Slate Roofing: how to evaluate ribbon slates on a roof
How to inspect, evaluate & repair slate roofs - the basics
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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.
The ribbon slate on this
mansard roof slope may have been chosen for appearance, though it was not installed so as to use the ribbon diagonals to form any particular pattern.
In the first two photos at left the slates have diagonal
colored stripes of mineral inclusion, but they do not show the characteristic delamination and wear we see
on classic ribbon slates.
Some ribbon slates were a cheaper and shorter-lived product because the mineral inclusions that formed the "ribbons" of color in the roofing slates were a softer material that weathered out of the slate rapidly. However as numerous slate roofers and other readers have pointed out, ribbon slates were also selected and installed on some buildings for their aesthetic appeal and included ribbon slates from other quarries whose mineral inclusions were quite durable. So the answer to the question of "are ribbon slates more or less durable than other roofing slates?" is "it depends" on which quarry was the source of the slate.
More slate with diagonal mineral inclusions is shown mixed with solid reds on other slopes of the same home.
More rather worn ribbon slates on a New York home.
We'll post other(sharper focused and close-up) examples of ribbon slate in this article.
"Slate is of medium hardness, very fine grained of low porosity, great
strength and consists essentially of insoluble and stable minerals
that will withstand weathering for hundreds of years. Some slate in
Pennsylvania contains ribbons which consist of narrow original beds
usually containing carbon, and darker in color than in the body.
There
is tendency for some ribbons to contain an excessive amount of the
less resistant minerals, and they should not appear on exposed surfaces." -- Dr. Oliver Bowles, Mineral Technologist of the US Bureau of Mines,
in "The Characteristics of Slate" , June 1923 paper delivered
to the American Society for Testing Materials. ASTM.
By "appear," Bowles meant that inferior ribbon slates which contain
fast-weathering mineral inclusions should not be used where exposed to the weather.
Ribbon slates are easily identified from the ground. The stripes are
accentuated because the ribbon portion absorbs more water than the
rest of the slate. Usually the ribbons are darker, often multi-colored
browns and reds. An Albany NY slate roofer
suggests that ribbons were desirable
for a pattern effect, and that they were equally durable with other
slates from Pennsylvania. -- Capital Region ASHI
chapter education seminar, fall 1990
Some roofers consider ribbon slates as less durable material.
we suspect that the durability of
ribbon slates depends on the particular minerals which make up the
visual diagonals. If the diagonals are comprised of minerals softer
than the surrounding slate, early wear is likely. In at least some
cases, ribbon slates are less durable than other Pennsylvania slates. -- Trapasso,
personal communication.
If these slates were actually shorter-lived than clear cut materials,
why were they used? In the 1940's one square (100 sq. ft.) of Pennsylvania
slate cost about $6.00, or about $15.00 installed. Because of these
attractively low prices and low anticipated replacement cost [boy
were they wrong!] ribbon slates were very popular and were
used extensively.
As slate and roofing costs rose and as ribbon slates
were less expensive than clear slates, some clever roofers used slates
which were cut so that the ribbons were only in the upper half of
the slate. As the ribbons were covered by the next course, these roofs
were more durable.
An inspector may spot this interesting material from attic view
or from outside if a slate has fallen
out of position, exposing the upper half of its predecessor course.
The cost of installing a modern slate roof makes the choice of poor
materials illogical.
Attic view means inspecting the underside of the roof surface from
inside the building. If open or spaced sheathing was used as nailing
base for the slates you'll be able to see the backs of the slate material,
or in some cases, you'll see roofing felt, usually damaged or soft,
which may provide openings to see the slates. Where closely-spaced
board sheathing was used you'll not see slates except perhaps through
a knot hole or damaged board.
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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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