Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
ROOFING INSPECTION & REPAIR
AMERICAN CEMWOOD ROOFING
BEST ROOFING PRACTICES
BUILT UP ROOFS
CATHEDRAL CEILING VENTILATION
CERTIFICATIONS for ROOFING CONTRACTORS
CHIMNEY FLASHING Mistakes & Leaks
COLD WEATHER ROOF TROUBLE
DECKS, ROOFTOP CONSTRUCTION
EPDM, RUBBER, PVC ROOFING
EXTRACTIVE BLEEDING on SHINGLES
FIRE RETARDANT PLYWOOD
FLASHING on BUILDINGS
FLASHING, ASPHALT SHINGLE VALLEYS
FLASHING, CHIMNEY Mistakes & Leaks
FLASHING, CLAY TILE ROOFS
FLASHING MEMBRANES PEEL & STICK
FLASHING for METAL ROOFS
FLASHING ROOF WALL DETAILS
FLASHING ROOF-WALL SNAFU
FLASHING SIDING DETAILS
FLASHING WALL DETAILS
FLASHING WINDOW DETAILS
FLASHING WOOD ROOF DETAILS
FLAT ROOF MOISTURE & CONDENSATION
Green House or Solarium Roof Leaks
HEAT TAPES & CABLES for ROOF ICE DAMS
ROOF ICE DAM LEAKSbr />
MASONITE WOODRUF FIBERBOARD ROOFING
NOISE CONTROL for ROOFS
PLASTIC ROOFING TYPES
PVC, EPDM, RUBBER ROOFING
ROOF ARCHITECTURAL STYLES - PHOTO GUIDE
ROOF CLEANING RECOMMENDATIONS
ROOF COLOR RECOMMENDATIONS
ROOF DORMER TYPES - PHOTO GUIDE
ROOF INSPECTION SAFETY & LIMITS
ROOF JOB PROBLEMS, RESOLVING
ROOF LEAK DIAGNOSIS & REPAIR
ROOF NOISE TRANSMISSION
ROOF REPLACEMENT SNAFUs
ROOFING FELT UNDERLAYMENT REQUIREMENTS
ROOFING MATERIALS, Age, Types
ROOFING TILE SHAPES & PROFILES
ROOFING UNDERLAYMENT BEST PRACTICES
SADDLE CONSTRUCTION at CHIMNEYS
SNOW GUARDS & SNOW BRAKES
STANDARDS for ROOFING
STRESS SKIN INSULATED PANELS
TEST LABS - ROOF SHINGLE
TREES & SHRUBS, TRIM OFF BUILDING
TRUSSES, Floor & Roof
UNDERLAYMENT REQUIREMENTS on ROOFS
VENTILATION in BUILDINGS
WALK-ON ROOF SURFACES
WARRANTIES for ROOF SHINGLES
WORKMANSHIP & ROOF DAMAGE
Asphalt shingle laddering wear & failure patterns: this article describes the wear, leak, or failure patterns seen on asphalt shingle roofs that were installed in a ladder-pattern. Some, but not all of these wear conditions can be ascribed to the ladder-pattern of installation. In other photos the ladder pattern-marked shingle wear tells us something else about why the roof is wearing early or unevenly.
This article series describes the installation of asphalt roof shingles in a ladder-approach rather than a multi-course staggered approach to nailing shingles and illustrates the effects of this method on roofs. Our page top photo shows asphalt roof shingles that were installed in the ladder pattern - made very apparent by the early wear and failure of some of areas of the roof - a wear condition that we explain in the text below.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
At left is a closer view of the wearing shingles on the asphalt shingle roof shown at page top. The dark shingles in the photo center and lower right show granule loss - early wear or product failure whose cause we can guess.
[Click to enlarge any image]
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.
