Roof Leaks: diagnosis & repair guide
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What are the different types of roof leaks and how do they help us diagnose the cause of roof leaking?
How to repair leaky roofs
How to determine if a roof leak is active or old, inactive, previously fixed
How to track wet areas under roofs or ceilings back to the actual leak source
Does a roof leak mean that I need an entire new roof?
How to decide between repairing a roof leak and replacing the whole roof
Questions & Answers diagnosing & repairing leaky roofs

This article describes procedures for finding and fixing all types of leaks in roofs, figuring out the actual spot where a roof leak is occurring, and methods for tracking down the source of water or wet spots on ceilings or in attics.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers nor with topics or services discussed at this website.

The first part of this article describes different types and causes of roof leaks - clues about how and where to look for the causes of a roof leak. The second part of this article discusses how we track an actual roof leak backwards to its probable source or entry point on the roof.

This article series helps with diagnosis and repair of roof leaks found in different types of roof coverings and different types of roof designs. We distinguish among actual roof leaks during rainfall, unusual leaks during hurricanes and high winds, wind-blown rain leaks, ice dam leaks in northern climates, and attic condensation or HVAC ductwork condensation and icing that may be mistaken for a roof leak in any climate.

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How to diagnose and repair Leaky Roofs

Types & Classes of Roof Leaks

This list of different sorts of building leaks can help diagnose the cause and location of what seems to be a leaky building roof and thus can guide the roof leak repair process to a successful end.

Roof leaks caused by roofing material wear or normal aging

This category includes wearing out of roof covering materials (shingles, slates, membranes) and corrosion or rusting through of roof flashings or sealants.

All roofing materials and coverings can be expected to age and wear with the passage of time and particularly with exposure to sun and various weather conditions.

But different roofing materials wear at different rates (SLATE ROOFS, for example should last longer than ASPHALT ROOF SHINGLES), and even within a particular roof material class, such as asphalt shingles, roof wear and roof life will vary as a function of other factors such as roof slope, color, direction of weather exposure, and local climate (exposure to salt, sun, etc.). At page left you'll see articles for each type of roofing and in those you'll find details about the life expectancy of that material.

See these articles describing the wear and aging factors on roofs in more detail:

ASPHALT SHINGLE LIFE / WEAR FACTORS. There, in an argument similar to the observation that two people born on the same day may age and look very differently decades later, we discuss the difference between the chronological age of a roof covering and it's "wear age". Also see ASPHALT SHINGLE FAILURE TYPES.
AGE OF ROOFING assists in determining the age (era of use) and style of roofs and roof coverings.
EARLY ROOF FAILURE DIAGNOSTIC QUESTIONS
At page left you'll see articles for each type of roofing and in those you'll find details about the life expectancy of that material. Here are just a few examples of articles that distinguish types of roof wear:
- Wear Signs on Cement Asbestos Shingles discusses indications of wear on asbestos-cement roof shingles
- CUPPING ASPHALT SHINGLES and CURLING ASPHALT SHINGLES might be normal wear indicators on an asphalt shingle roof, while a different shingle curling pattern, FISHMOUTHING ASPHALT SHINGLES, may indicate poor under-roof ventilation and/or high in-building moisture levels or both

Roof leaks caused by events: storm damage, falling tree limbs, walking-on, chopping ice, high winds, other unusual events

Of the roof leaks caused by events, such as those listed above, one could further separate leaks as caused by act of god or nature (unusual storms and wind or wind-blown tree branch or object damage to roofs) from leaks caused by human error (chopping ice or shoveling snow off of roofs using methods that damage the roof shingles). See

CLAY TILE WIND & SEISMIC CONNECTORS - describes special connections recommended for clay tile roofs in high wind areas. Similar specifications are provided under other individual roof material types listed at page left.
HAIL DAMAGED SHINGLES - scouring of mineral-granule protected roof surfaces such as asphalt shingles removes the protective granules and can lead to reduced roof shingle life
WALK-ON ROOF SURFACES - yes it's possible to install roofing that is able to tolerate foot traffic
Windstorm Damage Prevention - high winds, hurricanes, tornados can damage roofs even when properly installed; in areas subject to frequent high winds, special roof fastening requirements are listed.
Wildfire Damage Prevention - special fire-resistant roof coverings are required in areas prone to wildfires and forest fires or similar fire risks

