Evidence of deep building flooding (C) Daniel Friedman Water Entry & Water Damage to Buildings

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How to diagnose the cause of & how to cure building leaks & water entry: key concepts for an effective approach to building, basement, or foundation leaks & waterproofing, how to dry out a wet or flooded building, how to determine a building's leak history, and the age of leaks & water damage.

This series of articles explains the causes of building water entry, leaks, or actual flooding of buildings and describes how to fix building water entry problems.

We describe the damage that is caused by flooding, water entry, or smaller leaks, and we explain how best to cure water entry problems in buildings using a series of measures to keep water out of the building basement or crawl space (or other areas), how to get rid of water or wet conditions in a building, and how to correct building damage, mold, rot, etc. caused by water entry.

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Building Leaks, Water Entry, Flooding, Moisture: Diagnosis, Evaluation, Cure, Prevention - Key Concepts

Photograph of moldy pantry shelf.We include a series of detailed "how to" articles for stopping and fixing building water damage.

Our page top photo shows our client pointing to flood lines on a heating system expansion tank, indicating that this building was subject to severe deep flooding. We learned from neighbors that a nearby river had flooded this home and others in its neighborhood repeatedly over the 60 year life of the building.

If your building has been flooded by hurricane, tropical storm, burst pipe, or other water problems, see FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP.

Also see BASEMENT LEAKS, INSPECT FOR where we describe procedures for finding evidence of the frequency, extent, source, and causes of leaks, water entry, and actual building flooding - a critical step in evaluating a building as well as in planning the cure for building leaks, water entry, and mold.

Article Contents

The most basic advice we can give on stopping or preventing basement or crawl space water entry is that it's best to find where and why water is leaking into the structure and to correct that source - usually it's outside the home.

If there are reasons that you really cannot address the water problem at its source, a second best approach is to choose among various methods for keeping water out of the building at the last minute - from inside, combined with steps to dry out or remove excess indoor moisture or water, combined with avoiding generating excessive moisture by proper handling of moisture coming from indoor activities.

Here we begin a article series on drying out a wet basement or crawl space and keeping it dry.

Wet basement signs (C) Carson Dunlop Associates

Visual inspection of a the exterior and interior of a building can provide ample evidence of the history of leaks and water entry at a property.

Carson Dunlop Associates' sketch (left) shows some clues that easily indicate a history of wet basement troubles.

Even when a building is brand new, an experienced home inspector or waterproofing or de-watering contractor can spot conditions that are likely to lead to future leaks, water entry, flooding, and moisture or even mold problems at a structure.

At BASEMENT LEAKS, INSPECT FOR we describe how to inspect a building for evidence of its history of leaks, water entry, or flooding.

How Long Does It Take for a Building To Dry Out After a Flood or Leak

Our photos below show the basement dry-out procedure for a New York home that had water entry from a foundation wall leak. Because a finished floor had been put down over wood sleepers, it would have been virtually impossible to dry out this space without pulling up the flooring.

The contractor also removed the bottom foot of all drywall to permit inspection of wall cavities for leak signs. It was that step that allowed us to trace this basement soaking to a single foundation wall crack.

Wet basement dryout procedure (C) Daniel Friedman Wet basement dryout procedure (C) Daniel Friedman

The length of time required for wet conditions in a building to dry out is quite variable, depending on multiple factors. The time for water to dry in a wall cavity can be substantial, depending on:

  • the original wetness level: Was the building flooded, was there a plumbing leak, is the moisture due to trapped condensation?
  • the building materials involved: more porous materials dry more rapidly and permit the cavities they cover to dry more rapidly
  • the amount of air movement in and out of wet or damp building cavities as well as along the outer surfaces of damp materials or wet building cavities (this is why we supplement use of dehumidifiers with area fans when drying out a building).
  • the permeability of building surface coverings: more porous materials dry more rapidly; building walls, floors, ceilings that include openings or cracks might dry more rapidly, but probably unevenly and unreliably nonetheless
  • temperatures and relative humidity outside the wet building cavities on all sides
  • other factors such as weather involving wind (and wind direction), intermittent rain or snow, etc.

A Comparison of the Effectiveness of Basic Building Dry-Out Procedures

Wet basement cures (C) Carson Dunlop AssociatesWe have inspected numerous buildings after flooding or severe plumbing leaks, and we have examined and tested the results of various building dry-out, "de watering", or "water extraction" methods used by contractors.

