Roof Leaks: diagnosis & repair guide
A complete catalog of sources of leaks in all types of roofs & help tracking a roof leak back to its point of origin
ROOF LEAK DIAGNOSIS & REPAIR - CONTENTS: 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
POST a QUESTION or READ FAQs about how to diagnose & repair leaky roofs: finding the point of leakage, fixing the roof leak, preventing future roof leaks
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Roof leak diagnosis & repair:
This article series provides an extensive catalog of sources of leaks in all types of building 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.
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.
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 the "More Reading" links at the bottom of this article 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".
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:
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 top or at the "More Reading" links at the bottom of this article .
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
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:
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
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
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.
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.
ROOF ICE DAM LEAKS - 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.
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.
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