These pages offer practical information that will help you flood proof your home. They will help you understand the causes of basement flooding as well as find solutions. 

 Let’s begin with a brief introductory exercise to become familiar with flood proofing terms. See if you can match the following descriptions with the numbers on the illustration (answers are at the end of the glossary):

  1. ___ the undisturbed soil around the backfill zone;
  2. ___ downspouts that extend beyond the backfill zone with splash pads;
  3. ___ the backfill zone;
  4. ___ soil around the house that is sloped away from the foundation;
  5. ___ the sump pit and pump;
  6. ___ the backflow valve;
  7. ___ the weeping tile.
Also shown are the domestic and storm sewer underground pipes. The storm sewer (which carries rainwater) is the larger pipe. The domestic sewer is the pipe which connects to Edmonton homes. In most cases sewer backup happens after rainwater overfills the domestic sewer.

An Example of Good Flood Proofing Practices

Why Basements Flood

Hundreds of basements flood each year because of poor backfill methods, clay, faulty roof top drainage, foundation drainage or disposal of storm water in the domestic sewer.


The Backfill Zone

When a new basement nears completion, soil or backfill is pushed into the gap between the basement wall and the clay walls of the open excavation. The illustration shows the basement wall, the backfill zone and undisturbed soil.

The Backfill Zone

In most cases, backfill material is reused soil. Likely, it is the same soil that was removed to create the excavation. Upon removal, something new is added to the soil: air. This is not good. The air-soil combination becomes backfill that has empty spaces or voids. As a result, the soil will continue to settle for years.

Even after a few short years, you can see where the soil has settled, but may not be able to see depressions hidden by decks, stairs or patios. During rains, low areas become puddles next to the foundation.

To combat this problem, clay soil is recommended as a cap for the backfill zone (shown in the illustration). Top soils or sandy soil are not recommended. They allow water to percolate down into the backfill zone. But if you want a flower bed around the perimeter of the foundation, start with a clay base 8 - 10 inches thick. Slope the clay so that water will drain away from the house. Extend the clay 6 - 8 feet out from the house. Decorative landscaping materials or a flower bed may then be added.

Our heavy clay soil contributes to basement flooding in two ways. First, by blocking the flow of water away from the backfill zone and second, by swelling and cracking concrete walls and floor. Water trapped between the basement wall and the undisturbed clay soil may eventually seep through the basement wall. Or, as the clay soil gets wet and swells and then dries, powerful forces crack basement walls and floors. The following example explains this concept.

Referring to the first frame of the illustration, we see a large hole or excavation much like a swimming pool. When filled with water, the undisturbed clay soil swells and expands, creating a barrier that could retain water for weeks.

If, instead of digging a swimming pool we were to excavate a new basement, the same reasoning would apply. Any water percolating into the soil on the outside of the walls would remain trapped within the backfill zone as shown in the second frame. With time, rainwater or snow melt could soak into the backfill zone.

The third frame of the illustration shows unwanted water in the backfill zone. Powerful pressures from swelling and shrinking clay soil crack the concrete walls and floor. Cracks become pathways for water to enter the basement.

So we see that water entering the backfill zone either seeps into the basement or enters through cracks in the concrete.

Preventing water from entering the backfill zone is the answer.

Stop Rain and Snow Melt From Cracking Your Basement


Rooftop Drainage

Much of our modern cityscape is impervious to water. Streets, parking lots, driveways, sidewalks and even rooftops shed rainwater. Consider that one inch of rain falling on a 1200 sq. ft. bungalow produces 600 gallons of water. Where does the water go?

Eavestroughs catch rainwater and downspouts carry water from the rooftop to the ground. Downspouts that are too short will pour rain water directly into the backfill zone as shown below. Soil erosion and water in the backfill zone are consequences of short downspouts.

Downspout Too Short

If downspout extensions are in place, as shown below, rainwater is discharged beyond the backfill zone. By combining a splash pad and downspout extension, a drier basement can be expected.

