City Council

How to Build an ADU in Los Altos 2020 – updated

Prefab ADU as shown on Abodu website Feb 2020
Feb. 27 is ADU info nite. Panelists include custom design and prefab ADU specialists. Shown is Abodu prefab. What we know so far.
Written by lalahpolitico

UPDATE: The start time and location of the ADU info event have been changed to 6:15 pm at the Los Altos Youth Center.  [1 N. San Antonio, Los Altos]. The date Feb. 27 is unchanged.

In the fall of 2019, several State of California Housing bills were passed that further liberalized Accessory Dwelling Unit regulations. It has taken a while for cities, ADU builders, lenders and homeowners to digest them and retool. It’s easier to build an ADU in Los Altos.


Under the 2018 City of Los Altos ADU ordinance, many homeowners who wanted to build an ADU in Los Altos were prevented by the city’s lot coverage limits.  Essentially if you had already built out your primary dwelling to the near the maximum allowable lot coverage, you could not add an ADU of any desirable square footage.

But now,

2019 laws prohibit lot coverage rules that prevent an ADU of up to 850 square feet or 1000 square feet if one bedroom.

2019 laws say side and rear setbacks can be a small as 4 feet, just enough for fire access. (unless you want more of course.) This is way less than our typical 10-foot side yard setback and the 20-foot rear setback for a new or remodeled single-family home.

2019 laws reduced the planning review period from 120 days to 60 days.

2019 laws say cities and utilities can now impose ‘proportional’ impact fees on ADUs greater than 750 square feet. Lalahpolitico: This was ambiguous before, and it does make sense to support infrastructure. So fine.

All of this means there are a whole lot of people who couldn’t build an ADU in Los Altos before, who can build now. Of course, there are more details to sort out.  Get at least some of your questions answered at this event…


FEB. 27, 2020

There is a LACY event February 27, 2020, featuring Guido Persicone, Planning Services Manager, City of Los Altos.  From 5:30 to 6:30 pm  6:15 to 6:45 pm he will EXPLAIN the revised ADU rules in some depth. At 7:00 pm there is a panel that will introduce some lending and construction options of interest to City of Los Altos homeowners who want to build an ADU in Los Altos. After the panel presentations, there is a period for mingling with the panelists and asking questions. You can learn more about how to move forward with the planning permit process and how to finance your project.

Free Eventbrite registration here. Registration is not required but appreciated.

Location: Los Altos Youth Center, 1 N. San Antonio Road, Los Altos.  El Camino Hospital Mountain View, Main Hospital Conference Room,2500 Grant Road, Mountain View, CA 94040. Note: Parking can be difficult, especially at 5:30 near the YMCA there. Carpool?

View Map

ADUCollective website photo

If you want to match your main house you will need an architect. Here’s an ADU design from ADU Collective, photo from that website.


5:30 – 6:30pm  6:15 – 6:45pm
Update on state laws regarding ADUs, led by Guido Persicone, Planning Services Manager, City of Los Altos

6:30  6:45- 7:00pm:
Complimentary light refreshments

7:00 – 7:45pm:
Welcome, panel presentation, and general questions moderated by Cathy Lazarus

  • Jon Biggs, City of Los Altos – City of Los Altos Development Director
  • Jessica Resmini, ADU Collective – architect for custom design ADUs
  • Greg Popovich, Goldbar Builders – ADU specialist builder – onsite
  • John Geary, Abodu – provider of pre-fab ADUs
  • Fathia McCauley, Housing Trust Silicon Valley – ADU construction loans

7:45 – 8:30pm:
An opportunity for individual conversations with panelists and their colleagues about rules and regulations, design, construction, and financing.

Lalahpolitico Analysis:

The only people who can really say exactly what the new State rules mean in Los Altos are Mr. Persicone, Mr. Biggs and our City housing attorney. Lalah has a pretty good idea, as do the RESOURCES below…but the interpretation devil is in the details. I hope this event Feb. 27  illuminates us all.  Here is my thinking now…

The 2019 State Law changes make it marginally easier to build an ADU in Los Altos. But for units over 750 square feet, costs may be higher than under the old regime.

