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• Asphalt roof shingle fishmouthing, photographs, cause, prevention
• Types & photographs of organic felt asphalt roof shingle defects & failures

This website tells readers how to identify & explain the asphalt shingle roof wear pattern known as "fishmouthing" or "fishmouthed roof shingles". We discuss the failure pattern, its cause, its evaluation as a sign of roof wear and other problems, and how to prevent this condition. These defects occur on organic-mat or fiberglass-mat asphalt roof shingles. Common shingle failure factors include improper storage and handling of the asphalt shingles before installation, improper nailing, improper flashing (which pertains to any roofing material), and defective asphalt shingle product material leading to thermal splitting, cracking, blistering, staining, and in some cases curling or cupping shingles. Storm damage from wind and hail occur and need to be distinguished from defective asphalt shingle product or asphalt shingle installation errors. By listing common causes of asphalt roof shingle failures and how to recognize them, building owners and roofing contractors may also be able to reduce the occurrence of asphalt roof shingle storage, handling, and installation errors that affect roof life. Readers are also invited contribute roof failure information to the web author for research purposes. web author for research purposes. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

Fishmouthing Asphalt Shingle Explanation & Photos

Fishmouthed roof shingles wear in the unique raised "mouth" shape shown in photographs on this page. Just as in the case of other shingle cupping or curling patterns, this raised portion of the shingle is vulnerable to damage from foot traffic, but unlike the other cupping or curling patterns, fishmouthed roof shingles are not simply an age or wear indicator on the roof. They indicate a combination of roof moisture and a roof ventilation defects.

An example of the less-than-fully-waterproof back of asphalt roof shingles is seen in our photos of "fishmouthed" roof shingles. In these cases a specific "curling" pattern of shingles called "fishmouthing" displays a raised shingle edge which looks alot like a fish's open mouth. These shingles are not curled over at the very edge.

The location of fishmouths on roof shingles is predictable and diagnostic: if inspected closely the shingles whill show thgat this pattern of raised open lower shingle edges will occur first and worst over the shingle butt joints where individual shingle sides abut one another. So the pattern of "fishmouths" on the roof may be regular, following a diagnoal or a ladder pattern depending on how the shingles were nailed on the roof. In the photo above, you can see even from the ground that the shingles were "laddered" onto the roof rather than being staggered in a stairstep pattern when they were installed!

Inadequate Venting and High Building Moisture Cause of Asphalt Shingle Fishmouthing

Fishmouthed cupping of asphalt roof shingles is caused by excessive under-roof moisture such as by a poorly or un-vented attic or roof cavity. Moisture escaping through the roof sheathing and up through the bottom of the shingles contacts the uppermost shingle which spans the butt joint of shingles below, placing more moisture at that point on the shingle tab than elsewhere. This uneven moisture, probably combined with weather exposure, leads to a raised, cupped "fishmouth" look on those shingles.

Shingles are not quite waterproof: You may not realize it but asphalt roof shingles are not quite waterproof and in particular the back side of asphalt shingles is much less water resistant than the upper or exposed side. The exposed side of an asphalt shingle is protected from sun damage by a coating of mineral granules. These shingles rely on the pitch of the roof and mechanical drainage combined with proper placement or pattern of shingling on the roof to avoid leaks. [This photo courtesy of Carl Gerosa, New Rochelle, NY.]

Shingle Fishmouthing is a Building Diagnostic Aid

I took this photograph of fish mouthed roof shingles as a great example of how they diagnose other building conditions. This was a car wash - talk about a lot of interior moisture in a building! There was also no roof venting system of any consequence on the building. So fishmouthed roof shingles mean that there has been a combination of high interior building moisture, (maybe from a wet basement or a flood?) combined with poor or inadequate under-roof ventilation. Unlike other more normal wear patterns on asphalt roofs, such as curling, cupping, or even some cracking or granle loss patterns, fishmouthing tells us something more about the building itself and its leak, moisture, and venting history and design.

Fishmouthed Asphalt Roof Shingles under light snow cover - an Ice Dam, Leak, Mold, Rot Warnings

Because the raised "fishmouths" on asphalt shingles show up above and through a light snow cover, this is one roof pattern, wear indicator, and sign of both moisture and bad roof venting design that you might be able to diagnose from the ground under some conditions. This is an important condition to notice because the same inadequate under-roof venting that was a factor in the creation of these fishmouths on the roof surface may also have led to ice dam problems on the same building. In turn, ice dams may have led to leaks into attics, ceilings, or building walls. In turn, leaks into building walls might have led to a hidden mold problem on the buildng. So those fishmouthed shingles might actually be a fair predictor of mold problems on some buildings and if other factors or complaints are present, might be a reason to explore the building wall cavities under the roof eaves, looking for evidence of leaks, mold, rot, or insect damage where otherwise we might not feel that such invasive measures were justified.

Fishmouthed Asphalt Shingles are Vulnerable to Damage

As I suggested in the cased of other cupped, curled, or fragile asphalt roof surfaces, I would stay off of fishmouthed-shingle roofs, particularly in cold weather (when the fishmouthed roof shingles are more likely to break). If we have to walk on a fishmouthed shingle roof, tiptoe carefully, avoiding stepping on the raised or fishmouthed shingle sections.

Do Fishmouthed Asphalt Shingles Need Replacement?

If the shingles are not damaged, broken, cracked, or showing other signs of wear, it may be possible to leave these shingles on the roof longer than otherwise. That's because this fishmouth pattern can show up earlier in shingle life on a wet building with poor under-roof venting. An experienced inspector or roofer can point out the extent of roof damage and other shingle wear signs that will decide if the roof is ready to be replaced.

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Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• 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. (727) 595-4211 mark@BestTampaInspector.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.
• Daniel Friedman - principal author
• Technical reviewers are invited to comment or ask questions - contact us

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