Correct Downspout Extention with Splash Pad

A few homes still have downspouts conveying rainwater to the storm sewer via a plumbing stack in the basement. Homeowners should redirect the downspouts so that the water is discharged to the yard with proper extensions and splash pads. Once downspouts are redirected it is advisable to cap storm water stacks to prevent sewer back-up through this pipe.

But what if rainwater does enter the backfill zone? Where will it go? How can it be disposed of to avoid structural or in-basement property damage? The modern answer is a foundation drain or weeping tile system.

Weeping Tile (Foundation Drainage)

Edmonton home builders have been installing weeping tile since the early 1960s. Commonly referred to as foundation drains, these underground water pipes offer an escape route for water collecting under houses. When water percolates through the backfill zone along the outside of basement walls, it collects in the weeping tile. From there it flows by gravity to the sump pit.

Rainwater entering weeping tile varies from house to house. Weeping tile flow ranges from a few teaspoons to hundreds of gallons per day. Strongest flows usually happen during spring melt or from a long rainstorm.

To help you visualize your foundation drain, consider the following step-by-step description for new home installation of weeping tile. Illustrations correspond with each step. The illustration enclosed in the circle (on left) is a magnified view from the bottom edge of the excavation. The illustration on the right is the excavation or site where the basement will be built.

1. A backhoe (large earth moving equipment) is used to dig a hole for the basement to rest in. The size of the hole or excavation should be as small as practically possible, yet allow room for work crews. The base of the excavation is to be as flat as possible.

2. A concrete footing is poured about 24 inches from the perimeter of the excavation on undisturbed soil. The footing is where the basement walls and floor will rest.

3. Weeping tile is a six inch plastic pipe with small holes throughout. It is tucked against the footing (not on the footing) and placed around the entire outer edge of the footing and leads to the sump pit. A 1200 sq. ft. house would require 150 feet of weeping tile.

4. After the basement wall is poured on top of the footing, as shown below, a layer of coarse gravel is placed between the undisturbed soil and level with the top edge of the footing.

5. Finally, soil is pushed into the open hole covering the weeping tile and filling the space between the foundation and the edge of the excavation. Again, this soil is referred to as backfill and, when complete, the backfill zone.


Sewer Backup or Sewer Surcharge

Rainfall and snow melt waters can overfill the domestic sewer. Consequences include: sewer backup, untreated sewage overflow into the river and extra handling and treatment costs. Why and how is this happening?

Examine the illustration which shows House A. Note water percolating through the backfill zone to the weeping tile, sump pit and finally into the domestic sewer. Rainwater has taken up space in the underground sewer pipe. That space was meant for sewage, not rainwater. When the pipe is over filled like this, it is called sewer surcharge.

Rainwater... to weeping tile... to domestic sewer

Next examine House B, shown on the next page. There is no water in the backfill zone but sewer backup is happening. Likely House B is in another neighbourhood, yet rainwater from House A is contributing to sewer backup at House B.

Sewer Backup

Protecting your basement from sewer surcharge is important. What about your neighbour’s basement or your neighbour’s neighbour? The volume of weeping tile water from one home is small, but when 10 or 20 or even 30 thousand homes dispose of weeping tile water in the domestic sewer, a more serious problem develops.

Combating sewer surcharge may involve some or all of the following in-basement actions: installation of a sump pump, installation of a backflow valve and permanent disconnection of weeping tile water from the domestic sewer.

Equally important are actions that can be taken in the yard. Sloping soil from the foundation will drain rainwater and snow melt away from your basement. Checking and cleaning eaves and downspouts will ensure they discharge properly to a splash pad.

Each year in Edmonton, thousands of gallons of clean rain and snow melt enter the domestic sewer unnecessarily. Rainwater or snow melt is transported to and processed at the sewage treatment plant. Instead, it could be pumped from sump pits onto streets where it would run off into a storm sewer and then to the North Saskatchewan River.

Pump weeping tile water out of your basement onto your yard. While there are other options, a properly installed sump pump is a positive step to reducing the risk of sewer backup in your home and other homes in Edmonton.


