How to find a lot’s hidden development potential

A lot’s development potential is the gap between what stands on it today and what the zoning allows. Work out the largest building the rules allow, subtract what is already there, then check which way the room can be used: an addition, a second unit, a rebuild or a lot split.

Updated October 14, 2026. General information, not legal advice: the city’s code and its planning staff decide for your lot.

Start with the gap

The largest building a district allows is the smallest of what the setbacks, lot coverage, floor-area ratio and height leave (see Lot coverage and floor-area ratio). Compare it with the footprint and the floor area that stand today. A small, old house on a large lot can leave more room than the house itself.

Four ways to use the room

• Adding on: an addition or a second story, within the setbacks and the height limit. Usually cheaper than rebuilding where the house is sound.
• A second unit: an ADU, where state law or the city allows one. See Can I build an ADU?
• Rebuilding: a new house to the full allowance, when the existing one is worth little against the land.
• Splitting the lot: two lots, where both meet the district’s minimum lot size, width and frontage. Some cities have lowered their minimum lot sizes in recent years, so read the current code.

Land value against building value

The county appraisal record splits the assessed value into the land and the improvements (the buildings). When the building is worth little against the land, investors look at the lot for a rebuild or a large addition rather than a renovation; such a house is often called a teardown. Assessed values lag the market and follow each county’s method, so read the ratio as a pointer, not a price.

What can stand in the way

• A nonconforming building: one that no longer meets today’s rules may stay, but enlarging or rebuilding it can be limited.
• Easements, building lines on the plat and deed restrictions, which the zoning map does not show.
• HOA rules, which can forbid a second unit or a second story.
• Historic and conservation districts, where demolition and new facades need approval.
• Protected trees in cities that protect them, utility lines, slope and drainage.
• Flood zones, where new floors must sit above the base flood elevation.

Flipping: where the zoning comes in

For a fix-and-flip the condition of the house and the comparable sales matter most, but the zoning still sets the ceiling. An added bedroom or bath can change what the house sells for, if the rules leave room for it, and a buyer’s lender or inspector will notice work done without a permit. Price each option against comparable sales from a local agent: the zoning tells you what is allowed, not what is worth doing.

How the Lot Report shows it

The Lot Report computes the largest building the rules allow for one US address, the footprint and floor area still free, and whether a second unit and a lot split look possible under the district’s rules, or “not determined” where the data is missing. It shows the land and building values from the county record with their ratio. Its last section plays adding on, a second unit, rebuilding and splitting the lot through with the report’s numbers; it describes and calculates, and recommends none of them.