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Slate Roof Leak Diagnosis & Repair
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
How to find the source of leaks in a slate roof: 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. 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.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
How to Track Down the Source or Point of Leaks in Slate Roofs
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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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- How to Inspect & Repair Slate Roofs a detailed article about evaluating the condition of slate roofing and repairing worn or damaged slate roofs.
- Slate Roof Photo Library photographs of colors, types, patterns of slate roofs, slate roof wear, slate roof conditions.
- Slate References page from the ASHI Technical Journal
- Slate Sources, Repairs page from the ASHI Technical Journal
- Roofing: Defect Recognition, Repair, Prevention for Roofing & Flashing main web page
- Inspecting and Evaluating Slate Roofs Hudson Valley ASHI seminar content
- Choosing a Roofing Contractor How to find and select a roofing contractor - (thanks to Jessie Schrader)
- 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
- National Slate Technology Center courses for architects, builders, etc.
- Slate Roofing Contractors Association of North America
- National Slate Association includes list of slate testing laboratories
- Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724
ISBN-13: 978-0471331728
- Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008)
ISBN-10: 1405161035
ISBN-13: 978-1405161039
- Historic Slate Roofs : With How-to Info and Specifications, Tina Skinner (Ed), Schiffer Publishing, 2008, ISBN-10: 0764330012
, ISBN-13: 978-0764330018
- 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).
- Slate Roofing in Canada (Studi4es in archaeology, architecture, and history),
- Smart Guide: Roofing: Step-by-Step Projects, Creative Homeowner (Ed), 2004, ISBN-10: 1580111491, ISBN-13: 978-1580111492
- Tile Roofs of Alfred: A Clay Tradition in Alfred NY
- "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
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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