Roof leaks caused by poor original installation or workmanship

Examples of workmanship-related roof leaks or poor installation of roofing include:

Roof flashing mistakes: Leaks at improperly installed or even omitted roof flashings anywhere (roof penetrations at plumbing vents, chimneys, or bath / kitchen vents, improper roof-to-sidewall flashing, improper or inadequate roof valley flashing. See these roof flashing articles to look for examples of foul-ups that can produce roof leaks at flashings:
- ROOF FLASHING DEFECTS LIST
  
  FLASHING, ASPHALT SHINGLE VALLEYS
  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 WOOD ROOF DETAILS
  Chimney Flashing Mistakes & Leaks
- SADDLE CONSTRUCTION at CHIMNEYS
Improper roof gutter installation, can sometimes cause or contribute to debris back-up at roof edges, gutter overflows or back-flows down building walls, and even leaks into building soffits or eaves that may be blamed on a leak in the roof surface
Improper roof shingle nailing, such as improperly placed nails or inadequate nails, leading to shingle wind-blow-off
Improper roof shingle placement, such as inadequate offset between abutting roof shingles in roof shingle courses (rows of shingles marching up the roof) can lead to leaks at butt joints; also inadequate shingle exposure - spacing courses (rows) of roof shingles too far apart up the roof can lead to leaks at shingle butt joints.
Inadequate under-roof ventilation on some structures can lead to reduced shingle or roof covering life due to either higher roof surface temperatures or higher under-roof moisture, both of which could have been reduced or avoided by ventilation. See
- ATTIC VENTILATION - recommendations, designs, specifications, alternative methods
- CATHEDRAL CEILING VENTILATION - how to vent cathedral ceilings
- HOT ROOF DESIGNS: Un-Vented Roof Solutions for roofs where it's difficult or impossible to provide ventilation.
- HEAT TAPES & CABLES on Roofs for Ice Dams - does this stop gap method work?
- HUMIDITY LEVEL TARGET - are some buildings just too damp?
- ICE DAM PREVENTION - how to avoid ice dam leaks on roofs
- ROOF VENTILATION SPECIFICATIONS - home page for roof ventilation specs, designs, requirements
Layers of roofing material, too many - reduces roof life, can trap moisture, and can make tracing roof leaks extra difficult. See ASPHALT SHINGLE RE-ROOF GUIDE for a discussion of roof surface preparation for re-roofing and the number of roof layers permitted.
Additional articles on roof installation workmanship problems
- CHOOSING A ROOFING CONTRACTOR - avoid roof troubles by choosing your roofer with care
- DISPUTE RESOLUTION on ROOF JOB PROBLEMS - how to resolve roofing issues with your contractor
- FELT UNDERLAYMENT REQUIREMENTS and ROOFING UNDERLAYMENT BEST PRACTICES - is roofing felt or underlayment required?
- WORKMANSHIP & ROOF DAMAGE for details about roof leaks and wear traced to poor workmanship an

