FAR And Lot Coverage In Los Altos Hills

Thinking about adding square footage on a Los Altos Hills property, but not sure what the Town will allow? You are not alone. Between hillside constraints, design review, and technical definitions, it can be tough to know what really counts toward your limits. In this guide, you’ll learn how FAR and lot coverage work, what usually counts, where exceptions apply, and how to size a project before you hire an architect. Let’s dive in.

FAR basics

Floor Area Ratio, or FAR, compares a home’s total counted floor area to the lot size. It controls overall building bulk on the site.

• Formula: FAR = total counted floor area ÷ lot area.
• Units: expressed as a decimal or percent, like 0.10 or 10%.
• Purpose: manage scale and neighborhood character.

What usually counts toward FAR

• Conditioned living space in the primary residence.
• Enclosed areas that meet the local definition of “floor area,” which can include attached garages when they are enclosed or conditioned.
• Enclosed, finished upper levels that meet minimum height and habitability criteria.

What often does not count toward FAR

• Fully below‑grade basements that are substantially under finished grade, subject to local definitions.
• Open, unconditioned structures such as uncovered decks or open trellises.
• Small detached utility structures below a local size threshold, depending on code.

Always confirm the Town’s definitions of “floor area” and any special exemptions before you rely on them.

Lot coverage basics

Lot coverage measures how much of your site is covered by building footprints and roofed areas. It controls the ground‑level impact of structures.

• Formula: Lot coverage (%) = counted building footprint ÷ lot area × 100.
• Purpose: limit site coverage and manage stormwater and perceived massing.

What usually counts toward lot coverage

• The main house footprint.
• Attached garages and carports.
• Covered porches, roofed decks, porte‑cocheres, and most roofed accessory buildings.

What often does not count toward lot coverage

• Landscaped areas and permeable surfaces.
• Unroofed, at‑grade patios and open decks, unless local rules treat them differently.
• Certain minor structures under a height or size threshold.

Again, local definitions control exactly what is included.

How Los Altos Hills applies these limits

Los Altos Hills has a semi‑rural, hillside setting. Many properties face more than just numerical FAR and lot coverage limits. Your buildable area can also be shaped by:

• Hillside and slope rules that restrict grading and development on steeper terrain.
• Tree protection that can limit siting and require mitigation.
• Design review processes for exterior massing changes.
• Utilities and fire access standards, plus septic capacity on larger lots.
• Setbacks, height limits, creek or conservation setbacks, and easements.

In practice, the tightest constraint wins. Even if FAR suggests you can build more, slope, setbacks, or height can reduce what fits.

What counts in LAH, item by item

The Town’s municipal code defines what counts. These are common California practices you can use as a starting point while you verify specifics with Town staff:

• Primary residence. Counted in FAR and lot coverage.
• Attached garages. Often counted in lot coverage. FAR status depends on whether the space is enclosed and conditioned, and on the Town’s definition of floor area.
• Basements. Fully below‑grade basements are often excluded from FAR. Partially above‑grade basements typically count. Lot coverage is unaffected unless the basement extends beyond the footprint.
• Attics and mezzanines. Usually count toward FAR only if they meet minimum height and habitability criteria.
• Covered but open structures. Unconditioned, open porches often do not count toward FAR, but roofed porches and decks usually count toward lot coverage.
• Accessory dwelling units. ADU treatment under FAR and coverage varies by city because state ADU laws limit local restrictions. Confirm current Town policy.
• Detached accessory buildings. Small sheds or similar structures may be exempt below a size threshold. Verify the Town’s cutoff and whether coverage still applies.
• Carports and porte‑cocheres. Typically counted toward lot coverage because they are roofed.
• Below‑grade parking. May be excluded from FAR if substantially below grade. The roof slab can still count as lot coverage unless treated as landscape under local rules.
• Eaves and overhangs. Many codes exempt eaves up to a set width from coverage. Check the Town’s threshold.

Planning constraints that matter most

On 1 to 2 plus acre parcels, these additional limits can drive your design:

• Slope and grading limits that restrict cut and fill.
• Tree surveys and preservation plans that influence siting and costs.
• Height limits that reduce second‑story massing.
• Septic capacity and fire access that can shift where you build and how much.

Treat FAR and coverage as part of a bigger envelope that also includes setbacks, slopes, height, and environmental buffers.

Simple examples, clearly labeled hypothetical

These examples use hypothetical FAR and lot coverage numbers. Replace with the Town’s current standards for your zoning district after you verify them.

