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 Inspecting Slate Roofs - Class on how to inspect slate roofing for condition, damage, leaks
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Slate roof inspection class, free, online: this is a classroom presentation on the inspection, diagnosis, and estimate of remaining life of slate roofs. It was made to home inspectors in New York and has been used in other states in the U.S.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
ASHI home inspection education class notes on how to inspect slate roofs
Daniel Friedman
Hudson Valley ASHI - HVASHI Seminar - Kingston, New York
9 September 2003 class for home inspectors
This course outline reviews key considerations in evaluating slate roofing on historic or other buildings. Its presentation is intended to
be accompanied by a collection of photographs and drawings. As time permits the author will place in this document links to representative samples of those illustrations.
Readers of this page should see Slate Roofs by Alan Carson and Daniel Friedman, for
a detailed description of slate roof inspection procedures, slate roof materials, slate roof defects, slate and slate replacement sources.
Key Questions to ask about slate roofs
- Is
it slate?
- How
is it inspected?
- How
much life remains? Stratford-on Avon Saxon
chapel, 1100 years +!
- What
repairs are needed?
- What
will it cost to repair or maintain?
Identifying Slate Roofs
- Standard
style, one or many colors
- Textured
style, varying thickness & texture
- Graduated Slate, varying
size, smaller, thinner at ridge
- Not-Slate
- asbestos-cement
shingles
- slate
look-alikes and replacement materials
Inspecting Slate
- Safety of the inspector comes first - Do not walk-on it
- From
ground - unreliable
- Ladder
at edge - reliable
- From
nearby windows/surfaces - good
- Binoculars
- useful, incomplete
- Document inspection limitations & implications (hidden slopes often differ in materials, condition,
and may not even be slate!)
Slate Roof Life
- Quality of Slate (Vermont-NY,
Pennsylvania, Virginia Buckingham)
- Level
of maintenance (repair history, competence)
- Material
failures (quality, age, condition, leaks)
- Fasteners
& fastener failures (common)
- Flashing
failures (most common)
- Installation patterns (uncommon)
Quality of Slate
Slate
is stone, unique to quarry where mined
Color
and appearance are clues but not sure
- Black
- Blue-black
- Purple
- Mottled-purple
& green
- Red
- "unfading" vs.
"weathering" for each of above, not a durability factor
Slate Colors (continued)
- Green,
purple, black, red also avail - Vermont, most
common, lower in lime than PA = 100-200 yrs.
- Gray,
gray-black - Vermont & New York lighter than
PA slate, may include purple, green.
- Blue-gray - Pennsylvania -
best known, "Pennsylvania black" - less
durable - 40-50 yrs. White efflorescence forms rings on 3 exposed sides.
Unfading PA gray is soft-gray, longer-lived; Unfading PA black is rougher,
longer-lived; Blue-black "hard-vein" PA slates darken with age.
- Blue-gray - Virginia - tough, >100-200 yrs.
- Red
un-fading - Washington County NY
Quality of Slate
-
Variations
in thickness - more is better
-
Variations
in stone chemistry - quarry-unique
-
Imperfections
and inclusions - iron & calcite
-
Ribbon slate - impurities
in bands, shorter life, may vary depending on what minerals make up the color
bands
Slate Maintenance
- replacement slates - how
many?
- replacement
fastening methods -hooks, tabs
- temporary
patches - with metal or other
- tar
or roof mastic - "the bigger the blob the better
the job?"
- loose
or missing slates - how many?
- valleys
or ridge caps worn, rusted, leaky
Material Failures
Weathering:
- delaminating
- scaling
along cleavage planes
- science: slate
becomes thin or soft and spongy: mineral impurities (calcite, iron sulfides) +
alternating wet/dry cold/hot form gypsum which expands and delaminates the
slate. Slate is stone, it does not "rot" but it does get soft.
- white mineral salt rings may
telltale degree of aging, some slaters opine that the area of the un-stained
center defines the % remaining life - no science given
Fastener Failures
- Many
missing slates, many patches
- Nail
pops - vibration, high nails -> holes
- Over-nailing - too tight -> cracks
- Iron vs. copper/stainless nails - fastener failures - many slates may be about to fall
Flashing Failures
- Mineral
roll roofing valley liners
- Copper
or steel valley liners
- Chimney
flashings - usually tarred
- Inspect leak history in attic - flashings & ice dams
Installation Patterns
- "Cheap"
patterns more likely to leak
- Dutch Lap (smaller slates 10x6"?)
- French Method
- Open Lap - good for barns
- Standard
lap patterns, solid or mixed
- sizes up to
24x14", square ends, uniform color & exposure
- Textured
Slate - look
for on Tudor's, rough surface, varied thickness
- Graduated Slate - graduated
size & exposure
Sketches of Slate Patterns
- Dutch Lap
- French method
- Open Lap
- Standard Pattern
Slate Inspection Mistakes
Don't
"Pass" a Worn Out Slate Roof: Criteria
- more
than 25% of slates are sliding down - fastener failure
- more
than 25% of slates are worn out - big replacement cost
Don't
"Fail" or Replace a Good Slate Roof
- many
repairs, few current loose/bad slates
- bad
flashings, good slates
- asphalt-shingle
roofer sells owner on avoiding maintenance cost, removes 300-year material,
installs 30-year material
Frequently Asked Questions (FAQs) about how to inspect the condition of slate roofs for age, remaining life, wear, damage, leaks
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- "Slate
Roofs," Alan Carson, Dan Friedman, ASHI Tech Journal Vol1 No1 - from ASHI,
www.ashi.com
- The Slate Roof Bible, Joseph Jenkins, www.jenkinspublishing.com
- "Slate
roofing: an old-world tradition," Professional Roofing, February 1993
- "Special
Roof Issue", Old House Journal, April 1983
- Handbook of Building Crafts in Conservation, Jack Bower, 1981
- Vermont
Structural Slate Co., Fair Haven VT, 802-265-4933
- Evergreen
Slate Co., & Hilltop Slate Co., both in Granville, NY
- Buckingham
Slate Co., Richmond, VA.
- How to Inspect and Repair Slate Roofs - Detailed Procedures for Inspection and Repair of Slate Roofs - ASHI Technical Journal, 1991, Updated 2006
- Slate Roofs: a photographic library of slates, slate roofs, roofing styles
- 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
- Handbook of Building Crafts in Conservation, Jack Bower, Ed.,
Van Nostrand Reinhold Company, NY 1981 ISBN 0-442-2135-3 Library of
Congress Catalog Card Nr. 81-50643.
- Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008)
ISBN-10: 0471788368
ISBN-13: 978-0471788362
- 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
- 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
- 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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