Wet Basement Diagnosis & Cure: How to Inspect for Basement Leaks or Moisture
InspectAPedia^®  -      

• How to Inspect for basement or foundation leaks, basement or crawlspace moisture, a first step in fixing wet basements and indoor moisture or mold contamination
• How does curing a wet basement fix attic condensation, high indoor moisture and leaks, mold or indoor air quality problems in buildings?
• Photo guide to clues indicating sources of foundation leaks, basement leaks, water entry, high moisture
• Questions & answers about how to determine the extent and history of basement water leakage at a building

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.[4]

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 (see EFFLORESCENCE, Salts & White / Brown Deposits), in most cases in most parts of the world, building water entry in a crawl space or basement is due to actual water leaks, not rising damp.

Preventing rising damp: builders constructing masonry foundations and perhaps aboveground masonry walls in an area where rising damp is also a concern usually address the problem by including a layer of moisture-resistant materials in the masonry wall just above ground level as the wall is being built.

Preventing building water leaks & wet basements: we describe common water entry or leak points in basements and crawl spaces as part of our discussion of both ATTIC LEAKS Moisture or Mold (where did that moisture originate?) and also WATER ENTRY in buildings (how to keep a building dry and at proper moisture levels).

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 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.

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.

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.

Carson Dunlop Associates' sketch (above-left) illustrates how efflorescence is deposited on building interior walls. Details about this moisture or leak clue are at EFFLORESCENCE, Salts & White / Brown Deposits.

Watch out: as we demonstrate at MOISTURE METER STUDY, using infrared scanners will not reliably detect old or historic water entry leakage if the leak area happens to be dry at the time of the scan. A similar limitation applies to use of moisture meters. Evidence of moisture is a reliable indicator, but absence of moisture is not - moisture may be present but beyond the ability of the instrument to reach, such as a wet inner surface of exterior wall sheathing.

2. Wet conditions in a building: some limited areas of a basement or crawl space floor have been or are regularly wet or showing puddles in some weather conditions, but water does not extend over the entire building floor.

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.

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.

In the photograph shown here our client points to moisture stains originating high on a masonry block basement wall. 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. See ATTIC CONDENSATION CAUSE & CURE

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.

Simply cleaning up or removing attic mold such as moldy roof plywood, framing, or mold contaminated attic insulation may not provide a lasting cure for attic mold.

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.

Actual

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 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 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.

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.

Often, including at this building, the leaks at the concrete wall cold pour joint occurred primarily, or in this case only, where there was a concentration of water spillage outside the building. 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.

Our photo (left) shows stains at a poured concrete foundation wall crack that had been covered by insulation, drywall, and paneling in a finished basement.

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.

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.

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.

• 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 ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.