Planning a remodel, second story, or new build in Los Altos? Before you sketch a single line, you need to understand how the city’s floor area ratio and lot coverage rules shape what is possible on your lot. It can feel technical at first, especially if you are comparing options like a bigger first floor versus a partial second story. With a few plain‑English definitions and a simple process, you can estimate your capacity and avoid costly redesigns later. Let’s dive in.
What FAR means
Floor area ratio, or FAR, is the relationship between a home’s total gross floor area and the size of the lot. In simple terms, FAR sets the ceiling on how much interior square footage you can build. It is expressed as a decimal. For example, an FAR of 0.5 means your total allowable floor area equals 50 percent of your lot area.
What counts as “floor area” is defined by the Los Altos Municipal Code. Some spaces may count fully, count partially, or be exempt. That can include finished basements, enclosed garages, attics, and covered porches. Always confirm the exact definition with Planning so your calculations match how the city measures area.
Why FAR matters: it drives the total potential size of your project. If you are buying for value‑add potential or weighing a major expansion, FAR tells you the theoretical maximum square footage you can pursue, subject to other rules.
What lot coverage means
Lot coverage is the percentage of your lot that is covered by the building footprint at ground level. Think of it as the area under the roof, measured on a plan view. Coverage limits help protect open space and stormwater performance and keep yards usable.
Coverage is not the same as FAR. FAR looks at all levels stacked, while coverage is only the ground‑level footprint. A two‑story home can keep coverage lower by building up instead of out. If coverage is tight on your lot, you may need a second story to reach your allowed floor area.
Setbacks and the buildable envelope
Setbacks are minimum distances from your property lines where you cannot build. Los Altos sets standards for front, side, and rear setbacks. These rules carve a buildable envelope inside your lot. Even when FAR suggests you have room, setbacks can limit where you place that space.
Other envelope controls matter too. Height limits cap how tall you can build and may affect whether a two‑story design is feasible. Upper‑story step‑backs, side articulation, and design compatibility standards can also influence massing. On some parcels, special overlays, slope rules, tree protection, or historic context can further reduce where and how you build.
How rules affect projects
Small remodel or second story
If you plan a small interior remodel, these rules may have minimal impact. Once you add exterior area or a second story, lot coverage and setbacks become critical. You might be able to add a partial second story over a conforming footprint, but height limits and step‑backs can require you to pull that second story inward from the first floor below.
If your existing home is nonconforming, meaning it was built under older rules and does not meet today’s setbacks or coverage, expansion can be limited. Many cities allow you to keep a legal nonconforming structure, but enlarging the nonconforming portion is often restricted without a variance. Confirm with Planning how Los Altos treats your specific case.
Larger addition or full second story
For a larger addition, start with the FAR math to confirm there is enough room on paper. Then test coverage and setbacks. It is common to discover that a theoretical FAR surplus cannot be fully realized because the footprint cannot grow due to setbacks or trees. An architect familiar with Los Altos rules can help resolve this with alternative layouts or a partial second story that respects the envelope.
New build or teardown
If you are rebuilding, you have the chance to shape a new design to fit all limits from the start. FAR gives you the total size target, and coverage plus setbacks determine the footprint. Height and design standards guide how to distribute that area across floors. Even when a plan is technically compliant, neighborhood compatibility review can lead to design refinements that reduce perceived mass and improve fit.
ADUs and accessory structures
Accessory dwelling units are influenced by state law and local rules. Some cities exempt ADU floor area from FAR or lot coverage, while others count it fully or partially. Maximum ADU size, setbacks, and parking are often shaped by state mandates. Because ADU policy has evolved rapidly in recent years, confirm with Los Altos Planning how ADUs are counted toward FAR and coverage today and what standards apply to your lot.
Detached garages, carports, and other accessory buildings may be measured differently. Open structures or small sheds can have separate treatment. Ask Planning how each space will be counted so you can prioritize features without unexpected impacts on coverage or FAR.
Quick math to estimate
Use this simple process to gauge what might be possible on your parcel:
Find your lot area. Use county records or a city parcel viewer to get the square footage.
Confirm your zoning and FAR. Look up your zoning district on the city zoning map and find the applicable FAR in the Municipal Code or a planning standards table.
Calculate maximum floor area. Multiply lot area by FAR to get your maximum gross floor area.
Determine what is counted. Using city definitions, total up your existing counted area. Clarify how basements, garages, attics, and porches are treated.
Estimate remaining capacity. Subtract counted existing area from the maximum to find your theoretical remaining square footage.
Check lot coverage and setbacks. Multiply lot area by the allowed coverage percentage to find the maximum footprint, then test whether your planned footprint fits within setbacks.
Confirm height and stories. If coverage is tight, you may need to build up. Make sure height limits and any step‑back standards allow your second‑story plan.
Account for site features. Tree protection, easements, and required open space can reduce the usable envelope.
Example A: small lot (hypothetical)
- Lot size: 5,000 sq ft. FAR: 0.4. Maximum floor area: 2,000 sq ft.