Flood Prevention Strategies

When you begin to flood proof your home, you may wish to consider two approaches: comprehensive flood proofing or prioritized flood proofing.


1. Comprehensive Flood Proofing

This concept is an all-encompassing approach to ensure a dry basement. It involves taking action to keep water out. It includes the following: Comprehensive flood proofing is the most thorough approach. It offers the best measure of protection from basement flooding. Cost is less of a consideration.


2. Prioritized Flood Proofing

In this approach, a diagnostic process is used to identify flood water sources. Once these sources are verified, the most cost-effective plan is devised to stop water from entering the basement.

Whichever approach you decide to adopt, the more effort taken to diagnose basement flooding problems, the lower the cost and the better the solution.

The next section introduces ways to diagnose basement flooding problems. Before moving into this section we discuss briefly how to locate your sump pit. It is really the starting place when flood proofing.


Flood Proofing Actions

Locating Your Sump Pit

Does my house have weeping tile and a sump pit? To answer this question you must locate your sump pit. Look along the basement wall facing the street as shown below in the illustration. Or if you live on a corner lot, check along both walls that face the street.

Locating Your Sump Pit

In basements with finished flooring, the sump pit may be hidden under a plywood cover. To locate the sump pit, tap a broom handle along the floor until you hear a hollow sound. The hollow sound indicates a covered opening in the basement floor. Most sump pits are about 18 inches x 18 inches x 24 inches deep. There may be several openings, so check until you find a hole of the size described above. Likely, there will be capped pipes, open pipes and possibly a sump pump.

Once you find the sump pit, you can check for several things:

  • Is it wet or dry? Depending on the season, the pit may have water or be bone dry.


  • Is there an open pipe about four inches in diameter on the side of the pit? If so, then this is likely a weeping tile outlet. Again, this is a good indicator that your home has weeping tile.


  • Is there a P-trap in the sump pit? This is a two-inch plastic drainpipe on the bottom of the sump pit.
    Water entering the sump pit drains through the P-trap into the domestic sewer. Most often, the open end of the P-trap is threaded to receive a cap.


  • Is a P-trap cap available? During a major storm or an extended rainfall, the cap should be in place to protect against sewer backup.

If you thread-in the P-trap cap during a storm, bear in mind that the weeping tile will continue to flow. You will need to check the sump pit water level frequently to ensure it doesn’t overflow.


A sump pump will start automatically. Save yourself a sleepless night of bailing. Install a sump pump now!
Remember, weeping tile water is just water that has made its way through the soil into the sump pit. A properly functioning sump pit includes a sump pump that will move weeping tile water outside the house, where it can drain from your yard into the storm sewer. In so doing, rain or snow melt is not overloading the domestic sewer and contributing to the flooding of someone else’s basement.

Diagnosing and Solving Flood Problems

The following section presents common flooding situations in a problem, symptoms, causes and solutions format. In some cases a general description, offering more in-depth comments, is also included.

1.Problem: Water entering at the basement walls and concrete floor
Symptom: Wet carpets and floors along basement walls.
Cause #1
Downspouts are too short and water is percolating through the backfill zone.
Solution #1: Extend downspouts so that they discharge rainwater at least six feet from the foundation onto a splash pad.
Solution #2: Position a rain barrel so that it will catch rooftop water. Be sure to have an overflow spout so that water is discharged away from the foundation as described above.
Cause #2
Downspouts and/or eavestroughs are clogged and rainwater is spilling onto the ground around the foundation and percolating into the backfill zone.
Solution #1: Clean and leak proof eaves and downspouts each spring.
Solution #2: If your eaves are clean and working well, yet water is still spilling over, there may be another problem. If the underground yard pipe is buried, it may have become blocked with roof debris. Disconnect your downspout the next time it rains. If there is a sudden, strong, steady flow that quickly slows after a few minutes, the underground yard pipe is plugged. You may wish to redirect the downspout to the surface. This will require adding an extension and splash pad.
Cause #3
Low spots on the backfill zone are allowing water to pool next to the foundation.
Solution #3: Add soil over the backfill zone, sloping it away from the foundation. Remember to pay special attention to areas under decks, steps and other covered or hidden areas. Often, these areas are neglected yet contribute to wet basements.
General Comments: Clogged downspouts and low areas next to homes commonly contribute to basement flooding in Edmonton. They may require attention every few years. Routine maintenance, combined with sound flood proofing practices, will keep water out of your basement.

