How Sandbags Work

Building the Sandcastle: Placing the Bags

Sandbags stacked in a pyramid formation.
Sandbags stacked in a pyramid formation.
© Lavrentev

When you think about preparing for a flood and battening down the hatches, you might envision piles and piles of the sandbags you just pulled together stacked in front of your home - the bigger the better. Wrong. You don't want your wall to be too high or it will lose effectiveness and not withstand the water. Here are the steps you may want to follow when placing sandbags:

  • Before you build at all, you'll want to clear away the area where the bags will go. Move leaves, branches and rocks away so that your sandbag barrier will be as flush with the ground as possible.
  • Next, you may want to dig out a trench approximately one bag deep by two bags wide; this step will minimize the amount of water getting under the sandbag wall.
  • After you've prepped the area, start laying bags. Your typical sandbag wall has a pyramid-type shape; it has a wide base and gets skinnier as it gets taller. This gives the wall extra support at its foundation. Lay the sandbags as you would lay bricks, each bag overlapping half of the one below it. The sand is flexible enough that it will fill in the gaps within the wall, similar to mortar in a brick wall.
  • Make sure the folded area of the bag faces upstream, or the direction from which the water will be coming.
  • You don't want the sandbag wall to be higher than two to four layers. If you stack the sandbags directly against a building, the wall can be higher.
  • Once the sandbags are laid, stomp on them to fill in any gaps and press the bags tightly together.
  • If the sandbags will be sitting out for an extended period of time, consider placing plastic sheeting over the sandbag wall to serve as additional protection.

[sources: State of California, The Resource Agency, Department of Water Resources; FEMA]

Keep in mind that you also want to use sandbags in doorways and other openings in a home.