be checked during visual inspection.

Figure CEDAR-2-1. Examples of key elements to be checked during visual inspection.

Spaced sheathing supporting shakes should be 1 inch x 4 inch or 1 inch x 6 inch dimension lumber. Spaced sheathing supporting shingles should be 1 inch x 4 inch dimension lumber. Plywood strips are never recommended, as they may not meet the 1 inch x 4 inch dimensional requirements, and may become weak and break between trusses or rafters. The butt end of shakes or shingles should project 1½ inches beyond the fascia at the eave, and 1 inch beyond the rake edge at gable ends. Shakes should have a starter course of one or two layers of cedar shingles or shakes (double or triple layer, as seen from the butt end) at the eaves and the first (eave) course for shingles must be a double or triple layer. Metal flashing should be visible in valleys. The minimum extension requirement of flashing under the shakes or shingles should be noted (see www.cedarbureau.org/installation-and-maintenance/roof-manual/page-10.asp and www.cedarbureau.org/installation-and-maintenance/roof-manual/page-11.asp) at transitions in roof slope, at ridges and along intersections of the roof surface with any wall surface. Closed valleys (where metal is not visible) may be allowed by local building code, but are not recommended.

2.2 Roof Sheathing Materials Options

Shakes and shingles may be applied over spaced sheathing. Solid sheathing is recommended for shakes and may be required in seismic regions or under treated shakes and shingles. Solid sheathing is also used in areas with wind-driven snow. The only solid sheet sheathing that has been tested with Certi-label™ shakes and shingles is plywood, but manufacturers may allow application over OSB. Refer to your local building code or building official for requirements for sheathing thickness/dimensions/grade. Additional details and diagrams are available at www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p3.pdf.

2.3 Underlayment Options

The recommended permeable interlayment for use with cedar shakes and permeable underlayment for shingles is No. 30 ASTM D4869 Type IV or No. 30 ASTM D226 Type II. It is never recommended to interlay felt with shingles, and would be a violation of IRC and IBC code. (www.cedarbureau.org/installation-and-maintenance/roof-manual/page-04.asp)
It is recommended that shake installations include interlaying of felt between shakes starting two times the exposed length of the shake above the shake butt.
Do not cover the entire roof deck with non-permeable underlayment. Check local building code requirements for proper attachment of underlayment, especially in high-wind zones.

2.4 Installation Methods

2.4.1 Exposure Length

The length of the exposed portion of a cedar shake or shingle depends on the length and quality of the shake or shingle. Tables CEDAR-2-1 and CEDAR-2-2 provide general industry guidance on maximum exposure lengths for cedar shingles and shakes, respectively.

Table CEDAR-2-1. Maximum Recommended Exposure Lengths for Cedar Roof Shingles

Maximum Recommended Exposure Length (inches)
Slope/Length Number 1 Blue Label Number 2 Red Label Number 3 Black label
Shingle Length 16 18 24 16 18 24 16 18 24
3:12 to 4:12 Slope 4 3 5
4:12 Slope and Steeper 5 4 4

Table CEDAR-2-2. Maximum Recommended Exposure Lengths for Cedar Roof Shakes

Slope/Length Maximum Recommended Exposure Length (inches)
Shake Length 18 24
4:12 Slope and Steeper 10 (a)
24 inches x 3/8 inch handsplit shakes limited to 7½ inch maximum weather exposure per UBC and IBC

2.4.2 Fasteners

Use two fasteners per shake or shingle as follows:

Stainless steel Type 316 fasteners are required for cedar shakes or shingles installed within 15 miles of salt water. In areas outside the salt water zone, Type 304 stainless steel, Type 316 stainless steel or hot-dipped galvanized (with a coating weight of ASTM A153 Class D – 1.0 oz/ft2) fasteners are allowed (see www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p12.pdf).

Stainless steel Type 316 fasteners are required for pressure-impregnated treated cedar shakes or shingles in all areas.
Reducing product exposure does not reduce the number of fasteners needed.

There are industry recommendations for size (i.e., gauge) and length of fasteners to be used depending on length and type of shingle or shake product being installed. Table CEDAR-2-3 provides industry guidance on fastener type (size) and length, depending on the type of shake or shingle being installed.