Example A — 1 acre (hypothetical 10% FAR and 10% coverage)

• Lot area: 43,560 sq ft.
• FAR allowance: 0.10 × 43,560 = 4,356 sq ft of countable floor area.
• Lot coverage allowance: 10% × 43,560 = 4,356 sq ft of footprint.
• If your home has 2,500 sq ft of counted living area and a 900 sq ft counted garage, you have 3,400 sq ft counted. Remaining FAR: 4,356 − 3,400 = 956 sq ft.
• If your footprint totals 2,700 sq ft, remaining coverage: 4,356 − 2,700 = 1,656 sq ft.

Example B — 2 acres (hypothetical 10% FAR and 10% coverage)

• Lot area: 87,120 sq ft.
• FAR allowance: 0.10 × 87,120 = 8,712 sq ft.
• Coverage allowance: 8,712 sq ft.
• On larger hillside parcels, practical buildable area is often limited more by slope, setbacks, tree preservation, and septic than by the raw FAR or coverage math.

Step‑by‑step to size your project

Use this workflow to estimate what is feasible before you pay for full design work:

1. Obtain parcel data

• Lot area in square feet, the APN, and your legal description. Pull from official parcel records.

2. Confirm zoning and basic limits

• Identify your zoning district, then note FAR, maximum lot coverage, setbacks, height, minimum lot size, and accessory structure rules.

3. Gather existing conditions and permits

• Find as‑built plans if available, prior approvals, and current counted floor area and impervious coverage.

4. Order surveys

• Commission boundary and topographic surveys that show contours, trees, watercourses, and existing structures.

5. Calculate current FAR and coverage

• FAR = counted floor area ÷ lot area. Coverage (%) = counted roofed footprint ÷ lot area × 100. Use the Town’s definitions to decide what to include.

6. Identify constraints and exemptions

• Note any local exceptions that may help, such as below‑grade areas or small detached structures that might be excluded.

7. Request a pre‑application consult

• Ask Planning staff to confirm interpretations and flag design review triggers or technical studies you will need.

8. Test fit options

• Have an architect prepare schematic massing that fits within the likely envelope, with rough costs and permitting timelines.

9. Plan for technical reports

• Expect geotechnical, arborist, hydrology, and fire access input on hillside or complex sites.

Common pitfalls to avoid

• Assuming all basements are free. Partially above‑grade basements often count toward FAR.
• Forgetting coverage while chasing FAR. You can hit the footprint limit on single‑story layouts even if FAR remains.
• Overlooking slopes or creek setbacks. These can shift your buildable area more than FAR or coverage.
• Miscounting garages and porches. Enclosed garages may count toward FAR, and most roofed porches count toward coverage.
• Ignoring eave and small‑structure rules. These small details can change coverage totals.

Permits and timelines

• Ministerial permits. Smaller, code‑conforming additions that stay within objective standards can sometimes move through a simpler process.
• Discretionary review. Exterior massing changes, hillside grading, protected trees, or any request for exceptions can trigger design review and public noticing with longer timelines.
• Technical studies. On hillside parcels, geotechnical and arborist reports are common prerequisites before plan approvals.

How an expert advisor helps

If you are buying or considering a significant addition or new build, the smartest first step is to align the numbers with the site. That means confirming FAR, coverage, and setbacks, then overlaying slope, trees, septic, and fire access. A construction‑informed real estate advisor can help you spot constraints early, frame realistic scope and budget, and avoid redesigns later.

Ready to size your options and plan a clear path forward? Connect with David Bergman for local, construction‑savvy guidance on Los Altos Hills properties.

FAQs

What is FAR in simple terms for Los Altos Hills?

• FAR compares your counted floor area to your lot size. It limits overall building bulk and works alongside setbacks, height, and slope rules.

What is lot coverage and why does it matter?

• Lot coverage measures the roofed footprint on the ground. It controls site coverage and can limit single‑story expansions even if FAR remains.

Do basements count toward FAR in Los Altos Hills?

• Fully below‑grade basements are often excluded, while partially above‑grade basements typically count. Confirm the Town’s definition before you design.

Do attached garages count toward FAR and coverage?

• Attached garages usually count toward lot coverage. Whether they count toward FAR depends on how the Town defines floor area and whether the space is enclosed or conditioned.

Do ADUs count toward FAR or lot coverage?

• State ADU rules shape how cities count ADUs. The treatment varies by jurisdiction, so verify the Town’s current policy for FAR and coverage.

Which typically limits projects more, FAR or coverage?

• It depends on your design and site. Single‑story plans often hit lot coverage first, while two‑story massing can be limited by FAR, height, or slope rules.

How should I start evaluating my buildable area?

• Confirm zoning limits, pull surveys, calculate current FAR and coverage using the Town’s definitions, and request a pre‑application meeting with Planning to validate your assumptions.