Roof leaks due to inadequate or improper roof maintenance

Examples of maintenance-related leaks in or through building roofs include

Clogged roof drains or roof drain scuppers on flat or low slope roofs; the result of clogged low slope or flat roof drainage is water backup that can cause leaks through a roofing membrane that relied on slope and mechanical gravity, leaks at seams in very low slope or flat roofs, and catastrophic leaks through burst or damaged roof drains that pass through the building itself.
Walking on fragile roof surfaces: asphalt shingle roofs or fragile roll roofing, or just about any other old, worn, or innately fragile roofing materials (clay tiles, slate roofs, older wood shingle roofs, curling old asphalt shingle roofs) is likely to damage or break the roofing material, leading to leaks.
Failure to inspect and maintain roofs & seams on flat and very low slope roofing
See
- Debris Staining on Roofs - identify & remove debris from roofs
- GRANULE LOSS from SHINGLES - might be due to normal roofing wear on asphalt surfaces, or it might be due to heavy-footed workers tramping over the roof, especially in hot weather.
- GUTTERS & DOWNSPOUTS - keep roof drainage system working
- LOW SLOPE ROOFING - inspect and maintain low slope and flat roofs, seams, drainage
- MECHANICAL DAMAGE of SHINGLES - cut or broken shingles due to heavy-handed ice-chopping or tearing during other work
- ROOF CLEANING RECOMMENDATIONS - clean debris from roofs
- TREES & SHRUBS, TRIM OFF BUILDING - keep trees trimmed back off of roof surfaces

Roof leaks caused by use of defective roofing product

We divide "defective roofing product" into two categories: roof materials that were defective when they left the production facility, perhaps due to a process control error or a problematic product design, and roof materials that were defective due to improper storage before installation on a roof. See:

BLISTERS on ASPHALT SHINGLES - are considered just a cosmetic defect according to roofing manufacturers; we're not sure that's always the case.
CRACKS in FIBERGLASS SHINGLES provides examples of defective asphalt shingles failing due to thermal splitting
MASONITE WOODRUF FIBERBOARD ROOFING
RIBBON SLATE - some ribbon slates are long lasting, others were of less durability due to soft mineral inclusions
TEST LABS - ROOF SHINGLE - where to obtain independent testing of suspect or failed roofing materials
WARRANTIES for ROOF SHINGLES - advice on obtaining warranty service for failed roofing products

Roof leaks that aren't - indoor moisture, stains, water, leaks mistaken for roof leaks.

These false roof leaks can cause waste of time and money as well as aggravating disputes between building owners, roofing contractors, and other building contracting and repair companies. Some examples include:

Unusual wind and rain or wind-blown rain direction that blows rain into a building attic through a ridge vent, soffit vents, or gable end vents.
Attic condensation caused by inadequate attic ventilation can leave ice or frost formation on the under-side of roof decking, stains on roof decks even when the roof looks dry later on, drip stains on attic flooring, and even wet building insulation or ceilings below leading to mold contamination and water staining.
See
- ATTIC LEAKS, CONDENSATION & MOLD - a series of articles that helps distinguish between a roof leak from outside water and drip stains or mold due to in-building or under-roof condensation.

Tracking Down Roof Leaks to Their Source

It may seem obvious to say "start by looking at where you see water leaking into the building", but that is often just not enough to track a roof leak back to its source. Our low slope roof photos shown here give examples of hard-to-spot roof leak sources as well as hidden roof leak damage: rot or insect damage. Our photo (left, courtesy Galow Homes) shows a small dirt stain marking a small ponding area exactly above what we later discovered was a long-standing roof leak in an EPDM roof.

Roof leak water can move sideways: Water leaking through roof coverings travels, horizontally as well as vertically (down) the roof slope.
Roof leak water can move great distances: Water leaking into a flat or very low slope roof can travel considerable distances before it appears in the building interior. The lower the roof slope the greater the distance that water from a roof leak may travel before it shows up indoors.
Roof leak water may leave "dry" footprints: water from roof leaks falling on to an attic floor or into a ceiling may flow to a lower point at which it enters the building and is noticed; but when you inspect in the attic, especially if time has passed since the storm that sent the water through the roof, there may be a dry space between what's wet now and the actual point of water entry. At least for repetitive leaks and old leaks, stains and discolored materials may mark the water pathway even if they are dry at the time of inspection.

Our roof leak stain photo (left) shows the wall cavity immediately below the roof area I was pointing out in the roof leak photo above. As further demolition showed, the carpenter ants were having a fiesta in the wall cavity and along the top plate of this home.

