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Types of Roofing Slates & Types of Slate Roofing
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Types of slates used on building roofs. 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.
Types of Slate used in Roofing
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 An earlier version of this article appeared in the winter 1991 issue of the ASHI Technical Journal - the content has been edited and extensively updated for this online version: we've corrected the original text, added extensive explanatory text, and added numerous photographs of the conditions we discuss. Copies of the ASHI Technical
Journal are available from the American Society of Home Inspectors - ASHI at ashi.com.
The abandonment of perfectly good slate roofs which should have been repaired
is a financial shame and the destruction of a valued asset.
At the
same time, careless optimism about a bad slate roof which is at the
end of its life risks an angry inspection client. This article reviews
types of slate, common defects, inspection topics, and some repair
tips. We also provide slate sources and where to buy slate roofing materials and slate roofing tools and products.
Variations occur in color, thickness, surface texture, graduated sizes
and varying widths. Standard slate roofs use slates 3/16" to 1/4"
thick of one uniform length and width with square tails laid to a
line in a conventional shingling pattern.
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Textural style roofs use rough-textured slates with uneven butts and
varied thickness. Different colors and varying sizes are often used.
The resulting roof has a very rustic look.
Graduated slate roofs use slates which vary in size and often in thickness,
with larger slates at the eaves, smaller and with less shingle exposure
at the ridge. Original work graduated
roofs show smooth transition among the sizes from larger to smaller
as each course of slates approaches the ridge line. Where lots of
repair work was done this effect may have been lost. This roof style
makes the roof and building look larger and taller than it actually
is.
Shingle exposure is the portion of the shingle which you can see from
outside, or the portion left exposed to the weather. In most shingle
roofing systems the exposed portion of the shingle is considerably
less than the total shingle length.
In addition to color, graduated and textural patterns, slates are
placed in a variety of shingling patterns, of which several are illustrated
in sketches throughout this paper and in the Slate Roof Photo Library, such as French, Dutch-lap, and
open-lap patterns.
The Dutch lap uses a 3" side overlap
and a vertical exposure of all but 3" of the slate. The result is
essentially a single layer of roofing with only 3" of overlap at the
top and side. The open joints are all on one side or the other along
any given row or course of slates. This system is extra vulnerable
to wind-driven rain.
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 The
French method slate pattern also offers essentially
a single layer of roofing with three inches around the perimeter of
each shingle.
Finally, slates have a natural "grain" in the material. Normally the
slates are cut so that the grain runs the length of the slates.
If
the slate is quarried improperly, the nail holes create a perforated
effect on the slate and it will break in half at the nail holes after the installation. Watch for this interesting defect.
See this slate edge close up, showing the natural layering of mineral deposits in the original stone.
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Frequently Asked Questions (FAQs) the different types of roofing slate
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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Alan Carson and Dan Friedman are ASHI Members, home inspectors,
educators and writers in Toronto and Poughkeepsie respectively. Information
in this article is taken from the references shown below, from inspection
experience, from opinions shared at ASHI and other education seminars,
from the authors' personal, limited experience repairing and rebuilding
of slate roofs, and from very helpful Bill Markcrow and Doug Sheldon
at Vermont Structural Slate Co. we also paraphrased from a presentation
to NY Metro ASHI Members by Mr. Steven Trapasso in October, 1990.
Mr. Trapasso has 40 years experience in working with slate, and has
a clear love affair with the material, particularly when it comes
from Vermont.
- 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.
- 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.
- Slate Roofing Contractors Association of North America
- National Slate Association includes list of slate testing laboratories
- Vermont Structural Slate Co., PO Box 98 Fair Haven, VT
05743 802/265-4933 802/265-3865 FAX (Green, purple, unfading red,
and Spanish imported black.)
- Rising & Nelson Slate Co., West Pawlet, VT 05775; 802/645-0150
(all VT colors plus Buckingham Gray from VA and blacks from PA.)
- Evergreen Slate Co., 68 Potter Ave., Granville, NY 12832;
518/642-2530. Vermont slates in 10 colors.
- Hilltop Slate Co., Middle Granville, NY 12849; 518/642-2270
(all VT colors plus imported Spanish Black)
- Structural Slate Co., Pen Argyl, PA 18072; 215/863-4145
(PA black)
- Buckingham Slate Co., 4110 Fitzhugh Ave., Richmond, VA
23230; 805/355-4351 (VA Buckingham Grey)
- Eternit, Inc., rigid fiber reinforced cement roofing slates
(and board products. Village Center Drive, Reading, PA 19607 800/233-3155
- BritSlateTM are made from 100% quarried slate particles
combined with an adhesive (epoxy?) and no fillers with no questionable
side effects according to the manufacturer. According to the manufacturer,
they can be cut, drilled, etc. and come with a 50-year guarantee.
They're less prone to breakage than slate, fireproof, and do not absorb
water (like natural slate), and do not encourage organic growth (moss
and lichens) because they are not porous. BritSlate North America,
Inc., 647 West Boylston St., Worcester, MA 01606 508/852-4888 508/852-7224
FAX 2/90.
- Reinforced-cement shingles which "look like slate but are
lighter and one-third the cost" are available from Atlas International
Building Products, 5600 Hochelaga St., Montreal, Quebec, Canada H1N
1W1. [$180/square loose or $400./sq. installed, 30-year guarantee.]
- Supra-Slate "looks like slate and is manufactured in colors
of real quarry slate." Tegusol is a double interlocking clay roof
tile. Available from: Supradur Manufacturing Corporation, PO Box 908,
Rye, NY 10580 800/223-1948 or 914/967-8230. or 122 East 42nd St.,
NY, NY 10168 212/697-1160
- Lifetile(R) Boral Concrete Products, Inc., produces high
density extruded concrete roofing tiles meeting Class "A" requirements.
Dallas, TX 214/544-2227
- 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
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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