Getting back to the asphalt shingle ladder pattern photo show just above, I've marked and numbered four roof areas on this slope of a roof pointed out by my daughter Michelle Friedman and found in Haddonfield, New Jersey. Here is some experienced, informed speculation about four conditions seen on this roof:
Shingle Cracking or Thermal Splitting at Roof Locations Determined by Shingle Installation Pattern
At left you can see long vertical lines of black roofing mastic or sealant that was applied to try to seal cracks or tears in these asphalt roof shingles observed by looking down from the Poughkeepsie NY railroad bridge.
Thermal splitting, cracking, or tearing is an asphalt shingle manufacturing defect discussed in detail at CRACKS in FIBERGLASS SHINGLES.
There we explain that thermal splitting occurs in asphalt roof shingles made without adequate tear resistance, especially when combined with very effective self-sealing shingle tabs (intended to protect against wind-blow-off) and combined again with thermal movement that is more pronounced in areas subject to both freezing winters and hot summers.
Some inspectors opined that the crack pattern on this roof maps 8-foot lengths of roof plywood. Balderdash! You can see thermal splitting occurring in vertical patterns that range in width from one shingle to several individual shingle widths on the roof.
On the roof roof shown above the installation of shingles in a ladder pattern did not cause the thermal splitting problem, but it explains why the thermal splits occur in long vertical lines in the pattern seen in the photograph.
[Click to enlarge any image].
Shown for comparison, at left I include a photograph of thermal splitting occurring along a diagonal on a different roof. These shingles were installed in a standard half-tab offset staggered pattern up the roof rather than in a ladder pattern.
The result is that butt joints march on a diagonal up the roof, and so does thermal splitting in the tabs placed over those butt joints.
While thermal splitting can indeed run vertically up any asphalt shingle roof, why are these shingles splitting along these particular and parallel and long vertical lines? Probably because the ladder pattern creates a vertical line of shingle butt joints that run straight up the roof on alternating shingle courses.
Shingle Fishmouthing Occurring in Patterns Mapped to Shingle Ladder Pattern Installation
At below left you can see shingle fishmouthing, a characteristic upwards curved "mouth" occurring roughly in parallel vertical runs up the roof. Click to enlarge the image and you'll see even more interesting evidence. Alternating courses of shingles are producing a fishmouth that is almost exactly 1/2 shingle tab offset from the fishmouthing occurring in shingle courses just above and below.
This pattern of occurrence of fishmouthing is almost certainly mapping the butt joints (below each raised fish mouth) of shingles installed in a shingle ladder installation pattern - shingles installed lapped 1/2 tab to the left, then right, as the roofer worked straight up the roof slope.
Just to illustrate and prove the shingle laddering-fishmouth claim for the roof at above left, in my photo at above right we illustrate fishmouthing occurring on long diagonals on another 3-tab asphalt shingle roof. These shingles were nailed in the more conventional roof shingle nailing pattern in which shingle courses were offset by 1/2 tab working to the roofer's left or right for six shingle courses at a time.
This increased staggering shows up as follows: choose any fishmouth on the roof and count up-slope until you find another one directly above it. You'll get to six - the number of shingle courses that were nailed in a staggered offset before any shingle butt joint appears over a shingle course below.
Why six? Each of these shingles is comprised of 3 individual tabs separated by slots. The roofer offsets each successive shingle course 1/2 of a tab (about 6 inches) to the left (or right if she is working to her right) as courses are nailed onto the roof. Do the math - you'll see that offsetting 1/2 a tab at each course will run 6 courses before the pattern repeats.
Fishmouthing is most likely caused by a greater concentration of moisture entering the under-side of an asphalt shingle from below, perhaps from a damp attic or one with excessive moisture condensation. Where shingle butt joints occur the tab overlying the butt joint will receive more moisture (up through the butt joint gap) than neighboring shingle tabs that are not placed over a shingle butt joint.
Continue reading at LADDERING vs STAIR STEPPING SHINGLES or select a topic from the More Reading links shown below.
Suggested citation for this web page
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References