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    Basement Flooding & Solutions

    Basement Construction

    Many basements are designed as shown below. Footings are laid or poured on a gravel bed and designed to support the weight of the building. Walls support the upper stories. It is important to note that basement walls and floors are typically built only strong enough in the sideways direction to hold back the dry dirt that surrounds the basement . After a while all houses settle, particularly those on unstable soil. Settling results in some cracks in basement walls and floors.

    fig 1

    Typical Basement Construction
    Figure 1

    When water comes in contact with the walls or floor, it may leak through the cracks that have formed and get into the interior of the building. If there are no cracks big enough to permit the water to go through, water may build up outside the walls. The deeper the water level, the greater the water pressure will be on the walls and floor.

    One consideration is the "head" of water that threatens the basement. "Head" is the height of water above a specific level, such as your basement floor. The greater the head (ie. the deeper the water), the more water pressure there will be. Studies by the U.S. Army Corps of Engineers have concluded that typical basement walls and floors are not built to withstand water pressures on the outside of the walls from a head greater than about three feet deep.

    Construction practices now take such ground water pressures (and basement dryness) into account. Subsurface drainage systems ("foundation drains") are installed to reduce the amount of groundwater against the basement walls. As shown in Figure 2, drain tiles are laid at the base of the basement walls, outside of the building. Sometimes, drain titles are also laid underneath the basement floor near the footing. If there is a location on the lot that is lower than the basement floor, these tiles are sometimes run out to the low spot, allowing gravity to take the water away from the building. Of course, many times the slope of the lot does not allow gravity to handle the situation. In those cases, a sump needs to be installed to collect the water from the foundation drains. The correct solution today is for there to be a separate sump pump which pumps this clean foundation drain water out of the building to a surface location that will drain away from the house, as shown in Figure 2, or into a storm sewer.

    fig 2
    Typical Foundation Drain Tiles & Sump
    Figure 2

    Housing areas older than 15 or 20 years may have foundation tiles connected to sanitary sewer systems that drain to the sewage treatment plant. However, this is not allowed today. The water collected by the foundation tiles is considered to be clean water. Today, clean water is banned from sanitary sewers because it may cause the sewer collection system, or the sewage treatment plant, to be overloaded during wet weather. Such overloads are the main cause of sanitary sewer backups into basements or sewer overflows into creeks and streams.

    The Federal Clean Water Act has made such sewer connections illegal; they need to be disconnected. Old foundation drains need to be modified by the addition of sumps, pumps and piping which direct this water out onto the top of the ground at a location that will drain away from the house as shown in Figure 2, or into a storm sewer.

    fig 3
    Sources of Basement Water
    Figure 3

    There are four ways water can get into your basement, as shown in Figure 3:

    1. Through the foundation drain system sump.
    2. Backing up through the sanitary sewer lines under the house.
    3. Through cracks in the walls and floor.
    4. Surface run off through windows and doorways.

    There are many ways to cope with these problems. Remember: you could be affected by a combination of two or more of these water problems. For example, when sewers appear to backup, you may not be able to tell whether there is seepage through cracks in the floor or whether the foundation drains are overloading your own (partially blocked?) sewer line to the main sewer line. Therefore, you should investigate all four of these possible sources of water and their solutions before you try to correct a basement water problem.

    Sump Backup

    The sump in your drainage system is directly connected to the drain tiles and therefore to the water in the ground outside your basement walls. A sump will backup when the pump fails, when the power fails, or when the pump is overloaded.

    The first condition can be prevented by proper pump maintenance and operation according to the manufacturer's owner's manual. This includes periodic cleaning of the debris screen, even during high water. A clogged intake is as good as having no pump.

    fig 4

    Figure 4 Typical Pump & Sump

    One of the most common causes of basement flooding is not pump failure, but electrical failure. Power losses often accompany severe storms. Backup systems with batteries or generators are available commercially and experienced flood victims will tell you they are well worth the cost.

    Safety Note: Be sure your backup generator exhausts to the outdoors. Just like your car engine, a gasoline powered generator creates deadly carbon monoxide gas.

    Pump overload occurs when there is more water coming into the drain tiles than the pump can handle. Several precautions can be taken. One is to have a second or even a third pump on hand. Each one should have its own discharge pipe. The most important precaution, however, is to be certain that the downspouts from the roof are not connected to the foundation drain tiles. This practice was common in some communities, but it is a bad idea for several reasons: downspouts can overload the sump pump and they can fill the foundation drain with debris such as leaves and twigs (which may also clog the sump pump.) Another precaution to minimize foundation drain sump water is to make certain that the surface of the ground near the house slopes away from the house.

    Make sure the sump discharge pipe drains on top of the ground, well away from the house. To avoid using your pump to recirculate the same water, the discharge should be located at a point that drains rapidly away from the house. The Clean Water Act no longer allows sump pumps to drain into the municipal sewer system because they overload the sewers or treatment facilities. Furthermore, such a connection could contribute to sewer backup problems discussed in the next section.

    In some communities, homeowners are encouraged to connect the sump pump directly to the storm sewers. This may cause a problem, however; if the storm sewers backup, they can flood your house through the sump. To avoid this, install a check valve as shown in Figure 4.

