Wet or damp basement cause, diagnosis, cure & prevention: this article describes visual inspection methods and clues to detect basement leaks, water entry, flooding, or just high moisture problems.
Finding where basement or crawl space water is coming from is the first step in fixing foundation leaks and wet basements. Here we illustrate common basement water entry leak points and signs that can be seen from inside the building.
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Wet Basement Diagnosis: a Guide to Inspecting for Basement Moisture, Leaks, Flood History, or Chronic Water Entry
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Image at left provided courtesy of Carson Dunlop Associates.
A clear answer to where basement leaks originate avoids falling prey to the rising ground-water or there's a stream under the house fib that sometimes leads homeowners to installing an expensive fix for the wrong problem.
Where to Start Diagnosing Building Water Entry & Wet Basements - Outdoors
In this article we begin with a catalog of basement or crawl space water entry signs seen from inside the structure. Our opinion is that an expert inspection for a building basement or crawl space water entry problem begins outdoors with an inspection of the site, roof drainage, and similar features
But there are plenty of indoor clues of water leakage problems in buildings, and they can be found on every level of the structure.
Is Your Indoor Moisture or Water Problem Rising Damp, or do you have Basement or Crawl Space Water Entry Leaks?
This article explains procedures for inspecting in the building basement for signs of leaks and for sources of building moisture that could even be appearing as attic condensation or building mold.
Rising damp, according to the Building Doctor Joseph Knight, a Chartered Surveyor in the U.K. (a place where they know about dampness), describes rising damp as
... upward movement of moisture through the pores in masonry, caused by ... capillary action which relies on the surface tension of moisture to draw moisture vertically [upwards into the building foundation and masonry walls] from the ground.
Think water molecules moving upwards through building materials, not puddles on the floor.
Building water leakage, in our view [DF] refers leakage of liquid water into a structure from any source: roof leaks, roof spillage on the ground that passes through the foundation wall (our photo at left), surface runoff or groundwater that leaks into a building through its lowest level floor or lower foundation walls.
The distinction between rising damp and water leaks is is important because a proper diagnosis of the cause of high moisture or actual wet conditions assures that we fix the right problem. If water is leaking into the basement from roof spillage on the ground outside, the best fix starts with the roof gutter and downspout system, not with installing an interior perimeter drain or foundation waterproofing to "fix rising damp" as may be sold by some contractors who are more in a rush to do the job than to diagnose the problem.
The photograph at page top shows a very wet basement with water stains high on the foundation walls - telling us that the cause of this water entry is obviously not "rising damp" nor "construction over an underground stream".
The photo at left shows the author (DF) as a much younger and better dressed building inspector than today, pointing out that water stains on the foundation wall were originating at the very top of the foundation . Pointing out the location and height of water stains and wet marks on a foundation wall is a useful diagnostic step in figuring out where basement water is coming from.
While rising damp can indeed produce moisture and efflorescence on building walls and floors
These basement water entry inspection recommendations are based on 35 years of building inspections, on the observation of the locations of moisture, mold, ice dams, condensation stains, efflorescence & white or brown deposits, water stains, and other clues in buildings, and on the correlation of these clues with the roof venting conditions at those properties as well as frequent literature review and discussion among professionals.
Carson Dunlop Associates' sketch (left) shows some clues that easily indicate a history of wet basement troubles.
Readers should see WATER ENTRY in BUILDINGS and
also see WET BASEMENT PREVENTION where we describe the basics of preventing basement or crawl space water entry, report a foundation collapse case study, and describe some simple steps that may cure a wet basement without major expense.
Basement trim water stains can be a good indicator of a history of wet basement floors. In our photos below we illustrate a cute attempt by someone to "hide" the water stains on basement door trim by placing little stuffed animals in the doorway. First the skunk, then the little squirrel happened to tip over, disclosing that the little rascals had been hiding water stains.
Moisture from a wet building basement or crawl space travels up through the building where it can often condense in an attic, causing mold, frost, and even rot in a building if proper under-roof ventilation is missing.
In the case of the basement shown at page top, we also need to correct the cause of basement water entry - in this case almost certainly it's a roof spillage or gutter problem since we see water stains so high on the foundation walls.
In the basement shown at left there has been flooding, a mold problem, and perhaps other moisture damage in the building.
But further investigation, both outside and indoors, will be needed to fully explain why water is on the basement floor.