Table CEDAR-2-3. Industry Recommended Minimum Fasteners

Type of Shake or Shingle Length of Shake or Shingle (inches) Nail Type Minimum Nail Length (inches)
Straight-Split Shakes 18 5d Box
Handsplit and Resawn Shakes 18 and 24 6d Box 2
Tapersplit Shakes 24 5d Box
Tapersawn Shakes 18 and 24 6d Box 2
Shingles 16 and 18 3d Box
Shingles 24 4d Box

Non-galvanized and electro-galvanized fasteners should never be used with cedar shakes or shingles. If incorrect fasteners are used, loose shakes or shingles, uneven courses where shakes or shingles have slipped out of place, or even roofing product that has slid into the gutter or completely fallen off the roof may occur. Incorrect fastener placement can result in excessive cupping, curling, or lifting of the cedar shake or shingle. These types of deformations can cause the roof to leak. You should not be able to pull a correctly installed shake or shingle out from its course without using proper tools.

UL 1897 high-wind ratings for cedar shakes and shingles were achieved using ring shank nails and 1 inch x 4 inch wood battens. Similarly, Florida Building Code TAS 100-95 high-wind ratings including Miami-Dade County approvals were achieved using ring shank nails and solid plywood decking. Consequently, the use of smooth shank nails will lead to lower nail withdrawal capacities for the same size shank diameter, and rink shank nails would be best used in high-wind zones.

For additional installation guidance including illustrations of different installation and sheathing examples, see www.cedarbureau.org/installation-and-maintenance/roof-manual.

2.5 Accessory Items

Access www.cedarbureau.org/installation-and-maintenance for details regarding accessory products, ventilation, ridge, fasteners, ventilation, valleys, installation and more.

3. Repair and Maintenance Guidelines

3.1 Natural Aging Vs. Damage
3.2 Individual Shake or Shingle Repair or Replacement
3.3 Blending New and Old
3.4 Disposal/Recyclability of Products
3.5 Fastener Failure
3.6 Maintenance/Upkeep Guidelines
3.7 Expected Product Life Cycle

3.1 Natural Aging Vs. Damage

The useful service life of a cedar shake or shingle roof will vary depending on many factors, including: local environmental conditions where it is installed, wood quality, quality of installation, care and maintenance performed, foot traffic, and amount of overhanging trees. See details regarding treatments, care, and maintenance at www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr201.pdf.

Proper age assessment takes into consideration any of the following items: surface growth of mold, algae, or moss; leaf/pine needle buildup; moisture content; and surface butt/erosion. Some eventual curling, cupping and splitting on a cedar roof is normal, since cedar is a naturally durable material. Due to 100% vertical grain content, Premium Grade shakes and Number One Grade shingles do not have as much dimensional change as lower grades that allow some flat grain (see Figure CEDAR-1-1 for description of grain structure). Excessive cupping and curling is usually due to improperly placed nails, e.g., too far away from the butt end or too far from the edge; improper installation of the ventilation system between the sheathing system and the shakes and/or shingles; non-permeable underlayment installed over entire sheathing system utilizing an inadequate ventilation system between the non-permeable underlayment and the shakes and/or shingles; or due to lower-grade product. If it is determined that the excessive cupping and/or curling will affect the integrity of the roofing system, repair or replacement is necessary. Section 2.2 (Installation Guidelines) provides illustrations and steps that are typically taken in the repair of a cedar roof.

Changes in color occur over time, changing from Western Red Cedar’s natural reddish brown or Alaskan Yellow Cedar’s yellow coloring to a silver or dark gray.

3.2 Individual Shake or Shingle Repair or Replacement

Figure 3-1. Tools typically used to replace a cedar shake or shingle.

Figure 3-1. Tools typically used to replace a cedar shake or shingle.

Cedar shake or shingle roofs can be repaired and the newly installed product will weather to the same color as surrounding materials within six to nine months (on average). Storm damage does not always mean a full roof replacement is necessary. In the aftermath of a storm, a phenomenon known as “neighboritis” (i.e., “My neighbor got a new roof, therefore I should get a new roof too.”) may lead to more roof replacements than are actually needed, which results in increased costs, increased wait times for repairs, and increased materials being disposed of in landfills. Sometimes it is better to repair a roof rather than completely replace it, especially when considering a cedar roof section repair will blend in with the original roof in a relatively short time period. (Note: Appropriate analysis and information can be found at www.cedarbureau.org/cms-assets/documents/24826-485192.cssb-adjusters-guide-to-hail.pdf.) Figure 3.2-1 shows tools typically used in the repair and replacement of cedar shakes and shingles.

