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This slate roofing photo library shows various kinds of roofing slate defects. This photographic dictionary of roofing slates is a supplement to our detailed article (links at page left) describing procedures for evaluating the condition of slate roofing. The main article reviews types of slate, common defects, inspection topics, and some repair tips. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

This article assists home inspectors, building buyers or building owners, and roofing contractors in evaluating the condition of slate roofs by providing photos of various slate materials, patterns, defects, and conditions. Readers should also see How to Inspect & Repair Slate Roofs for a detailed "how to" article on inspecting, evaluating, and repairing slate roofs.

A Photographic Guide to Defects in Slate Roofs

Photo guide to Cracked, Broken Slate Roofing Inspection & Repair

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  Cracked, broken slates, probably not leaking but note the diagonal crack in the slate below the course with a missing slate half
  
  
  
  
  
  
  
  
  
  
  
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  Cracks: Slate crack repair, copper was slipped up over a slate which had split just below the butt joint of slates in the next course
  
  
  
  
  
  
  
  
  

Photo Guide to Delaminating Roofing Slates

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  Delaminating roofing slate, if the delamination is only in the upper surface layer of the slate the material may have substantial remaining life.
  
  
  Also ask how many of the roof slates are delaminating at all - note the neighboring slates on this roof are sound.
  
  
  
  
  
  
  
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  Surface delamination on slates: Notice the surface delamination on some of these slates. A close inspection is needed to evaluate slate delamination when it looks like this. We need to know if the slate is basically sound, hard, and secured to roof, or if alternatively the delaminations are throughout the slate body, making it soft.
  
  See our photos at SOFT DETERIORATED SLATES where we show close up photos of slate that looked pretty good on the roof but when touched, disintegrated easily
  
  
  
  
  

Photo Guide to Slate Roof Flashing Details

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  Flashing: Chimney in the roof valley, was a probable factor in recurrent leaks in this slate roof
  
  
  
  
  
  
  
  
  
  
  
  
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  Flashing: Slate roof with good side-wall step flashing, against a brick wall
  
  
  
  
  
  
  
  
  
  
  
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  Flashing: Suspect copper valley in slate roof, note the attempt to "patch" the valley with roof mastic - and the cracks in the mastic - this repair is not durable

Photo Guide to Loose, Sliding, Lost Roofing Slates & Slate Nails 

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  Nails: sliding slates, mean the nails are lost - perhaps from corrosion.
  
  Don't underestimate the implication of many slates which have moved only a little bit - all may have lost their nails.
  
  Notice also the surface delamination on some of these slates.
  
  
  
  
  
  
  
  
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  Nails: Slate fastener failure, might be indicated by the slate at right if it is sliding down - can you move it back up?
  
  If you can, this slate has lost its nail and is not connected. Use a slate hook or copper tab to secure the loose slate in place.
  
  
  
  
  
  
  
  
  
  
  
  
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  Nails: Roof Tiles (not slate), repaired using copper strips - the strip ends holding tiles have been bent back by sliding snow - expect movement, leaks, and extensive nail failures.
  
  This defect also occurs on slate roofs repaired using this method. This demonstrates the advantages of slate hooks in lieu of copper strips when replacing lost slates.
  
  
  
  
  
  
  

Slate damage at chimney and lower edge, probable leaks at chimney. Why to the slates seem loose particularly around the chimney?

Often the building framing settles away from the masonry chimney as framing ages, sags, or settles due to shrinkage or later rot or other in-building damage. But the chimney, built of masonry, tends to remain the same height.

On many old houses the framers actually connected roof framing right to the chimney. Later when the building sagged, settled, or moved, the framing pulls away from the chimney causing damage to the roofing slates and flashing, and leading to leaks in this area.

Another common source of slate roof damage around a chimney is wear and movement caused by flashing leaks and, in freezing climates, frost.

Photo Guide to Slate Roof Defects: Mineral Inclusions & Staining in Slates

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  Mineral inclusions: Slates with mineral inclusions, the wash-out of minerals in some slates can lead to holes and leaks
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Mineral inclusions, holes in slates - the slates with these defects need to be replaced or patched from below with copper panels.
  
  
  
  
  
  
  
  
  

Stains and Wear Indicators on Slate Roofing, a Photo Guide

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  Staining on roofing slates: Slate edges showing moisture absorption, but generally good condition, these slates have a good remaining life
  
  
  
  
  
  
  
  
  
  
  
  
  
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  White Efflorescence on roofing slates: the white markings shown on these roofing slates, is a mineral deposit left behind as water evaporates. Water penetrating the slate material absorbs minerals and leaves some of them, probably Ca and Mg on the slate surface.
  
  Many slate roofers and slate inspectors assert that as the white stains progress from the edges of individual slates towards their center, one can estimate the remaining roof life. If 50% of the slate remains inside of the white area, the slate may have about half of its life remaining.
  
  We recommend that this condition be confirmed by close inspection as well since other slate deterioration factors could be at work.

Thickness of Roofing Slates, Close up Photo of Slate Edges in Good Condition

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  Slate edge close up, showing the natural layering of mineral deposits in the original stone
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Thickness: Measuring slate thickness, and close up inspection permits check for slate delaminating and softness
  
  
  
  
  
  
  
  
  
  
  
  
  
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  Thin, worn slates, French and conventional pattern, missing slates, tar patches, leaks. This roof is probably repairable But we 'd need a closer look at those slates to evaluate their thickness and hardness.
  
  
  
  
  
  
  
  
  

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More Information on Building Diagnostic Inspections and Repairs

Slate Roofing References

• 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.
• 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

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