Definition & effects of asphalt shingle laddering or ladder pattern installation. This article series defines shingle laddering - an installation pattern, and it explains how to identify & evaluate shingles installed in this "ladder pattern". The information here describes the various sorts of roof leak, wear, and cosmetic issues caused by shingle laddering as
an example of something a bit less than the "best" roof installation workmanship. These shingle laddering defects occur on both organic-mat and fiberglass-mat
asphalt roof shingles.
Our page top photo shows an asphalt roof whose shingles were installed in the ladder pattern working up the roof rather than staggering shingle courses. The darker shingles mark areas of early roof shingle granule loss - a separate issue - whose resulting change in colour makes the ladder shingle pattern quite apparent.
Laddering vs stair-stepping vs proper staggering of of roof shingle courses
[Click to enlarge any image].
The photo just above shows a sloppy "ladder pattern" installation of strip-type asphalt shingles. While opinions (and expertise) vary
among roofers, this ladder pattern shingle application may not be as durable a roof installation as one which staggered the shingle offsets more than a
six inches (or in this case only 3") left and right with each shingle course.
Our page top photograph of shingle laddering also illustrates granule loss probably traced to specific bundles of shingles that were defective. See GRANULE LOSS from SHINGLES for more about that separate problem.
The second photograph, of fishmouthed asphalt shingles in a roof shingle ladder-nailing pattern at above-right right is courtesy of ASHI home inspector Carl Gerosa, New Rochelle, NY.
Definition of Laddering, Stair-Stepping, & Staggered Roof Shingle Courses
Definition of Laddered roof shingles
When shingles are installed on a roof using the "ladder" pattern or method, the roofer nails shingles straight up the roof, leaving the left or right shingle tab un-nailed so that when the roofer begins the next vertical assault on the roofing job he can interweave successive courses of those shingles into the ones already nailed.
(Forgetting to go back and add the missing nails is a common laddered-roof defect as Skees elaborates below. )
The laddered shingle nailing approach, not recommended by roofing manufacturers, permits the roofer to work right up the roof from eaves to ridge, without having to move beyond reach to left or right - an approach that is appealing if the roofer is working from roof jacks or other scaffolding that s/he does not want to keep relocating.
On laddered asphalt shingle roofs, particularly older ones,
you may notice that the pattern of fishmouth occurrence on an asphalt shingle roof follows a fairly regular or stair-stepped
pattern, or it may follow a regular "ladder" like pattern up the roof such as is shown in these photographs. Or as illustrated in the photo just above and in our page top photograph as well, shingles installed using the laddering pattern may become apparent as the roof ages or wears.
That's because the fishmouthing is occurring at
the butt joints of the shingles where more moisture is passing out of the roof structure into the back side of the shingle
above each butt joint.
Definition of stair-stepped roof shingle pattern:
The phrase stair-stepped shingles is usually synonymous with ladder roof shingle patterns
Definition of staggered roof shingle course nailing patterns: 4", 5" or 6" shingle course stagger nailing
Shingles are nailed to the roof deck such that each successive shingle course is offset 4", 5" or 6" thus distributing the butt joints over a wider horizontal area. This is a recommended roofing practice.
The sketch above illustrates a six-inch stagger or offset shingle nailing pattern. You can identify, even from the ground, the staggering pattern by noting that the shingle tab cutouts align every other course. This is a 6-inch stagger pattern. A four-inch shingle offset pattern will produce cutouts aligning over one another vertically every third course, while a five-inch shingle offset pattern will produce tab cutouts that align over one another every seventh course.
Sketch adapted from Flickinger (2000) [Click to enlarge any image]
You can thus determine the actual pattern in which the shingles were applied to the roof. "Laddering," while
permitted by some manufacturers and standards, is a less workmanlike shingle installation and may result in a localized early
wear area on a roof. Ladder-pattern shingle application shows that the roofer liked to work up the roof from one position for
as long as possible before moving.
Below on a re-roof job in New York you can see, even from a distance, that the roofer is applying the roof shingles in a staggered, not a ladderd, pattern.
For ease of installation some roofers install shingles
straight up the roof, staggering shingles 6 inches or
18 inches back and forth (Figure 2-9).
Since this lines up
the shingle butt joints every other course, this is considered a less watertight
roof and may leak.
Note: there is an important difference between vertical alignment of the shingle tab cutouts (a cosmetic effect described above), and the vertical alignment of shingle butt joints (the abutment of two individual shingles).
Vertically-aligned shingle butt joints that appear separated by just one shingle course are more likely to leak,especially in heavy or wind-blown rain storms.
Watch out: Installing roof shingles in a ladder pattern is not recommended
by any roofing manufacturers.
Manufacturers also claim
that shingle color patterns may create splotches or stripes
if laid this way.
A Forensic Engineer's Comments on Shingle Laddering and Asphalt Roof Shingle Wind Damage
Nail Omissions - leaving out some nails - is at fault in laddered shingle blow-offs
On the photo of the laddering problem submitted by Carl Gerosa of New Rochelle, NY: I have found that the loose corners are most often associated with the installer neglecting to place the nails at the ends of the shingles when installing the subsequent rows.
It is not necessarily the result of installing the shingles in a straight line up the roof. The same problem will occur diagonally when the nails are neglected (the common term is "three-nailing"). If the nails are all in the right place, the corners generally stay down either way.
Also see Mr. Skees' comments about nailing errors & asphalt shingle cellophane strip removal at WIND DAMAGE to ROOFS
Continue reading at LADDERED SHINGLE FAILURES & WEAR or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
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 Dave Flickinger, "Offset Patterns for Asphalt Shingles", Professional Roofing, National Roofing Contractor's Association (NRCA), May 2000. Professional Roofing Magazine, 10255 W. Higgins Rd., Suite 600, Rosemont IL 60018, Tel: 847-299-1183.
Carl Gerosa, Target Inspection Consultants, Inc., New Rochelle, NY 10804, Tel: 914-833-2900 / 914-834-7494, New York Home Inspectors License Number: NY 1600005625/CT 20 is a certified ASHI inspector and a member of CAHI, the Connecticut Association of Home Inspectors. Mr. Gerosa provides home inspections of Single Family Homes, Radon Testing, Wood Destroying Organisms. Email: email@example.com
Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
Arlene Puentes, a licensed home inspector, educator, and building failures researcher in Kingston, NY
Thanks to James A. Skees, PE, President and Sr. Forensic Engineer, OnTheRock Engineering, LLC, 604 W. Jefferson Street, LaGrange, KY 40031
502-225-6203 FAX 225-6204, for commenting on the roof cellophane strip problem, on wind damage to roof shingles, shingle blow off, improper shingle nailing, and roof shingle laddering underlying defects, August 2010. Mr. Skees is a forensic engineer who works for insurance companies. Mr. Skees can also be reached by email at firstname.lastname@example.org
The company has published online a sample Tornado Report
"Residential Wind Damage Evaluation", Wind Damage Sample, found at http://www.ontherockeng.com/Sample%20Tornado%20Report.pdf
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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
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).
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.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 extensive home inspection education and report writing material.
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.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
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.
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 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