Figure 3-2. Steps involved in one typical method for cedar shake or shingle replacement.

Figure 3-2. Steps involved in one typical method for cedar shake or shingle replacement.

Figure 3-2 illustrates steps involved in one method for shake or shingle replacement. Shims can be used to repair an occasional split or defect from below, as shown in Figure 3-3. This is usually done when the split or defect is less than 1½ inches from the edge of the shingle below. The CSSB recommends that no more than 20% of a roof area be shimmed.

Figure 3-3. Illustration of shim installation to repair a split or defect.

Figure 3-3. Illustration of shim installation to repair a split or defect.

Additional guidance on repairs and replacement of shakes or shingles is available at www.cedarbureau.org/cms-assets/documents/45094-350971.cmbrochure2011.pdf or www.cedarbureau.org/cms-assets/documents/24826-485192.cssb-adjusters-guide-to-hail.pdf.

3.3 Blending New and Old

Because new cedar shakes and shingles will quickly weather to the same general gray color as the rest of the existing roof, as long as the same type of product is being used, the new and old pieces will blend together after about six to nine months, on average.

3.4 Disposal/Recyclability of Products

The cedar shake and shingle industry maximizes wood resources brought into manufacturing by using some salvaged wood fiber, or wood left over from past logging work or windblown material left on the forest floor. These materials are unsuitable for lumber mills, but can be used by cedar shake and shingle producers. Trees are a renewable resource so the use of wood building products is an environmentally sound choice. Wood is eminently recyclable and biodegradable.

3.5 Fastener Failure

A Licensed Roofing Consultant, or someone properly trained, should evaluate the issue to confirm widespread fastener failure. Fastener failure cannot be repaired; a tear-off and replacement of the shakes or shingles would, most likely, be the recommendation of the licensed independent assessor.

3.6 Maintenance/Upkeep Guidelines

CSSB offers information on the proper care and upkeep requirements for cedar roofs in its “Cedar Roof Care & Maintenance” guide available at www.cedarbureau.org/cms-assets/documents/45094-350971.cmbrochure2011.pdf. The reader of this document is urged to review this guide.
The USDA Forest Products Laboratory has a comprehensive publication (FPL-GTR-201) on wood roof maintenance at www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr201.pdf.

Some general guidelines include:

  • Trimming overhanging branches
  • Regularly cleaning downspouts and gutters
  • Removing leaves, branches, or other debris from the roof surface promptly
  • Ensuring ventilation is available year-round by keeping louvers and vents clear of debris

3.6.1 Powerwashing

Figure 3-4. Powerwashing damage.

Figure 3-4. Powerwashing damage.

High-pressure-washing by inexperienced people will cause significant damage to any material, such as that shown in Figure 3-4. Some debris can easily be removed with garden hose pressure. If powerwashing is used, the roof should receive a topical treatment to restore the roof. The Cedar Shake & Shingle Bureau recommends having a professional assess each job on an individual basis. More information can be found at www.cedarbureau.org/cms-assets/documents/45094-350971.cmbrochure2011.pdf.

3.6.2 Walking on Product

Figure 3-5. Footfall split damage (note no denting and new cedar color). Photo courtesy of Haag Engineering.

Figure 3-5. Footfall split damage (note no denting and new cedar color). Photo courtesy of Haag Engineering.

The less foot traffic on a cedar shake or shingle roof, the better, as foot traffic can cause damage such as that illustrated in Figure 3-5. Unless absolutely necessary for assessment or repair, walking on these roofs should be avoided.

3.7 Expected Product Life Cycle

The life expectancy of cedar shake or shingle roofs will vary depending on many factors, including: local environment where installed, wood quality, quality of installation, care and maintenance performed, foot traffic, and amount of overhanging trees. Proper age assessment takes into consideration any of the following items: surface growth/leaf/pine needle buildup, moisture content and surface butt/erosion.

