Slate Roof Repair History

How to spot previous repairs to a slate roof
Types of repairs to slate roofs that can be seen from the ground, from roof edge, or from closer inspection points
How do previous roof repairs help track down current roof leaks or troubles in a slate roof?
How does the roof repair history help decide on the remaining life of a slate roof or the cost to maintain a slate roof
Questions & Answers about assessing a slate roof condition by observing its repair history
References

Click to Show or Hide Related Topics

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Slate roof repair history: the repair history of a slate roof can help you assess the remaining roof life, roof condition, probable roof leak points, and the expected cost of maintaining a slate roof. Here we include photos and text that help a roof inspector or building owner spot where repairs have been made to a slate roof, why the repairs were made, what was probably wrong, and what, thus, is the overall condition of the roof.

Slate Roof Repair history helps diagnose the condition of a slate roof

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. An earlier version of this article appeared in the winter 1991 issue of the ASHI Technical Journal - the content has been edited and updated for this online version - March 2010. Copies of the ASHI Technical Journal are available from the American Society of Home Inspectors - ASHI at ashi.com.

Tar or roofing mastic is normally an indication of improper maintenance. It should be considered a temporary, unreliable repair. Tar or roofing cement should not be found at chimneys, sidewall flashings, plumbing vents, or elsewhere.

Our photo at left shows tar patching in the dormer valley and below the dormer. But further loose slates are falling off of this roof, possibly damaged during application of the valley tar.

The tar itself usually remains effective as a sealant only for a year or so. While in place, tar traps moisture within the slates, causing the slate itself to deteriorate. When flashings leak on a roof they should be repaired or replaced as necessary, without using roof cement.

Copper tabs and fastener failures on slate roofs: Watch for numerous copper tabs at the center of replacement shingles. These indicate that repairs have been made and they may be a clue about the overall condition of the fasteners. In a first-class slate repair you should not be able to see the copper tabs. The Old-House Journal April 1984 roofing issue describes an alternative method for securing slates which will leave a copper tab exposed. Expert roofers have a less visible method of fastening the replacement slate. [See "Repairing Slates" sidebar article.]

Our page top photo shows a perfectly good repair made by sliding a piece of copper flashing up under slates to cover a hole that may have been made by a nail pop from below.

Asphalt shingles applied over slate roofs: Using asphalt over slates is surprisingly common "re-roof" procedure as it avoids labor and disposal costs for the slate material. [In some areas of the Northeast it also represents the popularity of lower-cost asphalt and the dearth of experienced slaters who might have repaired the slate roof.]

When nailing the asphalt shingles it is common to find only a poor bond of new nails to original roof decking. The slates below tend to chip and bulge the new material resulting in a "peanut brittle" or "popcorn" effect. Since the comparatively large thermal mass of the slates retains heat, the asphalt shingles are "cooked" from their backside as well as from their front when exposed to sunlight. The life of such shingles is estimated by some to be half the normal span.

Leaks in Slate Roofs

All slate roofs probably have at least some flashing, slate, or other damage or mechanical installation errors. Some conditions such as a side lap error, damaged slate, or even flashing error may leak only in certain weather conditions such as windy rain storms from a particular direction, water backup behind ice dams, or prolonged rains.

Where slates are missing near valleys the adjoining slates may be damaged as well.

Openings may cause leaks or water to pass below the valley flashing even if the flashing looks intact. Where there were previous repairs it's common for the felt underlayment to be torn as well. If there are porous slates or openings above the tears in the felt, water may leak through.

Ice dams at roof eaves can be a serious leak source on slate as most other roof systems. Traditionally 30# felt was used at eaves as "insurance" against this problem. Some slate suppliers recommend this heavier felt for all underlayment, not just at the eaves. However two components conspire to reduce the effectiveness of felt as ice-dam protection: every nail at the eaves punctures the felt, and with age felts often dry and disintegrate before the slates have worn out.

Ice dam protection is improved in new or re-roof applications using the newer sticky membranes such as WR Grace's Ice and Water Shield^TM. However the preferred solution to this problem is proper attic ventilation. Good venting avoids the ice-dam problem and adds reductions in winter moisture and summer heat problems. Old houses whose attics have been converted to living space, particularly with un-vented ceilings following the underside of fully-insulated roofs are likely to be serious moisture and heat traps.

Slope requirements for slate roofs In conventional roofing design slates are used on roofs with a slope of at least 4" of rise in 12" of run, that is, on 4 in 12 roofs. A 3" head lap is used, often 4" when the slope is less than 8 in 12. So a 20" long slate, with a 3" head lap, would have an exposure of 8.5". For 18" slates the exposure is 7.5", and for 16" slates, 6.5". Roofs with less head lap or more exposure may be more leak-prone.

But slates have been used even on dead flat surfaces such as balconies and decks, as we show here.

When we inspected this slate covered deck in Newburgh, NY in 1991 we found that the slates had been set in a bed of tar over canvas to form a flat roof that lasted without leaking for nearly 50 years.

But as you can see in our photo, the slates had now come loose from their bed of tar.

Frequently Asked Questions (FAQs) about the importance of recognizing the history of repairs to a slate roof

...

Ask a Question or Search InspectApedia

Questions & answers or comments about assessing a slate roof condition by observing its repair history.

Ask a Question or Enter Search Terms in the InspectApedia search box just below.

Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

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

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, 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.

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
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),
...


	InspectAPedia^®	InspectAPedia
	Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair	Ask a Question or Search InspectAPedia

Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair

Ask a Question or Search InspectAPedia