3 Levels of Basement "Wetness" - Inspecting in the Basement for Sources of Building Leaks or Moisture Appearing as Attic Condensation
Because building leaks, water entry, and flooding and their related damage, ranging from structural damage to costly mold damage are such a large topic, we divide our building water problem inspection, discussion, and advice into these major categories:
Three Degrees of Building Wetness
We divide our wet building thinking into these degrees of severity: Damp, Wet, and Flooding. Here are our definitions of each of these levels of building water entry:
1. Damp or moist conditions in a building: in most areas basements and crawl spaces are damp; certainly anywhere that we have masonry construction below ground level we can expect higher humidity and dampness; depending on the degree of moisture and other building conditions, damp or moist conditions can cause mold or other building problems.
As our photo shows, water seeps up through cracks in this Staatsburg NY basement floor. Staatsburg is built on a wet swampy flat area in Dutchess County. If your basement is dry, you probably don't live in Staatsburg.
3. Flood conditions in a building: water extends over the entire building floor, extending from a fraction of an inch to virtually filling the building and even flooding upper floor levels if a building is located in a flood plain or flooded area.
At below left our client points out that basement flooding had reached at least this far up from the basement floor - leaving mud on the bottom of an expansion tank. In this neighborhood we also found flood-deposited mud atop sill plates at foundation wall tops.
Our second photo, at above right, is really an outdoor clue, though you might see this from the inside: it's a foundation flood vent, indicating that the builder thinks the building is in a flood prone area.
Another important observation about the causes of and cures for attic moisture condensation is that buildings with an attic moisture condensation problem very often have wet basement or crawl space water entry problems.
In fact even before entering an attic to inspect for moisture, while still outside
I often look at excessively curled asphalt shingle roofs and suspect a basement water entry problem.
The presence of moisture staining high on the wall confirm that the water source is either roof runoff spillage against the foundation or a surface water runoff problem.
This is not a case of "rising groundwater" or "a buried stream".
A careful study of the pattern and location
of moisture stains gives important diagnostic information about the probable source of basement water entry
and of leaks or building moisture problems in general.
Carson Dunlop Associates' sketches (left and below) show some additional clues that easily indicate a history of wet basement troubles as well as how people may be dealing with recurrent basement flooding by an interior perimeter drain, exterior drainage, or sump pumps.
Watch out: basement leaks and high moisture travel throughout the building
Actual basement flooding or simply high basement moisture forms a moisture source in a building that affects the entire structure.
An attic inspection that discovers attic condensation should direct you to go back to inspect the basement for leaks.
Our photos show part of a collection of basement sump pumps found in a single location - a strong indicator of a history of basement water entry trouble.
Moist air rises through the building by natural convection, eventually
finding its way into the attic or roof cavity. If the roof cavity is not adequately vented, moisture
will condense there leading to building damage and perhaps an attic mold problem.
In fact even correcting the inadequate attic venting (as we describe below), will be insufficient if a basement or crawl space source of attic moisture was also present and if it remains un remediated.
Carson Dunlop Associates' sketch (left) shows additional clues that easily indicate a history of wet basement: rot at floor joist ends and sill plates atop the foundation wall.
On occasion we find mud in this location, indicating perhaps that the home was previously flooded.
This photo (above) shows strong evidence of a history of water entry through the foundation wall at right: stains on the bottom stair riser appear to emanate right out of the foundation wall.
And that projection of concrete poured along the wall bottom is often a sign of an attempt to retrofit a water seal at a point of water seepage at the wall/floor juncture. If that guess is correct, that might explain why the stair riser is water stained - the concrete "seal" couldn't extend between the stairs and wall without demolishing and rebuilding the stairs themselves, so behind the first stair tread a leak point remained un-sealed.
A look behind this stair [photo] confirmed just what we thought.
Carson Dunlop Associates' sketch (left) shows places to look for rust as an indicator of basement leaks or high moisture levels:
Rust stains at drywall nails or screws
Rusted or stained carpet tack strips
Heavy rust especially at the base of steel Lally columns or on steel beams (see our photo, below).
Rusted metal screws, nails, and structural connectors connected to the foundation wall
Rusted feet on a basement-located oil tank
Rust or water stains on the bottom of heating equipment that rests on or close to floor level, or if you see that heating equipment has been installed on concrete blocks to lift it above floor level that may also indicate a concern for a history of leaks and water entry.