A lot of neighbors will be shocked if their neighbors actually use the 4 feet side/back ADU setbacks and that becomes the Los Altos norm.  Essentially ADUs are being treated more leniently than new Accessory Structures – you know, workshops, sheds, pool houses.

Lalah wonders if the City Council will now need to rewrite the City’s own ADU ordinance and the Accessory Structure ordinance. [The City Council of Los Altos Hills has started to consider possible options for countering the 4 foot set back vs. their usual 30 foot setbacks. ] And then there is still more zoning work for City Staff just ahead… MTC/ABAG/HCD is likely to triple the City’s RHNA Housing Production target, if Los Angeles is an example of what is coming. Surely something has to be upzoned somewhere in Los Altos?.

Some of us had been wondering if the really crazy radical part of SB50 – 4-plexs on any single family lot in the entire state – was going to fly in the Sacramento legislature.  If a revenue-seeking person could build a four-plex on their lot, why not wait for that to be allowed, instead of moving forward with a mere ADU? Actually the 4-plex threat disappeared from the bill well before the final voting last month. But see AB1289.

[Updated:] Yet the City of Los Altos could do more to incentivize ADU’s. On one-acre+ lots why not consider allowing multiple units attached to each other and perhaps also to the main house.  The idea is NOT to place 3 little cottages just anywhere on the acre lot.  Instead put them in one structure, like a large guest house.  Say Max 2400 square feet on any 1 acre lot? Let the owner decide how many units, like 3 at 800 square feet or 2 at 1200? Sensible setbacks…Just asking…[Correction: The City of Los Altos Hills used to allow up to 3 units per single-family home, but that seems to not be the case today.]
Goldbar ADU specialist buildier. An ADU that matches the main house.

Goldbar Builders specializes in constructing custom-designed ADUs that can blend with the main house.


State Law short summary from the Architect – ADUcollective /Feb.10, 2020

State Law long summary from CA Housing & Community Development (HCD) /Feb. 10,2020

Previous Version How to Build an ADU in Los Altos – If you are just starting to learn about single family home residential zoning and building,  this Lalahpolitico article can be a good place to start. There are links to even more  “explainers ” at our website.


Chapter 14.4  Accessory Dwelling Units – of the Municipal Code [out-of-date?]

All Ordinances:

In all ordinances above, you can find Chapter 14, and zones for single-family homes by size range of the parcel 10, 20, 40. Those numbers refer to the typical size of lots in that zone, smaller to bigger.

Most common SFH zone is R1-10 Single Family District.   When you find the relevant size of your house parcel, you can find out about setbacks and lot coverage that apply to YOU.

As of 2020 the following is apparently not necessarily true if you want build an ADU in Los Altos …”If you recently rebuilt the home on your parcel with the maximum house size allowed in the ordinance, you will not be able to add an ADU.  There is no free lunch. If you have not already built out to the max, other constraints apply.” Talk to the Los Altos Planning Department.


For an explanation of how Los Altos regulations on setbacks and LOT COVERAGE affect the feasibility of an ADU in your situation, take a look at our prior posts. Our city council was moving towards an 800 square foot size limit on Accessory DWELLING units over months and months of delay caused by rewriting the Accessory STRUCTURE ordinance. (These are workshops, pool houses, etc.) At the September 2018 council meeting, the majority vote suddenly swung to a 1200 square foot ADU limit for all parcels provided that the parcel could conform with the other conditions.

1) For an explanation of setbacks, lot size and LOT COVERAGE prior to the 2019 State Laws see (With the 2020 State Law, this is the significant part that has changed – a city can no longer use lot coverage and big side and rear setbacks to ‘prevent’ an ADU.)

City Improves Incentives for Granny Units in Los Altos

2) For a review of the city council wavering about the terms & conditions in our local ADU ordinance see

Create your granny unit ADU or pool house in Los Altos…

During the long period when the City had no ordinance, the state law applied.


About the author


Norma Schroder is an economics & market researcher by trade and ardent independent journalist, photographer and videographer by avocation. Enthralled by the growth of the tech industry over the decades, she became fascinated with the business of local politics only in the past several years.