Old as well as current roof leaks leave stains that remain and can confuse the process of tracking down current leaks
Check first the more obvious leak points: missing flashing, cuts, tears, holes, open seams, but watch for surprises
Surprise roof leak points are common: Having a lot of experience with building renovation, demolition, and re-roofing gives opportunities to tear older buildings apart. That, in turn, gives a real education on how, where, and why roof leaks travel where they do through buildings.

Following roof leaks to their source

We start at the point where water or stains are visible in the structure.
Map the entire wet area, using pencil marks on ceilings, moisture meters, infra-red.

Watch out: your sense of touch is not a completely reliable indicator of where water has been.
Watch out: moisture meters and infra red cameras (thermography) are great tools for tracking down moisture if they are used while things are still wet. Once a leaked-into area has partially or fully dried, those tools will not be reliable indicators of building leaks. Also, moisture meters vary in the depth to which they are able to probe building cavities for moisture. And thermography or infra red devices, relying on temperature differences, can confuse a novice who may mistake a cool area due to missing insulation with a cool area due to wet conditions.
We look horizontally as well as "up-slope" from the point where water is observed in the building to make a guess at the most likely points of water entry.
We inspect the on-roof surface for even the most tiny flaw or anomaly that might be a point of water entry at, near, or above that likely water entry point.
Roof test for leaks: We may use a garden hose, where it's practical, to flow water on or even spray water at a suspected roof leak point.

Watch out: don't use high pressure water sprays that may damage roofing, or that blow water into or through otherwise perfectly-waterproof roof designs; and of course we generally don't spray water at suspect roof areas when there is no visual access to the roof area from below.
We seal or repair suspect water entry or leak points and where it's practical we repeat our water test

How to Decide if a Roof Leak is Active or Old, How to Handle Wet Moldy Areas Discovered in a Ceiling

Question: How do I track down roof leaks and decide if leaks are active or inactive? Wet spots & black mold found during interior repairs after prior roof leaks and a new roof installation

We live in a condo building, four story, concrete structure with brick face.

We have had our flat, concrete roof repaired multiple times in the past few years. Last year the roof was sponge-y with water. We had repairs made in all areas as per a building inspector's advice, and a water expert's advice, except for some tuck pointing problems which were terribly expensive, and didn't look all that problematic . Also we installed roof vents.

This summer the roof is no longer sponge-y. It is solid. But the owners of the fourth (top) floor apartment are having interior work done and are discovering black mold and water/moisture coming in in the very areas they want to repair.

The roof LOOKS good, flashing and parapets are tight, caps on parapets are repaired and in good shape, roof surface (modified bitumen) has been sealed this summer and looks to be in good shape.

Is it possible this is still water percolating down from our concrete roof? Or should we be looking for new leaks?

Should we be calling yet another roofer? Or should we be waiting for the interior to be free of the old buildup of water which is still making its way down from the soggy, sponge-y roof we had last summer.

Thank you for any advice you can give us. - M.J.

Reply: Look for & trace moisture or water under the roof, explore for leaks during mold cleanup, don't look just for "black mold"

Follow the water pattern and moisture levels to track down flat roof leaks

If your roof is low slope or flat water travels and it can be tricky tracking down a leak - an inspector using infra red and moisture meters should be able to help sort out the question of whether there is an active leak and if so where it originates. As you report that the top floor occupant has found wet areas, it seems likely that other than concrete and structural members, other wet materials such as insulation will need to be removed - a step that will help trace the size and pattern of wet areas back to inspection points on the roof above.

Roofing over wet materials can lead to further trouble

It's common on large commercial buildings and apartments to simply add another layer of roofing over leaky flat or low-slope roofs. Sometimes the roofer will also put down a layer of insulating board first. As long as the roof can be mechanically secured soundly to the structure, that practice is acceptable in many communities.

But roofing over wet layers of old material can lead to future troubles including

moisture vapor bubble formation and bulging in the new roof membrane
difficulty distinguishing between old leaks and new leaks in the roofing system
continued mold growth in building materials and over longer periods, increased risk of rot or insect damage to wood structures

If the roofer roofed over wet conditions they could take a long time to dry out, particularly if the roof was installed atop multiple layers of old material. You didn't say how long ago the new roof was installed nor whether or not there was a tear-off of old layers. Also, while we like modified bitumen as a roof covering material, the roof can "look good" but could have improperly made seams.

