Install flood vents

Overview

Flood vents are small permanent openings that allow floodwater to flow freely through a crawlspace or other enclosed area below the Base Flood Elevation (BFE). Also known as flood openings, they must be installed in foundation walls (load bearing and non-load bearing) when a building has any enclosed area below the BFE. Flood vents allow water to freely enter and exit a structure to equalize the hydrostatic and hydrodynamic pressures exerted by floodwaters. If floodwaters are unable to enter a structure, the pressure exerted on the foundation walls can cause them to collapse. Flood vents allow water levels on either side of the wall to rise at the same rate – equally – and prevent the foundation from collapsing. The bottom of each opening must be no higher than one foot above the ground to allow water to enter the interior and reduce pressure on the exterior side of the walls.

It is critical to install the appropriate number and size of flood vents. If not enough openings are installed, the water pressures on the exterior walls of the building will not be equalized. In general, for every square foot of enclosed area, one square inch of opening in a foundation wall should be installed, with a minimum of two openings on different walls of the enclosed area. Requirements for the number and size of flood vents can vary based on your community’s regulations and your individual insurance requirements.

Note that if you live in an area where floodwaters are known to flow and rise quickly, such as in a Coastal A Zone or an area prone to flash flooding, flood vents might not be the best strategy for your building, as waters can rise so quickly that the openings may not be able to equalize the external pressures before the foundation walls fail. In these cases, a different technique should be considered to minimize or prevent flood damage. An analysis by a structural engineer can provide the best advice.

Flood vents can be installed in residential and commercial buildings. They are typically included in elevated structures that have enclosed areas underneath the structure. While they can include screens, louvers, or decorative coverings, flood vents must remain unobstructed to allow floodwater access. Annual inspection of all openings is recommended to make sure that they are not blocked and operate as designed. Blocked flood vents can violate a structure’s building permit.

Next Steps

1. Consult your local floodplain manager and insurance agent to make sure to install the proper number of flood vents and/or provide certified plans to show that the design meets the structure’s needs.
2. Contact a qualified contractor, knowledgeable about flood vents, to design and install the appropriate size and number of flood vents for your structure. If you plan to use engineered openings, your local floodplain manager or building official may want to see the manufacturer’s specifications for the vents before you install them.
3. Your building permit should specify the size and location of the flood openings you plan to install. Once the installation is complete, check to make sure that you have the right number installed.

Special Considerations

• This mitigation option type is only recommended in areas with low velocity flooding, where water moves at less than 3 feet per second. If you do not know the projected flood velocity around your property, check with your local floodplain manager.
• If your structure is in less than fair condition, this mitigation option type is not recommended. The only mitigation option types recommended for structures in fair to poor condition are acquisition, demolition, and the purchase of flood insurance or business interruption insurance.
• Be aware that older structures may require hazardous material abatement (e.g. asbestos, lead paint) before vents can be installed, which could add significant cost to your project.
• Ensure compliance with all applicable National Flood Insurance Program (NFIP) requirements and local building codes. The NFIP sets minimum standards and allows individual communities to adopt their own additional or more stringent requirements via local floodplain management ordinances, regulations, and laws.
• If your building sustained substantial damage during a recent flood event, you may be required to bring it into compliance with NFIP and local floodplain management regulations. Your local floodplain manager can give more information about this.
• Be careful not to redirect water flow from your property onto another property. No adverse impact (NAI) floodplain management is an approach that ensures the action of any property owner, public or private, does not adversely impact the property and rights of others. NAI calls for any adverse impact caused by a project to be mitigated as part of the project. By following NAI principles, you can: prevent flooding from increasing or damaging others; see a reduction in flood losses over time; and avoid challenges and lawsuits over causing or aggravating a flood problem.
• Create a disaster plan. Be aware of all actions you will need to take once you receive warning of an oncoming flood event — and how much time each action will take to complete. Actions could include ensuring flood vents are clear, installing flood shields, or closing barrier gates. Annually, inspect all removable pieces to make sure they are in good condition — and you have all necessary parts. Make sure whoever is identified to complete each action in your disaster plan knows how to perform the action, is physically able, and will be onsite. Once everything is in place to protect your home, you should evacuate to higher ground.
• Contact a local flood insurance representative to learn more and get a quote, if you do not already have flood insurance. (Most homeowner’s insurance policies do not cover flood damage.)
• Renters and those who own specific types of property may be limited in which mitigation options they can undertake or have different requirements to which they must adhere. If you are a renter or own any of the following listed property types, click through to learn more: Renter; Unit in a multifamily residence; Manufactured home; Farm/ranch; Historic property; New construction.