November, 2006
Inspection News and Views from the American Society of Home Inspectors

Keeping Basements Dry


If there’s a basement in the house you’re inspecting, almost all buyers want to know if it’s dry and if it will stay dry. Since most basement damage occurs slowly, over many years, it’s easy for home inspectors and for homeowners to overlook a problem unless there is evidence of a water leak or a major crack. To spot problems, home inspectors learn about the basic drainage and sewer systems. When home inspectors can explain these systems to their clients and provide information on the routine maintenance that helps keep basements dry, they are adding value to their service.

Homebuyers are often unaware of the most basic systems in a home; therefore, it may be helpful to provide background information as you explain the systems protecting a basement, how they work and how to maintain them.

There is nothing more basic than sewers. They drain water away from a house, and most larger municipalities have two types, each built for a specific purpose. Sanitary sewers carry waste from sinks and bathroom fixtures to the sewage treatment plant. Storm sewers collect rain and surface water and carry it to lakes or rivers.


Some houses have a foundation (basement) drain tile system that is connected to the storm sewer or to the combined sanitary sewer. Combined sewers? Yes, older systems may have “combined” sewers in which sanitary and storm sewers are combined in the street or below the house. Most of these systems are being renovated to keep surface water out of the sanitary sewers. We don’t want to pay to treat rainwater, and we don’t want it flooding our sewer plants. Nevertheless, many combined systems still exist. Some cities like Milwaukee install a deep-tunnel system to collect excess water from the combined sewers to help eliminate overflows into rivers and streams. The water in the deep tunnels is held and treated later.


The basement is connected to the sanitary sewer system at the floor drain or at basement plumbing fixtures. The system carries waste out of the house. As it reaches the street, the flow may travel downhill, aided by gravity, or it may be assisted by pumps. In either case, its final destination is the sewage treatment plant.

The storm sewer is connected to the sewer grates in the street and eventually dumps the clear water (rainwater) into rivers and streams. If a sump pump is connected to a sewer line, it should be connected to the storm sewer. Downspouts and rain gutters that are routed into underground sewer lines should also be connected to the storm sewer. Some sump pumps will be routed to the surface soil; eventually the water flows to the storm sewer.


Older homes–No drain-tile systems
Homes built around 1920 or earlier may not have drain-tile systems. These homes were often built “high on the hill” with a shallow basement that simply depended on surface grading to divert water from the basement.


Drain tiles, bleeders and damp-proofing
Homes with drain-tile systems share common components that collect and remove water. Exterior drain tiles are placed near or above the footings. These exterior tiles should be covered with at least two feet of gravel, allowing water to flow to the tiles. Older homes have concrete tiles; newer homes use perforated plastic pipe. Interior tiles receive water from exterior drain tiles via bleeders through the footings. Interior tiles route the water to a sump pump or palmer valve. (More about the palmer valve later.) To keep water out of the rest of the basement, a thin coating of tar or damp-proofing is applied to the outside of the foundation when the house is built. Block basement walls are “backplastered” with a thin concrete coating on the outside, under the damp proofing.


Homes built circa 1920 to 1950 – palmer valves  
Early drain-tile systems in some municipal areas (Milwaukee included) often were connected to the basement floor drain with a one-way check valve called a palmer valve. Some municipalities require that this connection be eliminated because it drains storm water into the sanitary sewer. If a palmer valve is present, it should open freely to discharge water. The homeowner will need to maintain the valve to prevent water from backing up.


Homes built after 1950 – sump pumps
Newer homes have a sump pump that removes the storm water from the drain-tile system and pumps it to an underground storm-sewer line or to the surface soil.

Rural homes – Septic systems, basement drainage
A home with a septic system simply has a private sewer-
treatment system. All the other principles of drainage are the same. Because the septic system’s drain exits the basement near the midpoint of the wall, the house may have a second pump crock to lift sanitary sewage from the floor drain and laundry tubs up to the septic-drain line. Homes in rural areas don’t have storm sewers. All storm water is routed to the surface and to ditches.


If the sanitary sewage system backs up, the basement could be affected. The sanitary system can back up because of a blocked pipe coming from the house or a blocked pipe in the street, or because the combined or sanitary sewers are blocked or overflowing.

When the sanitary or combined sewage system backs up, sewage will enter the house through the floor drain or any plumbing fixture. When a whole neighborhood experiences a sanitary sewer backup, it’s because a major sewage line is blocked or has more flow than it can handle. For instance, during a heavy rain the combined sanitary and storm sewers may be unable to handle the sudden increased flow.

Inspecting sewer lines is a specialized service requiring specific equipment. It is beyond the scope of a home inspection. Inspectors may choose to note for their clients whether or not a sanitary sewer clean-out is present, if clean-outs are customary in the local market.

There is little a homeowner can do to prevent a neighborhood-wide sanitary sewer backup except to work with the local municipality to correct sewage system problems.


Poor surface drainage or problems with gutters and downspouts invites rainwater into the basement. Drainage system are not designed to handle excessive surface water. If water floods around a basement, water will come in.

Water from the sump pump
If a sump pump is present, its job is to collect the water from the basement drain-tile system and discharge it. Water can back up from the sump pump if the electrical power goes out, the flow is too great, the discharge is blocked or the pump malfunctions. Storm water may overflow the sump pump crock, run down the floor drain into the sanitary sewer and/or flood the basement. If the pump has a switch that can be triggered by hand, then test it during the inspection to make sure that the pump is working.