Carson Dunlop Associates' sketch (left) shows common measures to control roof and surface runoff to get water away from the building. In general this is the first step in stopping or preventing wet basements or crawl spaces.

Detailed Investigation to Determine the Extent of Basement Water Entry

Even when drywall is measured (using a moisture meter) as "dry", we have pulled off wall baseboard trim to find visible water and soaking conditions in such locations.

Readers who need to know how to properly respond to flooded buildings should see our series of articles beginning


  • Simply operating a dehumidifier and/or fans will not remove moisture from wet building cavities fast enough to avoid a risk of hidden mold contamination.
  • Making small 2" diameter openings along the bottom of a wall, or even along the bottom and top of a wall between each wall stud pair in order to try to speed wall cavity dryout has proven ineffective and has resulted in severe mold contamination in some locations.
  • Strip cuts at the entire length of the bottom of walls in a room that has been flooded, removing the bottom 12" of drywall or plasterboard is often sufficient to dry out cavities that were not flooded to higher levels, but check for wet materials such as wet insulation at higher levels in the wall cavity and extend the strip cut higher as necessary.
  • Complete wall covering demolition indoors is often needed on at least one side of the wall to rapidly dry cavities that were wet from above, such as during a fire extinguishment, an upper floor plumbing leak, or severe building flooding. Similar approaches may be used for wet ceilings.
  • Wet carpeting needs to be removed and disposed-of;
  • Wet finish flooring that has buckled or moved will probably have to be demolished. Often it is possible to allow subflooring to remain in place if it is not water-damaged.
  • Wet building insulation needs to be removed and disposed-of, not re-used.

Six Topics to Sort Out Building Leaks, Water Entry Cause, Cure, and Prevention

A series of detailed articles addressing these categories are listed below. Contact Us to suggest changes and additions to this material.

  • Present building condition: how wet or dry is the building, what building surfaces or cavities have become wet, what steps have already been taken or need to be taken to dry out the building.
    See WATER ENTRY in BUILDINGS for a discussion of sources of building leaks, moisture, and moisture related problems other than actual building flooding.
  • Building water entry damage control: what emergency steps should we take to minimize damage to a building that has suddenly been wet by leaks or flooding? (If your home has been flooded
    see FLOODS IN BUILDINGS-priorities first)
  • Building water entry history: Identify evidence of the leak, water entry, moisture, or flood history at the building.
  • Building water entry causes: identify building or site conditions likely to cause leaks, moisture, basement or crawl space water entry, or actual flooding at the building. Often on older buildings there has been a history of water entry and there may be multiple sources of water entry, confusing insurance claims as well as proper building repair procedures.
  • Building Leaks & water entry cures: what should we do, in what priority order, to stop recurrent water and moisture problems at a building?
  • Building water entry and flood damage prevention: what should we do at any building to prevent future leaks, condensation, water entry, or actual flooding at a building

Evidence of Prior Building Water Entry & Flooding

Flood lines in a crawl area (C) Daniel Friedman

This home inspection client was not happy to learn that the home she had recently purchased had been the subject of recurrent basement and crawl space flooding.

Flood lines in a building indicate the depth of water entry. Careful observation of water and mud stains can also indicate the number of significant floods that have occurred as well as possibly their frequency.

Even after a post-flood cleanup it is usually the case that clues of a building's history of leaks and water entry can be found.


Also see FLOOD Damage Assessment & Repairs.

How to Sort Out Evidence of the Age & History of Water Entry or Leaks In a Building

Photograph of moldy pantry shelf.Here is an approach to get a better idea of the building leak and mold or other water damage history.

Three types of wet-building events

Often one can easily spot the difference between

  1. a single water entry or leak event that wet a building - no other wet building areas, no other clues indicating prior leaks
  2. chronic water entry or wetting events - recurrent wetting of the same area from the same cause (or rarely, from different causes), often seasonal or weather related, such as during spring thaw, spring flooding, or hurricane season
  3. episodic but not chronic wetting events (a roof leak 10 years ago that soaked attic and wall cavities, a fire 10 years ago that soaked entire building floors, a burst pipe last week) - by noting water leak evidence in varying, disparate, even not-connected, or not entirely overlapping wet areas and events; correlate leak events to known hurricanes, floods, storms

In our photo above, our screwdriver has pushed easily in to its handle through the bottom of a wood post set into a concrete floor. Look closely and you can see water lines about five inches up from the floor on this post bottom and much lower water stains on the bottom of the stair stringer in the upper right of the photo. Give careful thought to the conclusions you'd draw from this example.

