What does it mean when a property is located in a 20-year flood plain?
Why are insurance options often limited or more expensive for homes in this zone?
Flood risk zones can be confusing—especially when lesser-known labels like the “20-year flood plain” come into play. This article explains exactly what a 20-year flood plain is, how it compares to more familiar zones like the 100- and 500-year flood plains, and why it has such a significant impact on flood insurance eligibility and cost.
The definition and annual risk of a 20-year flood plain
How it compares to 100- and 500-year zones
Why private insurers view it as high-risk
What options exist for homeowners in these areas
A 20-year flood plain (also known as a 20-year flood zone) refers to an area with a 5% chance of flooding in any given year. In statistical terms, this is a 1-in-20 annual flood probability.
This means the area could flood in any given year—five times more likely than the commonly referenced 100-year zone.
To compare:
20-year flood plain: 5% annual chance (1-in-20)
100-year flood plain: 1% annual chance (1-in-100)
500-year flood plain: 0.2% annual chance (1-in-500)
These names are probabilistic, not predictive. A "100-year flood" doesn’t mean flooding will only occur once every century—it simply means there’s a 1% chance each year.
The National Flood Insurance Program (NFIP) primarily manages zones like the 100-year flood plain, known officially as Special Flood Hazard Areas (SFHAs). However, private flood insurers often rely on different data and models to assess risk.
As a result:
Many private insurers decline to offer coverage in these areas.
Others may provide coverage but with higher premiums, coverage restrictions, or required mitigation.
Underwriting standards vary—what one insurer declines, another may accept.
A property in a 20-year zone is typically considered too risky by many private carriers, even when NFIP coverage is available.
While it’s not always possible, there are a few strategies that can help reduce flood risk or even lead to a change in zone designation:
Homeowners can submit a:
These processes require elevation certificates or surveys to demonstrate that the property is incorrectly mapped.
Actions such as:
Elevating the structure
Installing flood vents
Floodproofing basements
These may reduce premiums or increase the likelihood of coverage from private insurers.
Private flood insurers have different guidelines. One may decline coverage, while another offers a policy with acceptable terms. It often takes working with someone who understands both the NFIP and private markets to find available options.
If a property is flagged as being in a 20-year flood zone and private insurance is denied, here are a few practical next steps:
Obtain an official flood map and elevation certificate to confirm current designation
Determine if a LOMA or LOMR may be appropriate
Compare multiple insurers to identify any with more flexible underwriting
Explore flood mitigation efforts that could reduce both risk and insurance costs
Work with professionals familiar with flood zones, mitigation, and insurance navigation
A 20-year flood plain carries a significantly higher flood risk than many people realize. With a 5% chance of flooding each year, this designation can trigger higher insurance costs—or outright denial—from private carriers.
However, it doesn't always mean coverage is impossible. Risk varies by insurer, and strategies like flood mitigation or zone map revisions may open new options. Even in high-risk areas, multiple paths exist to protect property and manage insurance costs.