- Existing house: 1,600 sq ft counted. Remaining theoretical capacity: 400 sq ft.
- If you want a 600 sq ft addition, you would need to redesign to reduce counted area or seek discretionary relief. Coverage and setbacks could further limit footprint growth.
Example B: larger lot with ADU (hypothetical)
- Lot size: 8,000 sq ft. FAR: 0.5. Maximum floor area: 4,000 sq ft.
- Existing main house: 3,200 sq ft. Proposed ADU: 800 sq ft.
- If Los Altos exempts ADUs from FAR, the ADU might not use up your main‑house allowance. If ADUs count toward FAR, your combined total hits the 4,000 sq ft limit. Confirm current ADU policy with Planning before you commit to a layout.
Planning steps in Los Altos
Start with a pre‑application check. Confirm zoning, lot area, and any overlays. Ask Planning for the definitions of floor area and lot coverage and how they measure height. If your site has protected trees, note their locations and root zones.
Assemble the right team. An architect who works in Los Altos can design to the city’s envelope rules and prepare submittal‑ready plans. If you anticipate a tight interpretation issue or a variance, consider a permit expeditor or planning consultant. A surveyor can verify lot lines and setbacks when every foot matters.
Prepare your submittal. Most projects need a site plan, floor plans, elevations, and sometimes shadow studies or tree protection plans. Ask whether your project is ministerial or discretionary. Ministerial projects are reviewed for code compliance without public hearings. Discretionary projects may require public notice and hearings and can take longer.
Coordinate reviews. Where allowed, submit planning and building packages concurrently to streamline the schedule. Budget time for back‑and‑forth comments, and plan neighbor outreach early for larger additions or new builds.
Risks and red flags
- Over‑relying on theoretical FAR without testing setbacks, height, and coverage can overstate what you can build.
- Nonconforming homes often cannot expand in ways that increase the nonconformity. This can constrain additions along a tight side yard or front setback.
- Protected trees and landscape requirements can reduce placement options and add mitigation costs.
- Overlay districts, hillside rules, or historic contexts can add stricter standards beyond base zoning.
- ADU policy and state law continue to evolve. Always confirm how Los Altos applies current rules to FAR and coverage.
Pre‑draw checklist
- Verify your lot area, zoning district, and any overlays.
- Confirm FAR, lot coverage, setbacks, and height limits in the Municipal Code or a city standards table.
- Clarify what counts as floor area for basements, garages, attics, and porches.
- Ask Planning whether ADU floor area is exempt from FAR or coverage and what size standards apply.
- Identify protected trees, easements, and site constraints early.
- Schedule a pre‑application meeting to confirm interpretations.
- Engage a Los Altos‑savvy architect and, if needed, a surveyor or arborist.
When to call experts
Bring in an architect as soon as you have a basic program and budget. Ask for quick test fits that honor setbacks, coverage, and height. If you are buying a property with value‑add potential, a rapid planning check before you remove contingencies can protect your assumptions. For tight or unusual sites, add a surveyor and arborist to the team. If you anticipate a variance, consult a planning professional about findings, notice requirements, and timelines.
If you want a second opinion on feasibility, costs, and how these rules affect resale value, you can lean on a team that blends brokerage and construction experience. That combination helps you decide whether to renovate, rebuild, or sell as‑is with a clear view of what the site can support.
Ready to evaluate your Los Altos property through the lens of FAR, coverage, and setbacks, or want help pressure‑testing a purchase? Reach out to the Moussavian Real Estate Team for a practical, data‑driven plan for your next step.
FAQs
What is FAR in Los Altos residential zoning?
- FAR is the ratio of total gross floor area to lot area, which sets the maximum interior square footage allowed on a parcel, subject to other standards.
What counts toward FAR in Los Altos?
- It depends on the city’s definitions for floor area; confirm how garages, basements, attics, and covered porches are counted before finalizing plans.
How is lot coverage different from FAR?
- Lot coverage limits the ground‑level footprint under the roof, while FAR counts stacked area across all levels, so a two‑story home can reduce coverage but still meet FAR.
Do garages and basements count in Los Altos?
- Many cities count enclosed garages and certain basements, but rules vary by jurisdiction, so verify Los Altos’ definitions with Planning.
Can I add on if my home is nonconforming?
- Nonconforming structures often can remain, but expansions that increase nonconformity are commonly restricted or require a variance that is not guaranteed.
Are ADUs exempt from FAR and coverage?
- ADU treatment varies and has been shaped by state law; ask Los Altos Planning whether ADUs are exempt, partially counted, or fully counted toward FAR and coverage.
How long does permitting take in Los Altos?
- Timelines depend on scope and whether your project is ministerial or discretionary, with simple permits taking weeks to months and larger reviews taking several months or more.
How do I find my zoning and limits?
- Check the city zoning map for your district, then review the Municipal Code and any residential standards tables or speak with Planning for parcel‑specific answers.
