Homeowners and contractors remodeling in a flood zone

Where is the building?

Free check of whether your remodel or repair trips FEMA's 50% rule, from the building's market value and the project cost. Your floodplain office decides.

Free to read
No sign-up until the draft
Hands off to the right door

ePlan fills in

Flood zone
Base flood elevation
Parcel record

How it works

Substantial improvement check, from one answer

Enter the address, the building's value and the project cost.
ePlan reads the flood zone and works out the share. Your floodplain administrator makes the official call.
Read the free check. Adding a backyard unit instead? Start an ADU permit draft.

What you get

Substantial improvement check and 1 more document

The check is free. The paperwork after it is drafted at the ADU permit door.

The first draft

Substantial improvement check (free)

Flood zone and base flood elevation
Market value of the structure
Project cost
Cost as a share of value
What happens at 50% or more
What your floodplain administrator will ask for

Next · 2

ADU permit application

Site plan
Floor plan
Utilities

From public data

What ePlan fills in, and from where

Flood zone and base flood elevationFEMA National Flood Hazard Layer (Map Service Center)
Parcel recordRegrid nationwide parcel data
Ground elevationUSGS 3D Elevation Program

50%

of the structure's market value is the line: work costing that much or more is a substantial improvement
Source: 44 CFR 59.1, eCFR

Ready for the paperwork?

Check your lot against California ADU law: size, setbacks, fees and the 60-day review clock. Get the permit narrative and checklist; bring your drawings.

ADU permit →

Questions

FEMA 50% Rule Calculator: what people ask

What is a substantial improvement?

Any reconstruction, rehabilitation, addition or other improvement whose cost equals or exceeds 50 percent of the structure's market value before construction starts. It includes work on structures that have had substantial damage.

Source: ecfr.gov

What is substantial damage?

Damage of any origin where restoring the structure to its before-damage condition would cost 50 percent or more of its market value before the damage occurred.

Source: ecfr.gov

What happens if my project crosses 50%?

It must meet the same elevation rules as new construction. In zones A1-30, AE and AH, a substantially improved home must have its lowest floor, including the basement, at or above the base flood level.

Source: ecfr.gov