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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.
ASHI home inspection education class notes on how to inspect slate roofs
by 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 inspected?
much life remains? Stratford-on Avon Saxon
chapel, 1100 years +!
repairs are needed?
will it cost to repair or maintain?
Identifying Slate Roofs
style, one or many colors
style, varying thickness & texture
Graduated Slate, varying
size, smaller, thinner at ridge
look-alikes and replacement materials
Safety of the inspector comes first - Do not walk-on it
ground - unreliable
at edge - reliable
nearby windows/surfaces - good
- 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)
of maintenance (repair history, competence)
failures (quality, age, condition, leaks)
& fastener failures (common)
failures (most common)
Installation patterns (uncommon)
Quality of Slate
is stone, unique to quarry where mined
and appearance are clues but not sure
"weathering" for each of above, not a durability factor
Slate Colors (continued)
purple, black, red also avail - Vermont, most
common, lower in lime than PA = 100-200 yrs.
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.
un-fading - Washington County NY
Quality of Slate
in thickness - more is better
in stone chemistry - quarry-unique
and inclusions - iron & calcite
Ribbon slate - impurities
in bands, shorter life, may vary depending on what minerals make up the color
replacement slates - how
fastening methods -hooks, tabs
patches - with metal or other
or roof mastic - "the bigger the blob the better
or missing slates - how many?
or ridge caps worn, rusted, leaky
along cleavage planes
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
missing slates, many patches
pops - vibration, high nails -> holes
Over-nailing - too tight -> cracks
Iron vs. copper/stainless nails - fastener failures - many slates may be about to fall
roll roofing valley liners
or steel valley liners
flashings - usually tarred
Inspect leak history in attic - flashings & ice dams
patterns more likely to leak
Dutch Lap (smaller slates 10x6"?)
Open Lap - good for barns
lap patterns, solid or mixed
sizes up to
24x14", square ends, uniform color & exposure
Slate - look
for on Tudor's, rough surface, varied thickness
Graduated Slate - graduated
size & exposure
Sketches of Slate Patterns
Slate Inspection Mistakes
"Pass" a Worn Out Slate Roof: Criteria
than 25% of slates are sliding down - fastener failure
than 25% of slates are worn out - big replacement cost
"Fail" or Replace a Good Slate Roof
repairs, few current loose/bad slates
flashings, good slates
roofer sells owner on avoiding maintenance cost, removes 300-year material,
installs 30-year material
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FAQs below discusses field reports of problems & solutions for this topic
Frequently Asked Questions (FAQs) about how to inspect the condition of slate roofs for age, remaining life, wear, damage, leaks
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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).
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.