Slate Roof Leaks, how to find and diagnose leaky slate roofs
How to inspect, evaluate & repair slate roofs - the basics
Source list for replacement roofing slate & slate alternatives
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This series of detailed slate roof inspection and repair articles describes procedures for evaluating the condition of slate roofing. How to inspect, identify defects, and estimate remaining life of slate roofs are addressed. The article series also references slate repair procedures, repair slate sources, and slate quarries.
All slate roofs probably have at least some flashing, slate, or other
damage or mechanical installation errors. Some conditions such as
a side lap error, damaged slate, or even flashing error may leak only
in certain weather conditions such as windy rain storms from a particular
direction, water backup behind ice dams, or prolonged rains.
Where
slates are missing near valleys the adjoining slates may be damaged
as well. Openings may cause leaks or water to pass below the valley
flashing even if the flashing looks intact. Where there were previous
repairs it's common for the felt underlayment to be torn as well.
If there are porous slates or openings above the tears in the felt,
water may leak through.
Ice dams at roof eaves can be a serious leak source on slate as most
other roof systems. Traditionally 30# felt was used at eaves as "insurance"
against this problem. Some slate suppliers recommend this heavier
felt for all underlayment, not just at the eaves. However two components
conspire to reduce the effectiveness of felt as ice-dam protection:
every nail at the eaves punctures the felt, and with age felts often
dry and disintegrate before the slates have worn out.
Ice
dam protection is improved in new or re-roof applications using the
newer sticky membranes such as WR Grace's Ice and Water ShieldTM.
However the preferred solution to this problem is proper attic ventilation.
Good venting avoids the ice-dam problem and adds reductions in winter
moisture and summer heat problems. Old houses whose attics have been
converted to living space, particularly with un-vented ceilings following
the underside of fully-insulated roofs are likely to be serious moisture
and heat traps.
Slope requirements for slate roofs
In conventional roofing design slates are used on roofs with a slope
of at least 4" of rise in 12" of run, that is, on 4 in 12 roofs. A
3" head lap is used, often 4" when the slope is less than 8 in 12.
So a 20" long slate, with a 3" head lap, would have an exposure of
8.5". For 18" slates the exposure is 7.5", and for 16" slates, 6.5".
Roofs with less head lap or more exposure may be more leak-prone.
Some slate companies advertised A slate roof that cannot leak,
yet [was] inexpensive, easy to apply, beautiful..., durable as time,"
using a design which was soon found to be a disaster: 12" slates
were placed with 9" exposure, leaving 3" for headlap and 6" which
was backed only by a cap sheet of 32# felt interlaced with the slates.
Roofs were also installed following this poor design, using 14" slates
with 10"-11" exposure.
Felt is not functional as a permanent roofing
material: even where it is not exposed directly to sunlight, as the
organics dry out the felt cracks, disintegrates, and leaks. We have
reports that inspectors have been the subject of legal
actions following their failure to identify this defect in slate roofs.
See the illustrations above.
Personal communication, Doug Sheldon, Vermont Structural
Slate, December 1990.
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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.)
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).
Slate Roofs , Steven Trapasso, presentation to NY Metro
ASHI, Inc. chapter seminar, November 1990.
The Old-House Journal , Special Roof Issue , April
1983, The Old-House Journal, PO Box 50214, Boulder, CO 80321-0214
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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