Diagnosing and Solving Flood Problems

2.Problem: Water entering the basement from under the basement floor from the sump pit (no sump pump is installed as shown below).
Symptom: Water flowing from sump pit onto basement floor or heaving basement floor.

Typical Sump Pit

Water being collected by the weeping tile is accumulating in the sump pit with P-trap cap in place as shown on the previous page.
Solution #1: Remove the P-trap cap to drain water from the sump pit into the domestic sewer.
Solution #2: If you are unable to remove the P-trap cap and weeping tile water is filling the sump pit, handbailing is another way to dispose of the rainwater.
Solution #3: Install a proper sump pump to move water outside the house and away from the foundation, as shown below. This is the recommended solution.

 If the domestic sewer is surcharged, you risk sewer backup by removing the P-trap cap.

Typical Sump Pit With Pump

General As a rule, P-trap caps should not be threaded into place unless your home is equipped with a properly functioning sump pump. Homeowners who have a properly functioning sump pump, P-traps in place, and close off any floor drains during and after storms can expect to have a high measure of flood protection.

Diagnosing and Solving Flood Problems

3.Problem: Water enters the basement from the sump pit (sump pump in place).
Symptom: Water flowing onto the basement floor out of the sump pit.
The sump pump has failed.
Solution: Should you want to service the sump pump yourself, the following is a list of things to check:
  • Is there electricity to the pump?
  • Are the floats stuck? (submersible pumps don't have floats)
If your basement is flooding with weeping tile water, replace the sump pump as soon as possible. A call to a plumber may be the quickest answer. Replacing the failed pump with a new one is also an option. Meanwhile, if your basement is flooding, you may need to hand bail the sump pit to prevent overflow.

Another option is opening the P-trap by removing the cap. Remember, if the sewer is surcharged, there is a risk of sewer backup in addition to the weeping tile flooding.


 Exercise extreme care when around the sump pump, your contractor will be working with electricity near water. Have your consultant insure that the contractor follow the instruction manual supplied with the sump pump. 
General Discussion: Sump pumps contain parts that may be continually submersed in water. Rust and small soil particles can damage the pump. Regular inspection is important. Servicing the sump pump every few years will ensure it is ready to function when needed.

Diagnosing and Solving Flood Problems

4.Problem: Sewer backup entering at basement floor drains.
Symptom: Sewage flowing from floor drains and basement plumbing such as toilets, showers and washing machine standpipes.
Too much storm water or snow melt in the domestic sewer is causing the sewer to back up.
Solution #1: Thread in all basement floor drain caps, including the P-trap. Also, close the gate valve. This is usually a large, red handled valve. Sometimes it is recessed in the floor. In developed basements the gate valve is often hidden between walls or under a sink vanity. If sewage is coming out of the floor drains, close the gate valve until the flow stops. A gate valve is opened and closed manually by hand cranking. The gate valve protects only the plumbing connected to that pipe. Remember to open the gate valve after the storm has passed.
Solution #2: Install a sewer backflow valve as shown in the illustration below. This prevents sewer backup from the domestic sewer, automatically preventing raw sewage from entering your home. A sump pump will automatically discharge weeping tile water from the sump pit to your yard. Not only will weeping tile water be removed from your basement but it will not contribute to overloading the sewer and potentially enter other basements. The overall impact of widespread use of sump pumps in Edmonton is a lower risk of sewer backup around the city. A sump pump and backflow valve combination offer a high level of basement flooding protection.
 Some automatic backflow valves require venting. Discuss this with your Consultant.

