A buyer sees two Los Altos Hills listings on the same street. Both are described as one-acre parcels. One is priced meaningfully higher than the other, and the listing photos do not obviously explain the gap. The instinct is to blame the view, the trees, or the finish level of whatever cottage happens to be sitting on the dirt. That is usually wrong. The gap is almost always the buildable envelope, and the buildable envelope is set by a formula written into the Town's Municipal Code.
The thesis is simple: in Los Altos Hills, buyers are not paying for acreage. They are paying for permitted square footage. Once you learn to read a parcel that way, most of the pricing anomalies in the market resolve.
The mechanism most buyers miss
Los Altos Hills requires a net minimum lot size of 43,560 square feet, and the Town then translates each parcel into a Lot Unit Factor, or LUF, based on net area and average slope. The LUF is not a rounding exercise. It is the multiplier that determines everything else.
The Town's slope math, from the current worksheets and Article 5 of the Municipal Code, works like this:
| Average slope (S) | Lot Unit Factor | Maximum Floor Area | Maximum Development Area |
|---|---|---|---|
| S ≤ 10% | LUF = net acres | LUF × 6,000 sq ft | LUF × 15,000 sq ft |
| 10% < S < 30% | LUF = An × [1 − 0.02143(S−10)] | Per-LUF factor steps down linearly | LUF × [15,000 − 375(S−10)] sq ft |
| S ≥ 30% (very steep) | Reduced LUF | Floors apply | LUF × 7,500 sq ft |
Floor Area is the number that matters to the family sketching a house on a napkin. Development Area governs everything else that hits the ground: driveways, patios, pool decks, tennis courts, walkways. Both are capped, and both compress as slope increases. A steep one-acre parcel and a flat one-acre parcel are not comparable products.
There are floors on the formula. The allowable floor area on a parcel shall not be reduced to less than 5,000 square feet, except in the case of parcels which have a Lot Unit Factor of 0.50 or less, which require a Conditional Development Permit. Once a parcel's LUF drops below 0.50, the buyer is not looking at a standard build. They are looking at a discretionary review, a smaller permitted house, and a longer entitlement timeline. That is the first transaction-specific friction most out-of-market buyers do not price in.
The math that changes how you read comps
Instead of price per acre or price per square foot of existing structure, the more honest yardstick in Los Altos Hills is price per permitted square foot. Divide the asking price by the parcel's MFA. Suddenly comps that looked scattered snap into a range.
Consider two nominal one-acre parcels. Parcel A is essentially flat, an S near 5%, with an LUF close to 1.0. Its MFA lands near 6,000 square feet. Parcel B has an average slope closer to 20%. Its LUF is materially below 1.0, and its MFA compresses accordingly, often into the 4,500 to 5,000 square foot range once the linear slope penalty runs through the formula. At an identical asking price, the buyer of Parcel B is paying a meaningfully higher price per permitted square foot for a smaller house they cannot legally exceed without a variance.
This is the number to run before writing an offer. If a buyer's program is a 5,800 square foot primary residence with a pool cabana and a sport court, Parcel B is not the same product as Parcel A even if the MLS says they are both "1.02 acres."
Where value hides: basements, easements, and the flat building circle
Two provisions inside the code are quietly worth six or seven figures on the right parcel.
The basement exemption. The Town defines a basement as a floor level where the finished floor elevation of the building level above the basement is not greater than 28 inches above the adjoining natural or finished grade, whichever is lower, and at least 75% of the basement's perimeter length shall be wholly underground. Basement area is exempted from floor area. On a flat parcel with a capable geotech profile, a well-designed basement can add 2,000 or more square feet of livable program without touching MFA. That is why so many recent Los Altos Hills builds put media rooms, wine storage, guest suites, and gyms below grade. It is not aesthetic preference. It is the code.
Conservation easement recalculation. For parcels with mixed terrain, the code allows a recalculation of LUF and MFA off the gentler portion of the site when steeper areas are placed under a conservation easement. In practical terms, a buyer holding a parcel that is half flat pad and half hillside can sometimes recover permitted square footage by permanently restricting the part they were never going to build on anyway. That is a due-diligence conversation with a planner, not a listing-agent conversation.