An example of Carson Dunlop's tip to look for rust or water stains on metal beams is shown in our photograph (below left). This steel girder was supporting a modular home that had been driven in rain and received extensive highway-blown water inside the structure.
Our second structural rust photo (above right) was very exciting. We were inspecting a house on Long Island when the owner mentioned that she had pumps running 24/7 in the basement to keep the bay at bay. All of the Lally columns (some were just hollow pipes not real Lallys) were badly rusted.
Details are at COLUMNS & POSTS, DEFECTS.
Also see FLOOD DAMAGE TO FOUNDATIONS.
For problems with settlement of piers below Lally columns see SETTLEMENT CRACKS in SLABS.
Our photos below are clear examples of a severe basement flood. If you inspect closely you may find multiple apparent high-water lines on basement surfaces or contents. Don't assume this is necessarily multiple flooding events. The lines may be multiple separate events, or they may be stages in lowering of the water level in a flooded basement. Additional clues (such as rotted floor trim) can distinguish between a one-time basement flood and recurrent water entry.
Our second photo shows our inspection client taking a break next to flood lines on a warm air furnace base.
More basement water entry clues: details on walls
Carson Dunlop Associates' sketch (left) shows additional clues that may point out a history of wet basements:
Concrete block or poured concrete foundation wall spalling
Patches in finished drywall
Deterioration of drywall at or close to floor level
Stains or rotted floor baseboard trim
Where plaster is applied directly to the foundation walls look for soft spots or efflorescence.
Concrete Foundation Wall Leak Points - Leaks at Cold Pour Joints
At COLD POUR JOINTS, CONCRETE we discuss the cause and possible significance of cold pour joints on a poured concrete foundation wall.
Usually a cold pour joint in a concrete wall is only of cosmetic import. But if sufficient time elapsed between successive concrete pours into an individual foundation wall, the lower wall concrete "sets up" enough that there is a poor bond between that layer and the next pour of concrete into the wall forms.
The result can be not only a visible "crack" in the poured concrete wall, but this cold pour joint may leak surface water or ground water into the building. Our photo (above left) shows white efflorescence stains left by a long history of building foundation leaks at a cold pour joint on this building.
Also notice that in the corner there was some efflorescence above the cold pour joint, while at the second photo (above right) there was efflorescence and leakage only below the cold pour joint. At both of these locations a roof drainage downspout had spilled water against the building wall for many years.
In our two photos above, the two areas of leakage, at the cold pour joint in the building corner, and further along to the right of that corner in a lower cold pour joint leak, you can see that water leakage was concentrated (shown by the white efflorescence on the wall).
Our photo at left shows a closeup of white mineral salts (efflorescence is discussed at Efflorescence & white or brown deposits) left on the concrete foundation wall below a leaky cold pour joint.
So routing downspouts well away from the building and terminating the downspout at a location where water will continue to run away from the building rather than back towards it would probably have prevented most or all of this basement water entry problem as well as the mold contamination that it led to.
Form ties are usually steel wires or rods that secure the front and back foundation wall forms in place during a concrete foundation wall pour. After the wall has cured the ties are cut or broken off.
On (usually rare) occasions we find water leaks through the poured foundation wall at the form ties, as shown by the stains in this photo.
The significant volume of leakage along this basement wall suggests that there was an outdoor problem with surface runoff or mishandling of roof runoff around the building.
Episodic water leaks through this crack sent water into the wall cavity and below a raised floor in the basement where it was un-noticed until a severe rainfall and leak quantity brought enough water into the basement for water to appear above the finished floor level.
The exact location of the leak was apparent once we removed the basement wall and floor coverings - a step that was necessitated by a mold-contamination problem that originated in basement water leakage.
Our photo (below left) shows a normal concrete floor slab shrinkage gap where the floor (under our pen) abuts a poured concrete foundation wall.
The brown material on the floor is mud which we suspect rose up from below the slab when surface runoff or ground water saturated the soils around and under the floor slab.
Our second photo, above right, shows minor seepage through the concrete foundation wall at cold pour joints. Most cold pour joints are not leaky, but this one was.
There are two common explanations for the water seepage pattern shown here:
1. The footing drain is absent or clogged - notice that the wall at right looks pretty dry except along that first course of block. This might suggest that water is not running down this foundation wall from above.
2. Sometimes a serious water source along one foundation wall will enter the block walls and travel around to other sides of the foundation through the hollow cores of the masonry blocks.