4. Damage Issues

4.1 General Information
4.2 Identifying Damage
4.3 Determining Hail Damage
4.4 Determining Wind Damage
4.5 Determining Fire Damage
4.6 Determining Cold Weather Damage

4.1 General Information

4.1.1 Product Identification

The label under the bundle strap of cedar roofing materials should include a “Certi-label™” designation at the top. Options include “Certi-Split®,” “Certi-Sawn®” and “Certigrade®.” Ridge material is called “Certi-Ridge®.” An additional label indicating “Certi-Last®” preservative-treated material or “Certi-Guard®” fire-retardant-treated material may also be found on the bundle or pallet if those respective treatments have been impregnated into the shake or shingle. Other “Certi-label™” products exist for sidewall applications. A useful diagram detailing the different components of a shake or shingle label, including manufacturer, product type, product dimensions and applicable codes/standards that the product meets are provided at www.cedarbureau.org/installation-and-maintenance/roof-manual/page-25.asp.

To learn about the differences between a shake and a shingle, refer to Figure CEDAR-1-1.

4.1.2 Product Selection

Although good quality cedar shakes and shingles are readily available, there are suspect products in the marketplace. The Cedar Shake & Shingle Bureau provides an overview of how to choose the correct, quality-manufactured cedar roofing product at www.cedarbureau.org/cms-assets/documents/67060-723658.qcbrochure.pdf. Not all cedar shake and shingle products are the same.

All Cedar Shake & Shingle Bureau members are listed on the CSSB website: www.cedarbureau.org (look for the “Find a Member in Your Area” box at the bottom center of the page). Affiliate members include contractors, distributors, retailers, wholesalers and brokers. Homeowners and Claim Adjusters typically deal with contractors who will then purchase products from a member supplier. You can also contact member manufacturers directly (see www.cedarbureau.org/purchasing/manufacturers.asp) if you have questions about their specific product and/or limited warranty.
For product selection, refer to the product catalog at www.cedarbureau.org/pdf2013/Specsheet-low-res-03-27-13.pdf.

4.2 Identifying Damage

Thorough cedar roof inspections must be performed on the roof—these inspections cannot be conducted from the ground. All areas of the roof should be checked for possible damage, including fasteners and flashings. All of these elements work together to form the cedar roofing system. Note that normal wear and tear as a result of weathering will occur over time. Normal weathering does not include storm damage, and may consist of splitting, cupping and curling. Excessive amounts of these items could mean that a lower-quality material was used or that the material was improperly installed. Improper installation can include poor fastener placement. Pay particular attention to missing or dislodged fasteners, and underlayment exposed to the weather. Missing or dislodged fasteners can result in loose shakes or shingles. Excessive damage of any kind indicates that action is necessary.

The CSSB does not recommend new installations or retrofitting where a non-permeable membrane covers the entire roofing deck. Installation of shingles and shakes directly to roof decks covered with a non-permeable underlayment can lead to overheating of the wood and the resulting excessive drying-related defects such as cracking and splitting. Use of a non-permeable membrane can also result in the accumulation of moisture on the underside of the shake or shingle. Over time the resulting moisture buildup can result in fungal degradation of the roof covering. If you find a damaged roof that was constructed using a non-permeable underlayment, a more detailed assessment and analysis of the roof should be conducted to determine the cause of the degradation.

When inspecting a roof, use a worksheet that lists items to be checked and evaluated. The worksheet should include: roof area; age of roof; type and thickness of decking; flashing type and the type of flashing installed in the valleys, roof slope and any slope changes, ridges and intersections with walls; installation and product quality; roof slope; size and type of shakes or shingles; and number and type of damage exhibited by the shakes or shingles. All of these factors are used to make repair versus replace decisions. One should consider replacement of the damaged roof/roof segment when repair cost 80% of the replacement cost. Be sure to factor in relevant replacement product costs associated with hips and ridges, valleys, re-decking, tear-off, and other more complicated area works. Insurance industry claims software or the analysis procedure and Repair Costs Formula (www.cedarbureau.org/cms-assets/documents/24826-485192.cssb-adjusters-guide-to-hail.pdf) can be used to help make this determination.

