Understanding Floor Area Ratio (FAR) & Lot Coverage
A developer's guide to navigating Floor Area Ratio (FAR) limits, daylight planes, and zoning restrictions in San Mateo County.
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.
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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.
Frequently Asked Questions
What is Floor Area Ratio (FAR)?
FAR is the relationship between the total usable floor area of a building and the total area of the lot it sits on: FAR = Total Building Square Footage / Total Lot Square Footage. On a 10,000 square foot lot with a maximum FAR of 0.40, the largest home you can build is 4,000 square feet.
Why does FAR make or break a Peninsula teardown?
A teardown’s value is set by what you can legally build, not by the existing structure. On a 10,000 square foot lot, a 0.25 FAR caps you at a 2,500 square foot home and razor-thin margins, while a 0.50 FAR lets you build a 5,000 square foot estate — roughly doubling the usable space and the After Repair Value.
What is sliding scale FAR?
In exclusive enclaves like Atherton and Hillsborough, FAR is not a fixed percentage — it scales down as lot size goes up. The larger the lot, the lower the permitted FAR percentage, which keeps big lots feeling park-like but can severely cut a developer’s ROI if the sliding scale is miscalculated.
Do basements, garages, and tall ceilings count toward FAR?
It varies by city. Subterranean basements are exempt in some jurisdictions, which is why Menlo Park spec homes often have huge finished lower levels. Attached garages count toward FAR in some cities and are partly exempt in others, and a double-height space over 15 feet can be counted as double square footage against your limit.
What is the difference between FAR and lot coverage?
Lot coverage dictates the building’s footprint on the ground, while FAR governs total floor area across all stories. A city might allow 35% lot coverage but 50% FAR, which forces developers to build two-story homes to capture their full allowed square footage rather than sprawling single-story ranchers.
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