An experienced roofer or roof inspector will look closely at the modified bitumen seams and flashing details to be more confident that at least from above the roof doesn't show obvious leak points. See MODIFIED BITUMEN ROOFING for details.

Mold Under Leaky Roofs - some basic advice

Mold that was discovered by the top floor occupants may have been pre-existing due to the previous leakage; that's particularly likely given that there were prior roof leaks. Further inspection to identify the extent of mold cleanup needed as well as the source of leakage should be a natural part of mold cleanup. No mold cleanup job would be complete without finding and fixing any remaining building leaks, and no renovation job would be well done if it simply covered-over a problematic mold contamination.

Focus on "black mold" is a mistake. There are many genera/species of harmful mold, only some of which are dark in color. The "black molds" are easier to see so may be over-reported. It would be unlikely that only one genera/species of mold is present in a leaky building, but often lighter colored mold contamination is harder to see, even if it is equally or even more of a potential health concern.

Leaky masonry walls remain on your project - watch out for rain and storm damage such as from Hurricane Irene

Watch out: wind-blown rain, particularly during storms such as Hurricane Irene that brought long durations of high winds and heavy rainfall, can penetrate masonry buildings through walls and roof parapets. These masonry wall leaks may be mistaken for roof leaks when they begin high on the building walls.

We understand the wish to postpone very costly building repairs, not to mention the worry that the costly repairs may not be done properly, leading to still more costs. But depending on the materials used and structure of the building walls, leaks into wall cavities can cause such costly damage that it is almost always justified to properly seal the building exterior against storm driven rain leaks.

These InspectAPedia articles may be helpful:

LEAKY ROOF DIAGNOSIS & REPAIR
MODIFIED BITUMEN ROOFING
MEMBRANE & SINGLE PLY ROOFS
FLAT ROOF MOISTURE & CONDENSATION

HIDDEN MOLD, HOW TO FIND
MOLD AGE - Old is the Mold?
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE

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Questions & Answers diagnosing & repairing leaky roofs

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LEAKY ROOF DIAGNOSIS & REPAIR

Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Eric Galow, Galow Homes, Lagrangeville, NY. Mr. Galow can be reached by email: ericgalow@gmail.com or by telephone: 914-474-6613. Mr. Galow specializes in residential construction including both new homes and repairs, renovations, and additions.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book 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. InspectAPedia.com ^® editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
The Journal of Light Construction has generously given reprint permission to InspectAPedia.com for certain articles found at this website. All rights and contents to those materials are ©Journal of Light Construction and may not be reproduced in any form.
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How to diagnose and repair Leaky Roofs

Types & Classes of Roof Leaks

Roof leaks caused by roofing material wear or normal aging

Roof leaks caused by events: storm damage, falling tree limbs, walking-on, chopping ice, high winds, other unusual events

Roof leaks caused by poor original installation or workmanship

Roof leaks due to inadequate or improper roof maintenance

Roof leaks caused by use of defective roofing product

Roof leaks that aren't - indoor moisture, stains, water, leaks mistaken for roof leaks.

Tracking Down Roof Leaks to Their Source

Following roof leaks to their source

How to Decide if a Roof Leak is Active or Old, How to Handle Wet Moldy Areas Discovered in a Ceiling

Question: How do I track down roof leaks and decide if leaks are active or inactive? Wet spots & black mold found during interior repairs after prior roof leaks and a new roof installation

Reply: Look for & trace moisture or water under the roof, explore for leaks during mold cleanup, don't look just for "black mold"

Follow the water pattern and moisture levels to track down flat roof leaks

Roofing over wet materials can lead to further trouble

Mold Under Leaky Roofs - some basic advice

Leaky masonry walls remain on your project - watch out for rain and storm damage such as from Hurricane Irene

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Roof Leaks: diagnosis & repair guide
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