    Sanitary Sewer Backup

    Sewer backups can be caused by either a problem in your line or an overloaded sewer system. The thing to check first is whether the sewer line on your property (known as a "lateral") is broken or clogged with roots or debris. If you flush a toilet or the washing machine drains and water backs up into your basement, you know the lateral has a problem because it cannot carry the large volume of water that a typical home produces from time to time. If this is the cause of your flooded basement, you can fix the problem relatively easily. "Rod out the line" and repair the break. Consider repairing your broken pipe with something more sturdy. If help is needed, contact a plumber or contractor. They could help you to diagnose your lateral situation, too.

    fig 5

    Broken Lateral with Clogging Roots
    Figure 5

    If your line is okay, the problem may be that the sanitary sewer system cannot handle the high volumes of water that come with heavy rain or flooding. Blocked pipes, too many ground water connections, or some other reason may overloaded and backup the sewer mains, perhaps high enough to come into your basement. If you feel that the water in your basement is sewage, contact the public agency in charge of the sanitary sewers near your home and inform them of the problem. The Montgomery County sewer service areas are shown in Figure 10.

    There are four ways to protect against this type of backup: install a plug, a standpipe, a check valve, or an overhead sewer.

    Plug: Since the basement floor drain is the lowest point in your house, it is the first place of entry for backed-up sewage. The drain can be closed with a rubber or wooden plug during heavy rains. Some drains are threaded for a screw-in plug. Plugs can usually be bought at a hardware, building, or plumbing supply store.

    This is the simplest and cheapest way to stop sewer backup. However, the sewer could backup into the next higher opening, probably a sink drain or toilet.

    Standpipe: A pipe inserted or screwed into the floor drain will allow the sewer backup to seek its own level without flowing into your basement. Such a standpipe probably needs only to be tall enough to be a little higher than street level. Higher water would then flow out of the municipal lines into the street.

    fig 6

    A Temporary Standpipe Can Contain the Sewer Backup
    Figure 6

    A standpipe may be more dependable than a plug that could pop out. However, it has the same shortcomings as a plug: you have to be home to put it in, if the water keeps rising, it will overflow out of the next higher opening, and there is still pressure in the line.

    fig 7

    A Valve (Check or Manual) on the Lateral Can Prevent Backups
    Figure 7

    Check Valve: A check valve installed in the sewer line is more expensive, but it will prevent the sewer backup into your basement as long as it is kept clean. Valves can be jammed open by debris. The valve should be placed where it would be easy to maintain. Check valves and manual valves have been known to "freeze up" if they are not maintained periodically. All types of valves should have a manhole or other access so they can be cleaned out or repaired. Because such a valve closes your lateral during backup times, you cannot drain household sanitary water unless you have a bypass sanitary pump.

    Overhead Sewer: Your basement sewers can be rebuilt so that all basement sewage drains to a sanitary sump. All basement sanitary sewage would then be pumped up to the height of the basement ceiling. From this height, it would flow by gravity into the lateral and out into the sanitary mains. Even in the rare event of sanitary sewer main backups, the water would not be able to backup into your basement through the lower level floor drains. In the case of a power failure, you would simply refrain from using any basement plumbing. Upstairs plumbing could continue to be used, even in the event of a power failure. If the basement doesn't have much in the way of sanitary facilities such as toilets or showers, this conversion to a sanitary sump can be quite inexpensive.

    fig 8


    Heavy local rains, water standing in your yard, or surface flooding, can cause the ground around your house to become saturated with water. Cracks in your basement walls or floors will then allow seepage of water into your basement. The exact location may be difficult to ascertain if the basement walls are covered with paneling or drywall.

    The best way to deal with seepage is to relieve the groundwater through subsurface drain tiles and ensure that the walls are waterproofed. Cracks can be repaired and the walls can be waterproofed from inside or outside. Waterproofing on the outside of the wall is more effective because groundwater presses the sealer into the walls. The best technique is to dig a ditch around the basement wall and apply a sealant. This can be done by the handyman (many home maintenance manuals have instructions for this) or a commercial waterproofing company. In either case, ask the supplier or company to provide references of area buildings that have used their technique or materials. Because the work is hidden and sloppy work may not appear for several years, there have been instances of contractors doing poor basement waterproofing. It is also important to make sure that any newly installed basement foundation drains empty freely and that porous fill is used against the basement wall over the drains in order to direct any groundwater to the drains.

    A foundation drain tile system has proven very effective in dealing with such groundwater. Water is kept away from the basement walls by draining down to the drain tiles. The groundwater then flows to the clear water sump and is pumped out. This foundation drain water should never be connected to the sanitary sewer system, however, because it can overload the sewer mains and cause sanitary sewage backups into neighborhood basements.

    Surface Flooding

    The most serious type of damage to your basement may come from floodwaters on top of the ground. This may be caused from overflow of a nearby stream or, if your building is unfortunately located in a low spot, from the concentration of area runoff from heavy rains.

    One of the first responses to this sort of flooding is to seal up the openings such as the windows. This can be done by replacing windows with glass blocks or raising window wells above the likely outside water level. A low wall can be built around stairwells. The safest approach is to keep the surface water away from the building. As long as floodwaters do not directly touch the building, the water will take time to seep through the ground and you can deal with it as you do with regular seepage.

    fig 9
    Slope the Ground Surface Near the House, Away from the House
    Figure 9


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