Even without basement flooding a wood post set through a concrete floor slab is likely to suffer rot or insect damage at its hidden end.

See BASEMENT LEAKS, INSPECT FOR for more clues indicating the history of water into a building's lowest floor.

Distinguish Among Recent Water Entry or Flooding & Old or Chronic Water Entry & Flooding in a Building

Mold behind paneling (C) Daniel Friedman

  1. A recent water entry/flood event or an old, single-water-entry event: look for wet areas, stains, mold, but with no long term deterioration of materials (rot) due to water. Note that mold contamination can occur in 24-48 hours after a flooding or water entry event, depending on local conditions; cool temperatures slow the onset of mold contamination, and of course mold growth depends also on just what materials were wet. More about mold and chronic water entry is just below.
  2. Recurrent or chronic water leak area: look for wet or dry but stained areas, suggested by
  • evidence of rotted or decayed wood trim - check the back side of floor baseboard molding, unlike mold growth, rot doesn't show up in just a few days after a flooding event
  • check height of water stains behind vertical door trim moldings 
  • check for multiple stain lines that may indicate multiple water entry events, though watch out as slowly receding floodwaters can also leave multiple stains on vertical surfaces

Our photo at above left shows me finding significant mold contamination behind paneling that itself looked perfectly clean; the floor trim in this basement was also intact and it was difficult to find clues suggesting prior flooding and certainly there was no evidence of chronic water entry.

But the owner's daughter had immediate breathing difficulties and asthma attacks immediately on entering this basement area - in fact her reaction started when she opened the door to the basement. On reviewing the history of the home the owners noted that more than a decade before there had been a burst sewer line and sewage backup that wet the basement floors. All exposed surfaces were cleaned, dried, disinfected within 24 hours. But no one thought about the wetting that had occurred within the wall cavities and behind the paneling.

Study Trim & Trim Hidden Sides to Learn Building Leak History

Our photo at below left shows door and floor trim removed from a home that had experienced a single-event flood from a burst toilet tank. Notice that although these trim components had been wet, there are no stains, no rot, no mold evident in the picture. This suggests that these components had not been subjected to recurrent flooding or wet floors.

Floor trim exploration for water leak signs (C) Daniel Friedman Photo of water stains and mold behind vinyl floor baseboard trim (C) Daniel Friedman

At below left, we have removed (without damaging it) floor baseboard trim to show the absence of any water stains on both the hidden side of the trim as well as on the drywall behind it. This area has not been wet since these materials were put in place.

At below right, we have two clues of prior water entry: the stains and fungal growth on the back side of the plastic baseboard molding trim and on the wall surface behind it; and while plastic baseboard trim is widely used (e.g. in kitchens and baths and some commercial areas), in a finished residential basement above a tile or concrete floor, its use may indicate that previously people got sick of dealing with wet floor problems there.

Floor trim exploration for water leak signs (C) Daniel Friedman Photo of water stains and mold behind vinyl floor baseboard trim (C) Daniel Friedman

Watch out: mold growth in a building may be quite recent (just a few days old) to months or even years. Some mold growth details and growth structures can suggest that there has been a long-standing mold contamination problem in a building.

See AGE of MOLD, HOW OLD for details.

At below left, the thick mold on the underside of the pantry shelf occurred following a single event building flood in a home that was left unattended for weeks or longer. But if you find rot on wood structural members, floor sills, or on the back side of floor baseboard trim (Photo below right), then this component and this building area has been wet repeatedly and over a long time.

Photograph of moldy pantry shelf. Photograph of moldy pantry shelf.

How to Study Carpeting Tack Strips to Learn the Building's Wet Floor History

Here we illustrate how to sort out among four wet floor cases:

  1. clearly the floor and carpet were never wet
  2. the floor and carpeting have been wet at least once, probably not repeatedly
  3. the floor and carpeting have been wet at least once, and we are not sure if it was chronic or not - (let's be honest here)
  4. the floor and carpeting have been wet certainly more than once, chronically

Our photo at below left illustrates carpet tack strips that have in our OPINION never been wet more. Notice also there are no water stains on the OSB subfloor around the tack strip, BUT the surface itself looked a bit rough - a condition that can be caused by water. That rough surface of the OSB made us decide we needed to look further under this carpet. What we found is shown in our second photo, below right. There was evidence of what appeared to be a single-event flood.

Notice the water stains on the tack strips in the upper photo areas as well as water stains on the subflooring. This sequence illustrates the danger of too-hasty spot-checks for water entry. In the photo at below right, in that picture's lower left corner you can see that the owner had installed new carpet tack strips in some areas when a previously-wet carpet was replaced. That's what our first photo at below left had discovered.