Water from the walls, window wells, cracks and floors
As discussed, water may leak into a basement because of poor surface grading or problems with gutters, downspouts and sump pump discharges. Leaks can also be caused by problems with the palmer valve, drain tile, storm-sewer lines or window wells.


Most basement seepage problems can be avoided or solved by following these simple corrective steps, which are listed in order of priority.

1. Keep gutters and downspouts clean, and direct them away from the basement.
Downspouts must be routed to a storm sewer or at least six feet away from the foundation to an area where the water will flow away naturally.


2. Grade soft surfaces. All surface water must flow away from foundation walls. Soil should pitch away from the basement, dropping six inches for every six feet. The soil under any bark or stone mulch around the house must pitch away; ideally, any plastic under the mulch will pitch away, too. Check under decks and porches. During a heavy rain, walk around the house to check for pooling water. No water should pool around or flow toward the basement walls.



3. Grade hard surfaces.
All concrete and asphalt surfaces must pitch away from the basement. Watch for slab concrete beneath decks. Check all stoops, drives and walks.


4. Grade the soil around window wells to direct water away. Seal the window well tightly to the foundation, and keep the inside of the well clean. The inside of the window well should have a base of six to 18 inches of gravel—not mud. Also, the window well may have its own drain or should flow into the exterior drain-tile system through the gravel base.


5.  Check the palmer valve. This check valve must swing open easily to drain water from the drain-tile system. If it is stuck closed, water may back up in the basement, and, eventually, the drain tiles will become plugged with debris. Use a wire to hook the bottom of this round flap valve; it should swing upward on a hinge at the top of the disk. If the valve is stuck, free it with penetrating oil and a pry bar.

6. Check the sump pump. The float must move up and down easily to activate the pump. If the float sticks, there will be a flood. Make sure the pump is secure and will not allow the float to stick to the sides of the crock or the cover. Lift the float to check that the pump will remove water from the crock; the pump should switch on when the float is eight to 12 inches from the top of the crock. If the pump allows higher water levels than this, seepage near the floor may occur. Replace a sump pump that is old and worn. If the pump runs often, have a spare sump pump handy.

7. Look for gaps and cracks in joints. These can allow water to seep next to the basement. The gaps can be filled with a backer rod and concrete joint filler.

8. Check for cracks in poured concrete walls or block walls. These should be evaluated and patched by a professional.

9. Check for problems with underground storm drain lines. If damp spots and seepage appear near a sump pump or downspout storm sewer line, the problem may be a broken or plugged underground line. You can test this line by running water into the pipe with a hose and watching for seepage in the basement. You can also temporarily abandon the underground line and route the sump pump or downspout to the surface, well away from the home. If seepage no longer appears in the basement, you’ll know the problem is a broken drain line.

10. Investigate underground water supply lines. If seepage occurs near the water main into the house, suspect a broken underground water line.

11. Investigate all homeowner-installed underground drain lines.
Often, they are unable to withstand freezing because they are installed too near the surface and/or they’re made of improper materials, easily broken by frost. Also, many such lines can’t effectively carry water away from the foundation because they have poor pitch or are undersized. Temporarily abandon these lines to test them. If you see water bubbling up from connections to these lines, there is a problem.


12. Watch for roots in the sump pump crock. Roots inside the crock mean there are roots in the bleeders and in the outside drain tiles. An expert should evaluate this problem.


• Active water leaks near the basement floor indicate problems with drain tile and surface drainage.

• Active water leaks higher on the wall usually indicate a surface water drainage problem or a broken drain or supply line. A problem with window or door flashing, window sills, a roof leak or brick veneer also could cause a leak on a basement wall.

• Efflorescence or salt stains indicate that water is pushing through the masonry surface and depositing these white or tan salt stains.

• Water stains, damp spots, mildew and chipping/ splintering of masonry indicate that water is pushing through the masonry.

• Dampness, odor, mold, mildew and condensation indicate that water is pushing through surfaces or leaking into the structure. High levels of moisture in basement air also can cause these problems.

• Wood rot, wood movement and stains on wood and drywall indicate leaks and moisture behind finishes.

• Cracks and wall movement may indicate an unstable foundation wall, often caused by drainage problems.

• Damp walls and floors with a dry sump pump crock indicate a drain tile problem.

• Roots in the sump crock indicate a potentially serious drain-tile blockage and drainage problem.


Continued seepage may indicate damaged or missing drain-tiles, but the interior and exterior drain-tiles should always be evaluated before a major repair is started. The test costs approximately $400.

An interior drain-tile test involves cutting several holes in the basement floor to expose the interior drain tiles and bleeders in several areas so they can be inspected for debris and water flow.


Exterior drain-tiles can be tested with a “water spud.”  This is a small-diameter pipe that looks like a tree root fertilizer tool. The pipe is inserted in the ground next to the foundation. Water is forced into the ground through the pipe and the flow is traced into the drain-tiles. If tiles are blocked, water will appear on the basement walls and at the wall/floor joint.


Leaks associated with wall and floor cracks usually cannot be solved by normal maintenance. Inspectors who are qualified to do so may advise clients on the repair methods available for these types of problems.
Even when a basement is bone dry with no signs of future problems, home inspectors do their clients a favor by sharing the simple maintenance steps that can help prevent small problems from occurring and eventually escalating into serious damage.