Inspecting Slate Roofs - how to inspect slate roofing for condition, damage, leaks InspectAPedia® -
Course notes on slate roofing inspection, diagnosis, repair
Roofing inspection course
Home inspection classes
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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
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
corroded
tarred
leaky
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
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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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