This circumnavigation of the foundation wall interior through the hollow core concrete blocks is particularly mobile if the basement floor slab is poured half-way up the first course of block, forming a dam that raises water level inside the wall and encouraging water travel in the wall interior.
Our photo (left) shows water stains down a poured concrete foundation below an EIFS-clad new home.
Leaks at window sills and other exterior EIFS wall penetrations allowed wind-blown rain (or spray from a garden hose) to soak the wall cavity, wall insulation, and to appear as streams down the foundation wall beginning at a height several feet above ground level - compelling evidence that this is not a roof spillage nor ground water leak. It's an exterior wall leak showing up in the basement.
We had a wonderful Gary Larson cartoon here, showing a wet basement, but at Mr. Larson's request removed it. - Ed. You'll just have to think "Gary Larson" an d "Flooded basement" and come up with a funny image.
Water-damaged, curling, lifting floor tiles are a likely indicator of a basement flood or recurrent wet basement floors. In this basement, all of the floor tiles had come loose, but the rectangular marks show where they had previously been located.
The use of plastic floor baseboard trim (plastic cove molding) in an older home may indicate that water-damaged wood trim or even water-damaged lower portion of drywall close to the floor have been covered with this wider, water-resistant material.
High moisture, even without actual flooding, can cause wood flooring and some laminate floors to buckle.
This laminate engineered wood floor was badly buckled and eventually just popped up after water had leaked under the floor installation.
Continue reading at WET BASEMENT PREVENTION or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: how to diagnose the cause of ceramic tile failure over a wet floor or crawl area
I have just been looking at your article on wet basements and noticed the photo you have curling, lifting floor tiles . I have just experienced the same problem whereby about 50% of my ceramic tiles slowly started to have a hollow sound when knocked. I removed them and found all the tile glue attached to the bottom of the tile, and the same pattern was left behind on the concrete floor of where the tiles have been.
The tiles were laid 2 years ago. Also when lifted the tiles were moist and the gout lines left on the floor seemed to be softer than the rest of the concrete. There originally was a raised wood floor in my apartment when I moved in, but two years ago it started to rot and buckle.
My insurance company took a look and found that a un-insulated hot water pipe feeding water to the apartments above was running under the floor and was the most probable cause, pulling ground water up and turning it into steam ? The pipe was replaced and insulated, and I was told that the best thing for me to have on my floor was tiles, and floor heating.
So I had a plumber install a hot water floor heating, and had about 2-3 cm of self leveling concrete poured over it. The guy who poured the self leveling concrete told me that it will be ok to lay tiles in 7 days or so, which I did and turned on the floor heating several days later.
The thing is, many people are telling me the problem is I didn't wait long enough for the self leveling concrete to dry properly, and if I clean and re prime the floor it will be good. But I am worried that the floor heating is creating the moisture and the same problem will happen again. Can you please give me some good advice. It has been suggested that I turn off the floor heating and replace just one tile and if after a few days it remains firm it will be safe to proceed to lay the others ? But I am very wary, and cannot be sure what to do ? I hope you will reply with some good advice.
A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone. You will find additional depth and detail in articles at our website. That said I offer these comments:
Frankly I think your insurance company was barking up the wrong tree. An uninsulated hot water pipe won't place water in a floor structure (unless the pipe is actually leaking), in fact it would have the opposite effect: it's heat would cause things to be more dry than ever. Really I am a bit embarrassed to have such a strong reaction to a question but I can't make any sense out of the diagnosis you received. It sounds like wild arm-waving. Or somehow I have completely misunderstood your question.
For a hot water pipe to cause other ambient moisture to flash to steam we'd have to be heating the water to over boiling - over 212F; A domestic hot water pipe should be running no more than at 120F to avoid scalding and comply with building codes in most areas.
You have a water source (I don't rule out ground water if the floor was not properly built), or pehaps an actual leak somewhere. An uninsulated COLD water pipe could drop condensate into a floor structure but enough to cause rot in just two years sounds unusual to me. I'd look for some other leak into the floor.
About curling floor tiles - that occurs with vinyl type floor tiles installed where the floor has been wet from leaks from any source; ceramic tiles don't curl; But they might indeed come loose if the floor and subfloor are wet;
More information about how the floor was constructed, and the crawl area conditions below the floor, are essential to make sense out of this question; meanwhile I suggest that you do not do anything costly by way of "repairs" before we are confident that we understand what the heck is going on.
