Understanding Floor Area Ratio (FAR) & Lot Coverage

The Biggest Bottleneck in Luxury Development

In San Mateo and Santa Clara counties, the value of a teardown property is not determined by its current state. It is determined by what you are legally allowed to build on it. The absolute upper limit of that potential is dictated by a single metric: Floor Area Ratio (FAR).

What is Floor Area Ratio (FAR)?

Floor Area Ratio is the relationship between the total usable floor area of a building and the total area of the lot on which the building stands.

For example, if you purchase a 10,000 square foot lot in a neighborhood with a maximum FAR of 0.40, the absolute largest home you can build is 4,000 square feet (10,000 x 0.40).

Why FAR Makes or Breaks a Teardown

If you buy an aging 2,500 square foot home on a 10,000 square foot lot, its teardown value depends entirely on the FAR.

• If the FAR is 0.25, you can only build a new 2,500 square foot home. The margin for developer profit is incredibly thin.
• If the FAR is 0.50, you can build a massive 5,000 square foot luxury estate, effectively doubling the usable space and drastically increasing the After Repair Value (ARV).

The Complexity of Peninsula Zoning

Unfortunately, determining your maximum build size is rarely as simple as checking a single FAR percentage. Local jurisdictions have developed incredibly complex "mansionization" ordinances to prevent bulky, oversized homes from dominating neighborhoods.

1. Sliding Scale FAR

In exclusive enclaves like Atherton or Hillsborough, FAR is not a fixed percentage. It operates on a sliding scale based on lot size. The larger the lot, the lower the permitted FAR percentage. This ensures that massive lots retain a park-like, open feel, but it severely limits a developer's ROI if they miscalculate the sliding scale.

2. Exemptions and Inclusions

What actually counts toward your "Total Building Square Footage"? It varies by city.

• Basements: In some cities, subterranean basements do not count toward FAR, which is why luxury spec homes in Menlo Park frequently feature massive, fully-finished lower levels.
• Covered Parking: Does the 400 square foot attached garage count toward FAR? In some jurisdictions, yes. In others, a certain allowance is exempted.
• Double-Height Ceilings: A grand, two-story foyer may look like one room, but some zoning codes count any space with ceilings over 15 feet as double square footage against your FAR limit.

3. Lot Coverage vs. FAR

Do not confuse FAR with Lot Coverage. Lot coverage simply dictates the footprint of the building on the ground. A city might allow a 35% lot coverage but a 50% FAR. This forces developers to build two-story homes to maximize their allowed square footage, rather than sprawling single-story ranchers.

Automating Zoning Intelligence

Manually checking the zoning code, daylight planes, and FAR exemptions for every property that hits the market is a recipe for missed opportunities.

AddressIntel's platform maps the complex zoning overlays of the Peninsula. When we identify a property, our algorithm automatically calculates the maximum allowable build size based on the specific local ordinances, letting you instantly spot the lots with the highest untapped FAR potential.