4.3 Determining Hail Damage

Figure CEDAR-4-1. Hail impact split. Photo courtesy of Haag Engineering.

Figure CEDAR-4-1. Hail impact split. Photo courtesy of Haag Engineering.

Cedar roofs can rebound from minor impacts from hail, leaving virtually no evidence of the storm after normal weathering is allowed to take its course. Furthermore, cedar roofs do not always need to be completely replaced after a hailstorm. Small hail impacts may show up as light-colored spots on the weathered surface of the roof. Larger hail impacts can result in splitting of shakes or shingles, or larger fractures that clearly require replacement. Figure CEDAR-4-1 illustrates a split caused by hail impact. Note the light wood color on the inside of the split.

Figure CEDAR-4-2. Weathering split and small hail impact marks. Photo courtesy of Haag Engineering.

Figure CEDAR-4-2. Weathering split and small hail impact marks. Photo courtesy of Haag Engineering.

Figure CEDAR-4-2 shows a weathering split and impact marks from small hailstones. The gray color along the inside of the split indicates that it is an old split. There is no indication of an impact mark (such as the one shown in Figure CEDAR-4-1) that might have caused the split.

Figure CEDAR-4-3. Many small hail impact marks, but no splits in shingle. Photo courtesy of Haag Engineering.

Figure CEDAR-4-3. Many small hail impact marks, but no splits in shingle. Photo courtesy of Haag Engineering.

Figure CEDAR-4-3 shows many small hail impact marks, but no split. This shingle or shake can be expected to weather to a consistent color within months and does not require replacing.

Figure CEDAR-4-4. Intentional damage from ballpeen hammer (note regular pattern). Photo courtesy of Haag Engineering.

Figure CEDAR-4-4. Intentional damage from ballpeen hammer (note regular pattern). Photo courtesy of Haag Engineering.

Types of damage, including intentional damage, fracture from someone walking on the shingles or shakes, and damage from powerwashing, are shown in Figure CEDAR-4-4, Figure CEDAR-4-5, and Figure CEDAR-4-6 respectively.

Figure CEDAR-4-5. Footfall split damage (note no denting and new cedar color). Photo courtesy of Haag Engineering.

Figure CEDAR-4-5. Footfall split damage (note no denting and new cedar color). Photo courtesy of Haag Engineering.

Figure CEDAR-4-6. Powerwashing damage.

Figure CEDAR-4-6. Powerwashing damage.

4.4 Determining Wind Damage

No specific marks or shape changes can be used to indicate wind damage to a cedar roof. If there is wind damage, it is most likely that fastener pull-through or dislodged fasteners would be visible. These failures likely result from poor quality and/or incorrect fasteners and fastener spacing, or over/under-driven fasteners. These can result in tearing around the fastener head, or roof areas lifting due to lack of fastener holding strength. Loose shakes or shingles, uneven courses where shakes or shingles have slipped out of place, or roofing product that has slid into the gutter or completely fallen off the roof, can be an indication of fastener failure or incorrectly driven or positioned fasteners.

In extreme wind conditions, damage from large windblown debris, such as air conditioning units, is possible. Further investigation will determine if repair or replacement is necessary.

4.5 Determining Fire Damage

Visual clues could be: shakes or shingles charred by fire, damage to sheathing from flame or venting performed by Fire Department when brining the fire under control. The following link will provide additional information: www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_18.pdf.

4.6 Determining Cold Weather Damage

4.6.1 Snow Retention

Determining how much snow is too much can only be determined by the design of the structure, the species of the shake or shingle, grade and dimension of roof rafter lumber. The Canadian Wood Council (www.cwc.ca) and the American Wood Council (www.awc.org) have design/load values on their websites.

Leaving snow on a wood shake or shingle roof for a long period of time will not be detrimental to the shake or shingle. There will be little to no change in the color of the wood shake or shingle.

Dimensional change concerns of radial and tangential grain are addressed in the keyway spacing mandated in the IRC and IBC Codes. With proper keyway spacing, there should be no dimensional change performance issues (i.e., those related to swelling).

