Key design details & references for wood shingle roofs
Questions & answers about how to inspect wood roofs: wood shingles or wood shakes
Here we outline key inspection points for wood or cedar shake roofs, addressing shingle type, felt underlayment, shingle exposures, wood shingle keyways or gaps, wood shingle joints, and proper wood roofing shingle fasteners, installation details and good practices.
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The wood shingle roof inspection details outlined below are paraphrased from information provided by the Cedar Shake & Shingle Bureau, the recognized wood roofing authority since 1915 and from information provided by Carson Dunlop a Toronto company offering home inspections, home inspection publications, and home inspection education.
Wood Roof Leaks: Inspect inside the building for evidence of roof leaks, accessing the attic or under-roof space if it is readily accessible, and if not, inspect for indirect evidence of roof leaks such as leak stains on ceilings or at the ceiling/wall juncture of the building's highest floors.
Common leak points on most roofs include at roof penetrations such as chimneys and plumbing vents and in northern climates, at the roof eaves where ice dam build-up may be a leak source.
Remember to look closely for leaks below roof valleys and at roof-wall abutments where a lower roof slope abuts a higher building section sidewall.
Visible damage to roof shingles, flashing, or other on roof components: inspect from outside for these conditions.
Also include noting the presence of encumbrances such as moss on a wood roof [photo] because that material holds moisture and thus can accelerate wood roof wear
Shingle exposures for wood roofs: the maximum weather exposure for wood shakes or wood shingles depends on the shingle size and the slope or pitch of the roof.
Allowable shingle exposure may also vary by the shingle grade - something that you might infer by visual inspection of the shingles, matching against wood shingle grade definitions, or if a shingle identification label can be located.
Roof Slope or Pitch
Maximum Wood Shingle Exposure on Roofs
Grade No. 1 Blue Label Shingles
Grade No. 2 Red Label Shingles
Grade No. 3 Black Label Shingles
Shingle Length
Shingle Length
Shingle Length
16"
18"
24"
16"
18"
24"
16"
18"
24"
3/12 - 4/12
3 3/4"
4 1/4"
5 3/4"
3 1/2"
4"
5 1/2"
3"
3 1/2"
5"
4/12 & steeper
5"
5 1/2"
7 1/2"
4"
4 1/2"
6 1/2"
3 1/2"
4"
5 1/2"
Roof Slope or Pitch
Maximum Wood Shake Exposure on Roofs
Wood Shake Length
18"
24"
4/12 & steeper roofs
7 1/2"
10" (Note)
Note: 24" x 3/8" handsplit wood shakes are limited to 7 1/2" weather exposure, or 5" exposure where the Uniform Building Code is in application.
Wood shingle or shake keyways or gaps: the gap or space between adjacent wood shingles should be between 1/4" and 3/8" in width.
For wood shakes the keyway should be 3/8" to 5/8" in width.
The Shingle Bureau points out that the gap observed between shingles or shakes on a wood roof will vary depending on ambient moisture conditions as moist wood shingles or shakes swell (which is why we need a gap, to avoid buckling and splitting).
Wood shingle keyways or gaps are illustrated at the top of this page.
Wood shingle/shake joints & gap alignment: the gaps or keyways described just above for any pair of abutting wood shingles or shakes should have a side-lap offset of no less than 1 1/2" from the joints or keyways in adjacent shingle courses (horizontal rows of shingles across the roof), and in any three shingle courses no two joints should be in direct alignment (gaps should not be over gaps in any three shingle courses).
Shingle type and grade identification: every bundle of wood shingles or wood shakes sold and delivered is required to include an identifying label, secured under the band that holds the bundle of shingles together. The label identifies the shingle manufacturer, a reference to model building code approval, the type of wood shingle product, and the grade of the shingle, the approving wood shingle grading agency, and the wood shingle (or shake) product's dimensions.
At an older wood-roofed structure these labels may have long been thrown away, but if you are inspecting a new wood roof installation the labels should be available either on un-used shingle bundles or on occasion we've found the identifying label in piles of roof installation debris.
Wood shingle fasteners: should be corrosion-resistant, hot-dipped zinc-coated ("galvanized") or aluminum or stainless steel nails (or staples as allowed in some jurisdictions) and should conform to ASTM A641. Do not use blued steel or copper nails on wood roofs. Nails should be driven flush with the shingle or shake top, but not driven into (and crushing) the shingle or shake.
Wood roof nails should be 3/4" (or 1" per UBC) from the shingle side edge and 1 1/2" (or 2" per UBC) above the butt line of the following shingle course (row). When inspecting an existing wood roof completely installed, do not pry up shingles to inspect the nails as you are likely to cause damage.
But the nailing pattern may be visible from inside of an un-finished attic, depending on the thickness and type of roof decking. More details about wood roof nails and nailing patterns are provided at WOOD ROOF INSTALLATION SPECS.
