Key design details & references for wood shingle roofs
Questions & answers about specifications for installation of wood shakes on roofs
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Here we define wood or cedar shake roofing materials & we discuss wood shake roofing installation details and good practices. Sketch at page top is courtesy of Carson Dunlop.
Types of Wood Cedar Shake Roof Application Pattern Details
Unlike their thinner brothers, wood shakes are typically 18"to 24" in length, and up to 14" in width (more than 8" is at extra risk of future splitting).
The roofing shake thickness ranges from 1/2" to 1 1/4" where measured at the shingle butt. The maximum exposure for wood shakes is 7 1/2" (for an 18" long wood shake) or 10" (for a 24" long wood shake), and head lap is 3" or 4" respectively.
A good quality, properly-installed wood shake roof has a life expectancy of 20-40 years. Carson Dunlop's sketch shows the typical cedar shake application pattern and spacing.
Taper-sawn wood shakes are sawn on both sides - like a thick wood shingle
Taper split wood shakes are cut from opposing ends of a wooden block, having a shake butt that is at least 1/2" in thickness and typically are 24" in length. Uncommon, costly.
Hand split, re-sawn wood shakes are similar to straight split shakes (below) but are thicker. A thick split of wood that is rough-split on both sides is re-sawn in half through its thickness to produce two thick shakes, each with a smooth back.
Straight split wood shakes (also called barn shakes ) are split from the same end of a block of cedar (or other wood) and are not tapered. Straight split wood shakes are not usually used on homes.
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.
Wood shake exposures for wood shake 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 wood shake exposure may also vary by the shake grade - something that you might infer by visual inspection of the shakes, matching against wood shake grade definitions, or if a wood hake identification label can be located.
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 shake keyways: 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 shake joints & gap alignment: the gaps or keyways described just above for any pair of abutting wood shakes should have a side-lap offset of no less than 1 1/2" from the joints or keyways in adjacent shake courses (horizontal rows of wood shakes across the roof), and in any three wood shake courses no two joints should be in direct alignment (gaps should not be over gaps in any three shake courses).
For added details about proper wood shake roof installation, 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).
Wood Shake Roof Installation Specifications - Best Practices
Whether installed over spaced or solid sheathing, shakes
should always be interlaid with 18-inch-wide strips of
No. 30 roofing felt. The felt strips acts as baffles to keep
windblown snow and other debris from penetrating the
roof system during extreme weather. The felt “interlayment”
also helps shed water to the surface of the roof.
It is
important to locate each felt strip above the butt of the
shake it is placed on by a distance equal to twice the
weather exposure (Figure 2-51 shown below).
[Click any image or table for an enlarged, detailed view.]
Placed higher, the felt strips will be ineffective. Placed
too low, they will be visible in the keyways and will wick
up water, leading to premature failure of the shakes. In
addition, follow these guidelines:
For the starter course, use either a single layer of shakes
or two layers separated by a strip of felt interlayment
(installed up from the eaves by a distance equal to the
weather exposure). Fifteen-inch shakes are available
for the bottom layer of a double starter course
Each shake gets two nails about
3/4
inch in from each end
and 1
1/2
inches above the butt line of the overlaying shake.
The first course should overhang the fascia by
1
1/2
inches.
All courses should overhang the rake trim by about
1 inch.
Leave a gap between adjacent shakes of
3/8
to
5/8
inch for
expansion when wet.
Offset joints in successive courses by at least 1
1/2
inches
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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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