Sliding ice and snow are hazards that should be given primary consideration in the total building design. To minimize snow retention, a steeper slope is better. Chimneys should be located at the ridge or gable ends. To minimize corrosion issues, plumbing pipes should be located on inside walls, extending between raters and vented at the ridge. If this is not practical, then plumbing vent pipes should be galvanized iron, well anchored inside the roof. Wide overhangs at the eaves should be avoided as they provide large cold areas for snow and ice buildup. A strip of metal (i.e., drip edge) along the eaves helps shed ice quickly.

More design information for cedar roofs in cold regions is provided here:
www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p17.pdf
www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p18.pdf

4.6.2 Ventilation

Adequate ventilation helps to maintain a cold roof during the winter which will help prevent ice dams and allow improved drying of sheathing if moisture does accumulate. Inadequate ventilation can contribute to mold buildup on roof sheathing inside the attic or biodegradation of the sheathing and roof rafters or trusses.

A cold roof—or vented roof—is recommended. This system allows a constant flow of cold air above the insulation but below the roof covering. The venting space should be sufficient to allow a free flow of air from eave to ridge.

Additional design information can be found here:
www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p17.pdf
www.cedarbureau.org/manuals/imperial/2015/RFI/RoofManual-0407-i-p18.pdf

Ventilation in the attic area allows the bottom of the sheathing to dry in the event the sheathing gets wet due to condensation or a minor leak.

Ventilation also allows the attic area to have lower temperatures during the time of year when ambient outdoor temperatures are high.

4.6.3 Ice Damming

The following documents will provide information on the causes, and “do’s and don’ts” for minimizing ice damming on a roof.

bct.eco.umass.edu/publications/by-title/preventing-ice-dams
www.extension.umn.edu/environment/housing-technology/moisture-management/ice-dams

5. Industry Resources

5.1 Industry Associations

The Cedar Shake & Shingle Bureau is the industry’s trade association. Founded in 1915, it helps a variety of target audiences with technical assistance and product specification. Free educational seminars are available including some approved for AIA credit. Visit www.cedarbureau.org for more information. Knowledgeable District Managers are available to discuss your project.

5.2 Technical Bulletins/Installation Guides

www.cedarbureau.org/cms-assets/documents/26244-377055.difference-between.pdf
www.cedarbureau.org/pdf2013/Specsheet-low-res-03-27-13.pdf
www.cedarbureau.org/installation-and-maintenance/roof-manual
www.cedarbureau.org/cms-assets/documents/24826-485192.cssb-adjusters-guide-to-hail.pdf
www.cedarbureau.org/cms-assets/documents/23180-613565.weather-res-brochure.pdf
www.cedarbureau.org/cms-assets/documents/45094-350971.cmbrochure2011.pdf
www.cedarbureau.org/cms-assets/documents/67060-723658.qcbrochure.pdf
www.cedarbureau.org/purchasing/manufacturers.asp

5.3 Resource Center

The Cedar Shake & Shingle Bureau has resources available on its website to assist with technical issues. District Managers are also available to assist with more advanced questions. Visit www.cedarbureau.org for more information.

5.4 Technical Support Contacts

For support on a project, please contact a District Manager for assistance:
www.cedarbureau.org/about-us/field-staff.asp

5.5 Member Lists

For a list of CSSB members and producers, please refer to this link: www.cedarbureau.org/purchasing

Disclaimer: This manual has been prepared for informational purposes only. RICOWI, IBHS, and the participating roofing industry organizations expressly state that they have no liability, in negligence, tort, or otherwise, with respect to the use of any of the information and/or practices described in this article. The information set forth in this manual is provided in good faith. The user assumes the sole risk of making use of the information provided in this manual.

Users of this manual are strongly urged to follow accepted safety practices, refer to applicable local building codes and standards, and relevant manufacturers’ instructions for appropriate technical requirements, and to work with a qualified professional in order to operationalize the information contained herein. Photographs and examples contained in this manual are provided for illustrative purposes only and do not guarantee the condition of any specific product or the effectiveness of any repair or installation. Nothing contained in this manual is intended or written to be used, nor may it be relied upon or used, by any person and/or business as legal advice.

NOTE: The manual is being completed in sections, and will be released in stages. Check back often to see the most up-to-date edition of the guide.
Please report broken links or other issues to Simon Kellogg (skellogg@ibhs.org).