Wood Shake Roof Felt Underlayment: on wood shake roofs, a 15# felt underlayment is recommended, using an 18" wide strip of roofing felt. (The Uniform Building Code specifies use of 30# felt.) The felt is placed over the top portion of the shake course at a distance above the butt equal to twice the weather exposed amount of the shake.
Carson Dunlop's sketch shows the typical cedar shake application pattern and spacing.
Here Carson Dunlop's sketch shows typical cedar shake nailing details & pattern and exposures.
Notice that for this example cedar shake roof a felt interlay is installed between every course of shakes.
Questions & Answers regarding this article
Questions & answers about how to inspect wood roofs: wood shingles or wood shakes.
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Additional technical contributors & reference sources for this article are listed below.
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"Choosing Roofing," Jefferson Kolle, January 1995, No. 92, Fine Homebuilding, Taunton Press, 63 S. Main St., PO Box 5506, Newton CT 06470 - 800-888-8286 - see http://www.taunton.com/FineHomebuilding/ for the magazine's website and for subscription information.
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
Cedar Shake & Shingle Bureau, CSSB, U.S.: Sumas, WA 98295-1178, Tel: 604-820-7700, In Canada:
Cedar Shake and Shingle Bureau #2 - 7101 Horne Street, Mission, BC V2V 7A2 Tel: (604) 820-7700, E-mail: info@cedarbureau.com , website: http://www.cedarbureau.org/
CCSB offers wood shingle installation instructions in the form of a manual - cedarbureau.org/installation/wall_manual/introduction.htm
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
Architectural elements: the technological revolution: Galvanized iron roof plates and corrugated sheets; cast iron facades, columns, door and window caps, ... (American historical catalog collection), Diana S Waite, available used out of Amazon.
Green Roof Plants: A Resource and Planting Guide, Edmund C. Snodgrass, Lucie L. Snodgrass, Timber Press, Incorporated, 2006, ISBN-10: 0881927872, ISBN-13: 978-0881927870. The text covers moisture needs, heat tolerance, hardiness, bloom color, foliage characteristics, and height of 350 species and cultivars.
Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Key questions to ask at each stage of the green building process Tested tips and techniques for successful structural design
Construction methods for new and existing buildings
Information on insulation, drainage, detailing, irrigation, and plant selection
Details on optimal soil formulation
Illustrations featuring various stages of construction
Best practices for green roof maintenance
A survey of environmental benefits, including evapo-transpiration, storm-water management, habitat restoration, and improvement of air quality
Tips on the LEED design and certification process
Considerations for assessing return on investment
Color photographs of successfully installed green roofs
Useful checklists, tables, and charts
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
Roofing The Right Way, Steven Bolt, McGraw-Hill Professional; 3rd Ed (1996), ISBN-10: 0070066507, ISBN-13: 978-0070066502
Slate Roofs, National Slate Association, 1926, reprinted 1977
by Vermont Structural Slate Co., Inc., Fair Haven, VT 05743, 802-265-4933/34. (We recommend this book if you can find it. It
has gone in and out of print on occasion.)
Roof Tiling & Slating, a Practical Guide, Kevin Taylor, Crowood Press (2008), ISBN 978-1847970237, If you have never fixed a roof tile or slate before but have wondered how to go about repairing or replacing them, then this is the book for you. Many of the technical books about roof tiling and slating are rather vague and conveniently ignore some of the trickier problems and how they can be resolved. In Roof Tiling and Slating, the author rejects this cautious approach. Kevin Taylor uses both his extensive knowledge of the trade and his ability to explain the subject in easily understandable terms, to demonstrate how to carry out the work safely to a high standard, using tried and tested methods.
This clay roof tile guide considers the various types of tiles, slates, and roofing materials on the market as well as their uses, how to estimate the required quantities, and where to buy them. It also discusses how to check and assess a roof and how to identify and rectify problems; describes how to efficiently "set out" roofs from small, simple jobs to larger and more complicated projects, thus making the work quicker, simpler, and neater; examines the correct and the incorrect ways of installing background materials such as underlay, battens, and valley liners; explains how to install interlocking tiles, plain tiles, and artificial and natural slates; covers both modern and traditional methods and skills, including cutting materials by hand without the assistance of power tools; and provides invaluable guidance on repairs and maintenance issues, and highlights common mistakes and how they can be avoided.
The author, Kevin Taylor, works for the National Federation of Roofing Contractors as a technical manager presenting technical advice and providing education and training for young roofers.
The Slate Roof Bible, Joseph Jenkins, www.jenkinsslate.com,
143 Forest Lane, PO Box 607, Grove City, PA 16127 - 866-641-7141 (We recommend this book).
Solar heating, radiative cooling and thermal movement: Their effects on built-up roofing (United States. National Bureau of Standards. Technical note), William C Cullen, Superintendent of Documents, U.S. Govt. Print. Off (1963), ASIN: B0007FTV2Q
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
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