ADU in Los Gatos CA - Living Dining areas - unit over garageWhat is an ADU? This lingo may crop up in housing conversations and leave some hearers baffled, though it’s been in the news quite a lot in recent years.

ADU explained

ADU stands for Accessory Dwelling Unit. In the past, They may have been called:

  • Granny Unit, Granny Cottage, Granny Pod, or Granny Flat
  • In-Law Unit or Mother-In-Law Unit
  • Guest Cottage
  • Carriage House
  • Secondary Dwelling Unit
  • Accessory Dwelling Unit or just Accessory Dwelling

This structure is usually a stand alone, detached building near a primary single family home. It should have its own kitchen, private bath, outside entrance, and a place for a bed (or a Murphy bed or sofa bed, if it’s more like a 1 room studio).

Sometimes, though, the unit is above a garage or attached to the primary home. In 2021 I sold a Los Gatos home that had a guest suite over the garage (see photo above). In short, you could be considering an attached ADU or a detached ADU.

A detached unit cannot exceed 1200 SF of living space. It could be one story, or two!

Junior ADUs

A Junior Accessory Dwelling Unit, often abbreviated to JADU but sometimes called Jr. ADU, is one which is attached and usually smaller in size. The State of California defines them as:

Junior Accessory Dwelling Units … are allowed to be created within the walls of a proposed or existing single-family residence and shall contain no more than 500 square feet. JADUs offer additional housing options. They may share central systems, contain a basic kitchen utilizing small plug-in appliances, may share a bathroom with the primary dwelling, all to reduce development costs.

These are sometimes conversions from large suites or bedrooms in the house and don’t change the overall square footage. The could also be garage conversions.

The Town of Los Gatos has a little different, but similar info:

(it) does not exceed 500 square feet and is contained within the existing or proposed space of a primary dwelling or ADU. The square footage of a JADU counts against
what is allowed for the residence, ADU, or combination of both. (It) must include its own cooking facility with appliances, and a food preparation counter and storage cabinets. If the JADU is contained within the proposed or existing space of a primary dwelling, it may include separate sanitation facilities (bathroom), or it may share sanitation facilities with the primary dwelling. If the JADU is contained within the proposed or existing space of a detached accessory dwelling unit, it shall include separate sanitation facilities.

The last line states that the junior accessory dwelling unit can be attached to a detached cottage, rather than the primary single family home. It is possible to have a house, a detached cottage, and attached to that cottage yet another smaller living space. Yes, three units on one lot in Los Gatos is possible – as long as there is enough land for it. This may be the case throughout the state, but I’m not sure.

There’s a formula that city and town planners use to decide how much of a parcel of land can be covered by living space. It is called the Floor to Area Ratio, or FAR. It also includes how much of the land is covered by concrete or other impermeable surfaces. When it rains, the water needs to be able to sink into the ground and not just go down the gutters to the bay and out to the ocean. For that reason and others, the ratios of open space and built over space are carefully regulated.

Efficiency Kitchen Alternative (Santa Cruz County)

In Santa Cruz County, they have a 3rd category, or subset of the Junior Accessory Dwelling Unit, called the Efficiency Kitchen Alternative.

Plusses of a guest cottage

There are so many advantages of having a secondary dwelling unit for homeowners and also for those who rent or enjoy them, such as increased privacy for extended family members who want to be close, but not “too close”. Clair and I have had clients seeking to buy a home with a granny flat or to buy a duplex just for separate kitchens!

The guest cottage can be a great income source, too. In the San Jose area, these often will rent for upwards of $2,000 (and more in Campbell, Saratoga, Los Gatos, and Monte Sereno). Naturally, it depends on the size, condition, and other amenities, such as parking and having outdoor space.

For renters, a guest house is much nicer than an apartment, particularly if a quiet living space with less density is important. Often there’s some sort of balcony, porch, or yard, too. For folks with dogs, having a bit more outside space can be a big boon.

Costs, financing, and grant money

Depending on many factors, such as slope of the land, proximity to utilities, square footage, finishes, appliances, and other things, ADU construction can run $500 per square foot and up for most people in Silicon Valley. Purchasing a modular home (premade but assembled on site) is likely to be affordable.  Converting a garage or a large room to an attached living unit with an outside entrance will cost much less, of course.

Once you know the size of the home you’d like to construct on your land, you’ll have the starting point for comparison shopping.

There may be some economic help for you, too. The state’s Housing and Community Development page has information on funding and grant money that may be available for those wishing to construct the guest unit. If you are considering building an extra unit, be sure to check out the CalHFA ADU Grant Program, which “provides up to $40,000 in assistance to reimburse homeowners for predevelopment costs necessary to build and occupy an ADU.” Learn more HERE.

ADU financing may be easier than you think! Before any laying any money down for building an ADU, be sure to check with your municipality to see what is required for doing so in your area.

Where are they to be found?

ADU in the side yard of a home on a pie shaped lot - words ADU IN SIDE YARD on bannerHomeowners with large enough parcels are adding these ancillary living spaces in droves, encouraged by changed laws trying to foster more housing across the Golden State as well as some financial incentives to do so.

In Silicon Valley we are finding them all over. Some lots are not huge, but may have wide side yards (as with the photo at left) or very deep lots that can accommodate a standalone ADU.  Sometimes the lots are quite deep, and the cottage can be put at the far back of the lot. In some cases, a detached garage can be converted to a guest cottage – possibly to be rented out and provide another stream of income.

No matter what, the Junior Accessory Dwelling Unit must have an outside entrance and be connected to another unit, but that doesn’t mean that there must be an interior door connecting the two living spaces.

Adding guest units, whether attached or detached, is supposed to make more housing available. We are seeing new home subdivisions including attached secondary living spaces on the ground floor or upstairs over a garage. The financial incentives do help to make these more available.

The question is how many home owners will rent them out, and how many will use them for a home office? That answer is yet to be known.


Related Reading

What is a preliminary title report? Why does it matter?

What is a cripple wall? (on

Learn about the California ADU programs on the Department of Housing and Community Development page