The flat building circle. When you overlay slope, setbacks, ridgeline protections, and creek buffers, what remains is a usable pad. Two parcels with identical MFA can still differ in how the permitted square footage can actually be arranged on the ground. A long, narrow building envelope forces a different floor plan than a broad, square one. Buyers who tour with an architect see this immediately. Buyers who tour alone do not.
Substandard lots and the 0.18 rule
Not every lot in Los Altos Hills is a full acre. Legal non-conforming parcels created before current zoning are common, and they behave differently. Under the current ordinance, for substandard lots with a net area less than 1.00 acre, a Floor Area Ratio Limit of 0.18 applies, and the maximum floor area is calculated by multiplying the net lot area by a factor of 0.18. On a 30,000 square foot substandard parcel, that is a hard cap of 5,400 square feet regardless of what the LUF math would otherwise suggest. If a buyer's program does not fit inside 0.18, the parcel is the wrong parcel.
Fire hazard classification is now a line item
Cal Fire and local map adoptions have shifted portions of Los Altos Hills into Very High Fire Hazard Severity Zones. For a buyer, that classification carries real cost implications: defensible-space maintenance, ignition-resistant materials on rebuilds and additions, access and egress standards, interior sprinkler requirements on many projects, and insurance underwriting that has tightened across the Peninsula. The Town publishes the current hazard map, and it is worth pulling the parcel's classification before removing contingencies. Two adjacent lots can sit on different sides of a designation line.
What to ask for before you write the offer
The Town of Los Altos Hills maintains fillable MFA, MDA, and Parcel Water Budget worksheets, and completed worksheets for many parcels are available for review at Town Hall. A seller who has already run the numbers is doing the buyer a favor. A seller who has not is leaving the interpretation to the buyer's team.
Three requests belong in every Los Altos Hills due-diligence packet:
- The parcel's current LUF, MFA, and MDA on the Town worksheet, with the average slope calculation shown.
- The parcel's current Fire Hazard Severity Zone designation from the Town's map.
- Any prior planning correspondence flagging site-specific constraints, ridgeline visibility, or creek setbacks that would tighten the envelope below the code maximum. The Municipal Code is explicit that the standards for maximum development area are maximum standards, and the City Council and Planning Commission have the discretion to apply stricter standards to reduce development area where site specific constraints dictate further limitations.
The MFA on a worksheet is a ceiling, not a promise. That distinction is where inexperienced buyers get surprised at design review.
FAQ
If a lot's LUF is 0.50 or less, is it un-buildable? No. It is buildable, but it requires a Conditional Development Permit, and the allowable floor area may be restricted below the 5,000 square foot minimum. Maximum floor area for lots that require a Conditional Development Permit is established as the ratio of the LUF divided by 0.50, multiplied by 5,000 square feet, and the Site Development Authority may approve floor area of up to 2,500 square feet for any lot without a variance, so long as the findings for a Conditional Development Permit are made. The parcel simply moves into a discretionary lane with a different timeline and different design constraints.
Do driveways count against the development area? Partially. The first 100 feet of driveway closest to the primary dwelling, measured from the face of the garage down the centerline, is treated one way, and the portion beyond that or exceeding 14 feet in width is treated differently. On long-driveway hillside parcels, this is not a rounding error. It can consume meaningful MDA before the pool is drawn.
Is the "one-acre minimum" ever waived? The one-acre net minimum for new parcels is durable, and it is one of the founding principles of the Town's incorporation in 1956. Existing substandard lots remain legal, but they are governed by the 0.18 FAR rule described above rather than the standard LUF formula.
Working the parcel, not the price tag
The Los Altos Hills market rewards buyers who read the code before they read the comps. Median prices and price-per-acre summaries are commodity data. They travel across every portal and every neighborhood report. What they cannot tell you is whether a specific parcel will hold the house you want to build, on the pad you want to build it, at a timeline your family can absorb.
That is the work. If you are evaluating a Los Altos Hills purchase, or preparing a Los Altos Hills property for sale and want the listing to speak to buyers in the terms they actually underwrite, Ryan Gowdy can walk the parcel with you, pull the Town worksheets, and translate the envelope into a realistic program before an offer is written. Request a complimentary home valuation and consultation.
