Shingles in a ladder pattern and failure or leaks on a NY roof (C) Daniel Friedman Asphalt Shingles Nailed in a Ladder Pattern
Definition & effects of asphalt shingle laddering or ladder pattern installation

  • LADDERING vs STAIR STEPPING SHINGLES - CONTENTS: Ladder pattern application of asphalt roof shingles, appearance and wear issues. What is shingle laddering.Does ladder pattern shingle installation affect roof life?Definition of shingle laddering, comparing shingle laddering with standard 4" 5" or 6" shingle course offset nailing patterns.
  • POST a QUESTION or READ FAQs about the pros and cons of installing roof shingles in a ladder pattern

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 failure, leak and patch job in a pattern strongly suggestive of shingle laddering. In fact the ladder pattern installation of these shingles may be the root cause of leaks in the locations shown by the dark vertical patch areas of the roof.

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Laddering vs stair-stepping vs proper staggering of of roof shingle courses

The first photograph here 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 single six inches (or in this case only 3") left and right with each shingle course.

[Click to enlarge any image].

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

Laddered roof shingle pattern (C) J Wiley Steven BlissWhen 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. )

[Click to enlarge any image].

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.

The sketch of shingle laddering patterns shown above is adapted from Best Practices Guide to Residential Construction and discussed further below.

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. We illustrate this phenomenon in detail in the next article in this series (linked-to at the Continue Reading header at the end of this text).

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

6-inch offset asphalt shingle nailing pattern - adapted from Professional Roofing 5/2000Shingles 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 at left 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)[1] [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.

Shingle Laddering is Not Recommended

Shingle course staggering (C) Wiley and Sons, S BlissAs reported in Best Practices Guide to Residential Construction:

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

James A. Skees, PE

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 the More Reading links or topic ARTICLE INDEX shown below.

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LADDERING vs STAIR STEPPING SHINGLES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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