The City of Houston is preparing to ask Congress for $2 billion more to help residents whose homes were damaged by Hurricane Harvey — a request likely to coincide with lawmakers’ consideration of aid to victims of hurricanes Florence and Michael, which devastated sections of North Carolina and Florida.

The city is basing its request on a new study that departs from the traditional method of calculating need. The difference boils down to who gets counted.

The U.S. Department of Housing and Urban Development looks at recipients of individual assistance from the Federal Emergency Management Agency to determine how much additional aid is needed. Houston’s study includes many more people affected by Harvey’s flooding, whether or not they applied for aid from FEMA.

“We’re chronically undercounting the most vulnerable populations,” said Tom McCasland, director of the Houston Housing and Community Development Department. “That’s why it’s important not to start with FEMA.”

If Congress agrees to the additional appropriations, Houston’s methodology would influence how other cities calculate unmet need following disasters.

But HUD spokesman Brian Sullivan said such local analyses are common among cities and states making their case for more funding. He noted such studies tended to have “more expansive” estimates of unmet needs than HUD estimates, arguing that HUD’s standards mean communities are treated equally after disaster strikes.

“HUD has a methodology we use to try to establish a common yard stick across all disasters so Congress can make a determination if they want to fund more or less than they have in the past,” he said.

Houston based its analysis on flood modeling that uses data points such as drone imagery of the storm and flooding. The city’s Housing and Community Development Department now has maps of every lot and building in the city with blue shading representing areas that were likely submerged.

Houston’s analysis also considered factors such as the building’s size and the lot’s surface permeability to calculate the likely damage caused to the home and its contents.

The conclusion: Harvey inflicted $16 billion of residential damage on the city, $3.1 billion of which the city believes meets HUD’s criteria for unmet need. That’s about $2 billion more than the amount HUD is already sending for unmet housing needs in Houston.

Whether or not Houston receives the additional $2 billion, the study will influence policy. McCasland said neighborhoods such as Braeburn, East Houston, Golfcrest, Greater Fifth Ward, Greenspoint, Gulfton, Hunterwood, Inwood, Lawndale, Midwest, Northshire and Northside would be a focus for the incoming housing recovery funds because many residents suffered property damage that would cost more than 50 percent of their annual incomes to replace.

The data may even inform future decisions on where to build in Houston and what construction precautions, such as elevating homes, should be taken. “This is the good data that we need for data-driven policy,” McCasland said.