Thank you ever so much for your speedy response, I am including 2 photos of what the floor looks like after I removed the loose tiles. I think the issue is definitely ground water,as the house was built in 1929, and although the sewage pipes have all been renewed, the rain water drain pipes that go around the exterior of the building are the original concrete ones. I have been told that they should be dug out and new plastic ones put in deeper down that are perforated in a way that will collect the ground water and prevent it going under the house. But as it stands at the moment the other 5 apartments that are above mine are reluctant to get them repaired because of the cost.
I had a building inspector round and he told me paint the floor in the adjoining bedroom where the damp readings in the floor are highest with a damp proof material before I lay the tiles . As for the living room floor where the tiles have come loose,the damp readings are quite OK ( but I am wondering if it is not because I have heating in the floor?)
The inspector has told me to use a better tile cement than I used previously and just replace them.( I think I would be more comfortable painting this waterproof primer on before,but it is about 2mm thick, so there will be a discrepancy in height with the rest of the tiles that are still strong on the floor.)
As I said before, when I removed the loose tiles all the cement was stuck to the bottom of the tiles with little or none on the floor.(Although the tiles that remain down seem to be strong enough?) Also they were slightly damp when lifted.
Several people believe the reason could be that I put them down without allowing sufficient time for the self leveling concrete to dry (it was about 2-4cm thick, and I laid the tiles after aprox 7/8 days almost 2 years ago) ,and that the residue water from the concrete got trapped under the tiles unable to evaporate?
Or that I turned the floor heating too soon, or too high too soon? A tile specialist has recommended that I just put one tile back to start with, then try and get it free in a few days after it has set. He said if I need a hammer to break it loose it will be safe to put the others back. I will be looking forward to your reply Daniel, meanwhile I have the tedious task of scrapping back the glue from the lifted tiles .
Originally you said "There originally was a raised wood floor in my apartment when I moved in, but two years ago it started to rot and buckle" but It's not quite clear to me how your home was constructed and whether we are talking about a wet damaged tile floor over a basement, crawl space, inaccessible crawl area, or slab on grade. That detail would help determine how best to inspect the water damage problem.
Regarding the rain water drain pipes that go around the exterior of the building are the original concrete ones. I have been told that they should be dug out and new plastic ones put in deeper down that are perforated in a way that will collect the ground water and prevent it going under the house.
While clearly someone corresponding by email can't be as properly informed as an onsite expert, this advice does not sound correct to me. First, if the roof drainage system is properly sloped it does not need to be deeper nor below the frost line.
Second, we never want to tie the roof drainage system into the (much deeper) foundation or footing drain system - it sounds as if your advisor may have been confusing those two systems. Doing so overloads the footing drain and invites water entry through the foundation near its bottom;
Third, we do not want to put perforated roof drainage system pipes close to the house to carry off roof drainage. Doing so invites foundation leaks. Rather that water needs to be delivered to daylight well away from the building where it won't return, or delivered to a storm drain system if local codes permit that approach.
Fourth; an old, "original" roof runoff handling piping system is very likely to have clogged or failed by now; if those original drains come to daylight it's easy to see if the drains seem to be working; if the drains do not come to daylight nor to a storm drain, then they are not working.
About the leveling compound dry time: I don't know the if tiling over wet cement was the original problem: tiles would have come loose early after installation, and more, opening the floor years later would not show wet conditions; if you found wet conditions two years after an original tile job, there was a current water or condensation source.
About priming the floor as a "fix" for a prior tile job failure, that advice sounds a bit inadequate as a solution to a floor built over a wet area or a damp surface; you would be relying simply on a thin coating of primer to keep water out of the floor structure, after already allowing it into the subfloor where over time you risk rot, insect damage, and floor disassembly.
The proper approach is to find and fix the source of water entry. While on occasion there is indeed a ground-water problem at a property, experienced home inspectors and honest basement waterproofing contractors will tell you that 90% of the time or more the problem is not "rising damp" and not "ground water" but rather mis-handling or inadequate handling of roof runoff or surface runoff around a building.
In sum, my view is that it would be a mistake to repair the evidence of a water problem (loose tiles, damaged floor, wet crawl or under floor area) by replacing finish flooring before the cause of water is correctly diagnosed and cured.
Questions & answers or comments about how to determine the extent and history of basement water leakage at a building.
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