How to study carpet tack strips for history of building water entry (C) Daniel Friedman Photograph of moldy pantry shelf.

Let's not pretend we can be more certain about building water entry history than is appropriate to the evidence at hand. At below left, to me the carpet tack strip looks like one that remained wet for some time - the nails are quite rusty and black stains have spread into the wood of the tack strip.

But I don't see rot nor significant damage at the wall itself. This could have been a single event wet floor that stayed wet for longer than just a few days; or there may have been more than one wet floor event. I'm uncertain.

In contrast, our photo at below right illustrates carpet tack strips that have in our OPINION almost certainly been wet more than once. Also note the rust stains on the bottom of the carpet itself.

How to study carpet tack strips for history of building water entry (C) Daniel Friedman Photograph of moldy pantry shelf.

But here is a water entry case that we can sort out. At below left I've pulled back carpet in a corner (that's the easiest place to pull up wall-to-wall floor carpeting without tearing it) to show dark stains and damage to the tack strips and some stains on the back of the carpeting itself.

To me this looked like chronic water damage. Now taking a close look at the bottom of the baseboard trim at the floor-wall juncture (photo below right), you can see unequivocal evidence of chronic water entry: the bottom of the floor trim is rotted. This was not a single-event wet floor.

How to study carpet tack strips for history of building water entry (C) Daniel Friedman Photograph of moldy pantry shelf.

Links to Key Articles on Diagnosing & Curing Moisture and Water Problems in Buildings

Clogged footing drain (C) Daniel Friedman

Photo of a mud-clogged footing drain

Our client saved this partly-clogged footing drain that was excavated from around their nearly-new but very wet home to show how quickly soils can enter and block drainage at a property if the system was not properly installed.

Scroll down to see our links to building water-entry related articles on the detection, diagnosis, cure, and prevention of building water damage and water related problems such as rot and mold.



Comment on Using Moisture Meters During a Home Inspection to Screen Buildings for Leaks or Mold

Delmhorst pin type moisture meter with long probes (C) Daniel FriedmanQuestion: will my inspector test for moisture?

I am scheduling a pre-purchase home inspection and my real estate agent asked a question about moisture detection: he wants to know if the home inspector will check the moisture level in Sheetrock? - C.W., New York, NY.

Reply: ... it depends ...

Moisture meters, particularly pin-type probing moisture meters that detect moisture by sending an electrical signal between two probes inserted into a material (such as the time-tested Delmhorst™ twin-point electronic resistance moisture meter shown at left) are one of the first tools that many building inspectors purchase after a flashlight, ladder, and screwdriver.

Relying on any test instrument, as we discuss at GAS DETECTOR WARNINGS , is not a good substitute for a careful inspection. While using a moisture meter is a popular tool among home inspectors and building environmental inspectors or "mold investigators", and a useful one, the visual inspection of a building for leak history is much more critical than a general "check" using a moisture meter.

Tramex moisture encounter in field use (C) Daniel FriedmanAfter all, the building could have had a history of leaks in the past, as well as hidden rot, insect damage, or mold, related to leaks or trapped moisture, but the leak spot could happen to be dry at the time of testing.

Absence of evidence of moisture when using a moisture meter in a building is not evidence of absence of a history of building leaks, and there is a long list of visual clues that readily tell the story of a building's leak history or the risk of building flooding. .

So properly a moisture meter is, in our opinion, useful principally to confirm that a leak is current. We also find moisture meters useful, particularly radio-signal based non-probing moisture meters such the Tramex™ electronic moisture encounter, to check for hidden leaks behind ceramic tile walls in bathrooms and kitchens where probing is impossible.

Tramex also makes pin-type moisture meters.

And certainly "spot checks for moisture" done randomly at a building would be nonsense.

In a field study we conducted in February 2004 we compared the effectiveness of various methods to test for moisture in the walls of a home reported to have suffered leaks from ice dams at its roof eaves. We surveyed the inside surface of building exterior walls of the entire second floor front and rear building surfaces using the popular tools and methods - the results are reported at MOISTURE METER STUDY.

Home buyers and home owners are right to worry about building leaks and moisture - water where we don't want it is at the top of the list of sources of building problems. If you have a particular reason to be suspicious about something be sure to let the inspector know.

Watch out for "show and tell" tools that impress the client but are a poor substitute for doing a good job.


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