What you need to build a sump pit

A sump pit is a hole dug below your basement floor where water collects before the pump removes it. You can build one yourself if your basement is dry enough to work in and your local code allows it — some jurisdictions require a licensed contractor. The basic structure is a hole, a basin or crock to hold water, and a pipe that carries water away from your foundation.

You will need a shovel or small excavator to dig the hole, a plastic basin or sump crock (usually 18 to 24 inches deep), PVC pipe for the discharge line, a check valve to prevent backflow, and a sump pump. The hole should be at least 2 feet deep and wide enough for the basin to fit inside with room to work around it. Dig in the lowest point of your basement, usually near a corner or along the foundation wall.

Key Takeaways

  • The pit itself is a hole below floor level with a plastic basin inside; the pump sits in the basin and pushes water out through a discharge pipe.
  • Dig the hole in the lowest spot of your basement, make it at least 2 feet deep, and check your local building code before you start — some areas require a permit or licensed installer.
  • A check valve on the discharge line prevents water from flowing back into the pit when the pump stops running.
  • The discharge pipe must slope away from your foundation and empty at least 10 feet away, or into a storm drain if your code allows it.
  • Once the pit is built and the pump is running, you will need to check the float switch and clean the intake screen every few months to prevent clogs.

Digging the pit in the right location

The location of your sump pit matters more than most homeowners realize. Water flows downhill and collects in low spots; if you dig your pit in the wrong place, it will sit empty while water pools elsewhere. Walk your basement after a heavy rain and look for where water enters or where the floor stays wet longest. That is where your pit should go.

The pit should be at least 10 feet away from your furnace, water heater, or electrical panel — you do not want to dig into utilities or create a safety hazard. If your basement has a floor drain already, the sump pit can go near it. Dig straight down until you hit gravel or bedrock; most basement floors sit 4 to 8 feet above the water table, so you should not need to go deeper than 3 feet. If water rushes in as you dig, your water table is high and you may need a professional assessment before proceeding.

Installing the basin and preparing the hole

Once the hole is dug, place the plastic sump basin or crock inside. These baskets come with a lid that has a hole for the pump discharge pipe. The basin should sit level on the bottom of the hole; if the floor is uneven, add a thin layer of sand to level it. The basin keeps sediment and debris from clogging the pump intake.

Before you set the pump in the basin, drill or cut a hole in the basin floor if it does not have one already — this allows groundwater to seep in from below. If the hole is too small, water will not enter the pit fast enough; if it is too large, sediment will clog the pump. A hole about 1 inch in diameter is typical. Backfill around the basin with the soil you removed, packing it firmly so the basin does not shift when the pump runs.

Running the discharge pipe away from your foundation

The discharge pipe carries water away from your basement and must slope downward the entire way — water will not flow uphill on its own. Use 1.5-inch or 2-inch PVC pipe, depending on your pump's outlet size. The pipe should leave your basement through the rim joist (the band of wood where the foundation meets the house frame) or through the basement wall, sloping down as it goes.

Outside, the pipe must empty at least 10 feet from your foundation. If it empties closer, water will seep back into the soil around your basement and defeat the purpose of the pump. Some municipalities allow discharge into a storm drain; check your local code before you connect to any public system. In winter, the discharge point should be above ground so water does not freeze in the pipe and back up into your basement. If you live in a cold climate, you may need to bury the pipe below the frost line or use an insulated discharge line.

Installing the check valve and pump

A check valve goes on the discharge pipe just above the pump outlet. This one-way valve allows water to flow out but prevents it from flowing back into the pit when the pump stops. Without a check valve, water in the discharge pipe will drain back into the basin, forcing the pump to work harder and shortening its life. Install the check valve with the arrow pointing away from the pump, toward the outside discharge point.

Set the pump in the basin on top of the gravel or sand at the bottom. The pump sits on a small platform or rests directly on the basin floor, depending on the model. Connect the discharge pipe to the pump outlet, then run the power cord to a GFCI-protected outlet — never use an unprotected outlet for a sump pump. The float switch (a small ball or cup that rises and falls with water level) should move freely inside the basin without hitting the pump or the basin walls. Test the float by pouring water into the basin slowly; the pump should turn on when the water reaches the float and turn off when it drains.

Sealing the pit and finishing the installation

Once the pump is running and the discharge pipe is in place, seal the top of the pit with the basin lid or a piece of plywood. This keeps debris, insects, and radon gas from entering the pit. If you use a lid with a hole for the discharge pipe, make sure the hole is snug around the pipe so nothing falls in. A sealed pit also prevents moisture from rising into your basement.

Check your local building code to see whether you need a permit for the sump pit installation. Some jurisdictions require an inspection before you cover the pit, and some have rules about pit depth, basin size, or discharge location. If your code requires a permit, get one before you dig — an unpermitted pit can affect your home's resale value or your homeowner's insurance claim if water damage occurs.

Maintenance to keep the pit working

A sump pit needs regular attention to stay effective. Every few months, pour a bucket of water into the pit to test the pump and float switch. If the pump does not turn on, the float may be stuck or the outlet may be blocked. Clean the intake screen (the small grate at the bottom of the pump) by removing the pump and rinsing it under running water. Sediment and debris accumulate over time and can jam the impeller.

In spring and after heavy rain, check the discharge pipe outside to make sure it is not frozen, clogged, or disconnected. If water is pooling near your foundation instead of flowing away, the pipe may have shifted or the slope may have changed. The pump itself usually lasts 5 to 10 years; if it runs constantly or makes unusual noises, it may be wearing out and need replacement.

Frequently Asked Questions

Do I need a permit to build a sump pit?

Requirements vary by city and county. Some jurisdictions require a permit and inspection before you cover the pit; others do not regulate sump pits at all. Contact your local building department or code office before you dig. An unpermitted pit may not be covered by your homeowner's insurance if water damage occurs.

What size should the sump pit be?

Most residential sump pits are 18 to 24 inches in diameter and 2 to 3 feet deep. The basin should be large enough to hold water between pump cycles so the pump does not turn on and off constantly. A larger pit is better than a smaller one if you have a lot of water entering your basement.

Can I use a regular bucket instead of a sump basin?

A plastic sump basin is better than a bucket because it has drainage holes in the floor and a lid that seals properly. A bucket will eventually rust or crack, and water cannot enter from below. A basin costs $30 to $80 and lasts much longer.

What happens if the pump loses power?

Water will continue to seep into the pit and may overflow into your basement if the power is out for a long time. A battery backup pump or a generator can keep the main pump running during an outage. If you live in an area with frequent power failures, a backup system is worth the cost.

How far away should the discharge pipe empty from my house?

At least 10 feet from your foundation is the standard rule. Water that empties closer will seep back into the soil around your basement and return to the pit, defeating the pump's purpose. In some areas, you can discharge into a storm drain or dry well instead of letting it run across your yard.