Suggested Backflow Valve Placement

Diagnosing and Solving Flood Problems

5.Problem: Your sump pump operates continually, but doesn’t move much water.
Symptom: Only small volumes of water are pumped and the sump pit water level hardly drops; but the sump pump works constantly.
No check valve is in the sump pump discharge pipe. Without a check valve, water flows back down the discharge pipe into the sump pit, partially refilling it and initiating another pump cycle.
Solution: Inspect the sump pump to see if there is a check valve in the pipe. Check valves can be located just above the sump pump or near the basement ceiling where the pipe passes through the house wall. Two check valve locations are shown at points A and B on the illustration below.

Suggested Backflow Valve Placement

Diagnosing and Solving Flood Problems

6.Problem: The sump pit overflows quickly during a power outage. 
Symptom: Water flowing onto the basement floor from sump pit.
The sump pit is too small to contain the weeping tile water until the power comes on again.
Solution: Enlarge the sump pit to handle a two-hour power outage. The sump pit should have a water storage capacity of 60 gallons. 

 Recommended minimum dimensions are:

Length:        24'' 
Width:         24'' 
Depth:         30'' 

Setting Your Plan In Motion

Planning to do it yourself?

Even the best "do-it-yourselfer" can always use a little bit of assistance and advice. So, while making plans to flood proof your home, please consider the following.

        Hire a Qualified Consultant

        Remember, you must obtain a City of Edmonton Building Permit if you intend to install a backflow valve so that the City of Edmonton can inspect the work to ensure that the job has been done according to the Plumbing Code. A permit is not required for adding a sump pump.

Professional Flood Proofing Services

EnerMac Consultants Inc. recommends that you treat flood proofing services like you would any other major purchase. Remember to hire a Consultant that will: Local contractors are equipped to assist you with your flood proofing requirements. The following categories of service providers may be some of the  flood proofing  expertise brought in by your Consultant:

Flood Proofing While On Vacation

If you are planning to be away on holidays, make arrangements with a trusted neighbour to monitor your home for potential flooding and list the following for their benefit:

Diagnosis Chart

Print out this handy form for your convenience

1 Flooding Symptom in Your House:
2 Probable Causes:
are too short
Downspouts blocked Weeping tile water held in sump pit Sump pump failure Storm water overload in domestic sewer Check valve missing Power failure with too small sump pit Weeping tile blocked
1. Wet carpet around edges of basement walls A,B C,D M
2. Clear water overflow from sump pit or heaving basement floor E,F,G,H H
3. Clear water overflowing from sump pit (sump pump installed) H
4. Sewer backup at floor drains I,J
5. Continual sump pump activity A D H K
6. Clear water flowing onto basement floor from sump pit A C E,F,G H E,F,L
7. Water ponding around house next to basement A C,D N

3 Solutions Chart:
(Yes or No)
Get Estimate Cost
A. Extend downspouts and add splash pads
B. Install rain barrel with overflow to splash pad
C. Clean and leak proof eaves
D. Disconnect downspout from underground yard pipe
E. Remove P-trap cap to drain sump pit
F. Hand bail sump pit
G. Install a sump pump
H. Service sump pump
I. Close all basement drains, P-traps, valves
J. Install backflow valve
K. Install check valve or sump pump discharge pipe
L. Enlarge sump pit to hold 60 gallons
M. Call professional foundation service company
N. Add soil around house to drain water away

Record of Home Service Activities

Print out this handy checklist for your convenience

Flood Proofing Maintenance

Eaves Cleaned
Downspout extensions checked and in place
Grade of Property Checked (sloped away from foundation)
Dates Checked
General Grade Around House
Under Deck
Under Back Step
Under Front Step
Under Sidewalks
Under Driveways


Sump Pump Maintenance

Installation Date :
Visual Inspection and Test:


Sewer Backflow Valve

Installation Date :


Flood Response Plan

Filed In:
Last Time Update:

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