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Stormwater BMPs for Citizens





Sandbag Use Guidelines

How do I use sandbags?

Sandbags alone should not be relied on to keep water outside a building. Use baffle boards (plywood sheeting) or sheets of plastic tarp with sandbags. To form a sandbag wall, place bags tightly against one another to form the first layer of defense. Stagger the second and subsequent layers of bags, much like the pattern of bricks in a wall.

Sandbags should never be used to build a fortress around the perimeter of one's property. Doing so can actually trap floodwaters between sandbag walls and
structures, leading to further damage.

Steps to protect your home

How to make baffle boards to temporarily seal foundation vents, windows, doorways and garage doorways:

These steps should only be taken immediately prior to flooding and removed immediately after the threat of flooding has passed.
  • Use 3/4" plywood to overlap the window or vent by three or four inches on all sides.
  • Use a soft gasket material like felt or foam rubber that is at least 2 inches wide. Attach it with waterproof glue to the 3/4" plywood.
  • Use four or more nails, screws or bolts to secure the baffle boards over the opening. In stucco, cement or brick walls, special screws or expansion bolts will be required.
  • For doorways, install baffle boards to the outside frame of the door.
  • For garage doors, suitable boards one-inch thick may be used instead of plywood for the door seals. The bottom edge of the baffle board should be shaped to fit the driveway surface so there will be a watertight seal on the bottom. Use baffles to seal door cracks vertical to and higher than the bottom seal.
  • In an emergency, fasten sheets of plastic or building (tar) paper over the opening and seal with caulk, putty or clay.
  • Baffle boards (above), consist of 3/4 inch plywood sheets with a soft gasket material like felt or foam rubber. They are effective for closing off vents, low windows and doors from floodwater. If placed over vents, however, baffle boards must be removed once the danger of flooding passes.
  • Using plastic tarp between a structure and sandbags helps keep floodwater from seeping between the house siding and foundation sills.
  • Care should be taken to place sandbags tightly against one another. Place the next sandbag over the folded, tied end to provide a good seal. Complete each layer before starting the next layer. Limit placement to two layers.
  • After placing the first layer of sandbags, stagger the second layer of bags, much like the pattern of bricks in a wall.
Taking these precautions will minimize the amount of water and sediment entering your home and crawl space and prevent damage to your home’s structure.


Keep in mind that sealing off foundation vents prohibits air circulation under your home. Building a last line of defense around your home. These measures to protect your home should be temporary and should be removed immediately after the threat of flooding has passed. Opening vents after or in between storms is critical to protect your homes foundation and sub floor and prevent the growth of mold and mildew in your crawl space.

Before flooding is a threat

If you believe your home is in danger of being flooded, there are steps you can take in advance of a flood to reduce property damage.

For homes with cement slab floors:

  • Use special paints to keep the water from penetrating exterior stucco or brick.
  • Patch all cracks in the outside foundation with regular patching mixes.
  • Clear dirt away from the bottom of stucco or wood walls and seal the lower exposed edge with caulking compound. Replace the dirt, which will not affect the seal.
For homes with wood floors and crawl spaces:
  • Water can leak into crawl spaces and/or basements through foundation cracks, pipe holes, vents, doors or windows. It can also seep between the house siding and foundation sills. Once the crawl space or basement is filled, the water pushes up into the building through floors and wall joints until it reaches the height of the outside flood waters.
  • Seal vents and windows with plywood. Vents are required by building codes to prevent mildew and rot. Therefore, all plywood over vents must be removed as soon as the danger of a flood passes.
  • Fill cracks in the foundation or stucco wall with cement or other effective crack-filler material.
  • Seal small openings around pipes with cement, crack filler or caulk.
  • Seal the joint between siding and foundation with caulk.

When the rainy season is over

The City of Redwood City recommends that residents and business owners keep sandbags on hand at least through mid-April since significant amounts of rain can occur during late-winter and early-spring storms. Once the threat of flooding is over, however, there are several ways to dispose of sandbags.

The City filled all sandbags with clean, high quality, washed sand.

Recycle Uses For Used Sand

We can suggest the following uses for your used sand:

  •  Add or use as a soil amendment to gardens.

    • The sand is also suitable for use as cat litter. Low or high-grade sand for cat litter will work. Just add a little baking soda or litter freshener to the sand to deodorize.

  • Return used sandbags to the nearest distribution site: 1400 Broadway, the Public Works Division Parking Lot by May 1, 2004. Please place your used sandbags on the pallets in the designated area.

  • Sandbags should not be tossed into garbage receptacles because they take up valuable space in landfills.

Thanks for properly recycling your used sandbags.

This Information was Reprinted, courtesy of the Santa Clara Valley Water District. (SCVWD)

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