Building an ADU in the Bay Area

As the demand for housing across the Bay Area continues to expand, so has the initiative across multiple counties to make it easier to add an ADU onto new and existing property.  An ADU is short for accessory dwelling unit – a second place of resident on the same piece of land.  They are also commonly referred to as ‘granny units’ or ‘guest cottages’.  Whether the addition of an ADU will be for private use, or as an additional source of income, we can help.

The ability to build an ADU is subject to local jurisdiction and zoning regulations, however it is becoming easier to do across the state as cities and counties adopt ordinances allowing ADU builds.  See the California Department of Housing & Community Development website.

California recently passed Senate Bill SB-9 that allows lots to be split in order to build more dwellings on a lot.

Attached ADU

The topic of adding an ADU, or building a new home with an ADU, has become much more frequent of late.

The home design team at Christopherson will often incorporate attached ADUs into a new home plan.  An attached ADU is a separate mini residence under the same roof.  Intrinsic to the primary home plan, you’ll find shared walls but perhaps a separate entrance.  Many of our plans offer small sitting areas as well as the option for a kitchenette.  This style of ADU allows for flexible living options, and immense privacy for periodic guests.

If adding an attached ADU to an existing home, a home owner could either reconfigure the interior space by way of a whole home remodel, or add on additional square footage for the ADU via a home addition.  Or both!  Christopherson Builders has a limited capacity to offer whole home addition and remodel services.  One fundamental criteria that we have for taking on remodels and additions is that the home we are working on be vacant while work ensues.  Please contact us for availability.

Detached ADU

Alternately, a detached ADU is built as a stand alone and separate residence from the main structure.  This can be a great option for properties with ample building area, and lends itself nicely for uses such as a temporary guest residence or as a potential rental unit.  A detached ADU adds value to the property, and is well within our wheelhouse as it is basically building a new smaller home.  In Santa Rosa CA, an ADU can be up to 1,200 square feet!

Christopherson Builders has several ADU plans available for review, and a couple of plans on our website that are dainty enough to qualify as an ADU.

Planning your ADU

There are a several key factors to research before planning your ADU.  First, understanding the zoning restrictions, location of any easements and the size of the general building envelope will largely determine what can or cannot be constructed.  Once that is known, determining the available capacity for utilities such as water and sanitation will also factor in, or septic capacity if you are on such a system.  The number of bedroom can impact the ADU overall size.

The question we get all the time is – how much does it cost?

And we get it, cost to build is a pertinent and reasonable question to ask.  The thing is, it is a very hard one to answer.  How much something costs to build is really not possible to know reliably until there is architecture which includes structural & foundation plans that can be estimated.  Just like building a home, the style of ADU plus the finishes will drastically impact the price.  We can tell you this, smaller homes are more costly on a dollar per square foot basis than larger homes.  So a very small ADU will have a much higher associated $/SF than a 3,000SF home – generally speaking of course.  That is because foundations and roofs are expensive, as are kitchen and baths.  A small home or ADU does not have the benefit of economies of scale, so they are pricier to build than their larger home counterpart.

Depending on the home plan and scope of work, building an attached ADU is likely to be less costly than a detached ADU.  That said, the return on investment is likely to be larger on a detached ADU.  Plus if you are in it for the long term, a detached ADU will probably be the more comfortable option for privacy and livability.

In both Sonoma County, Vacaville and Napa we are building more and more ADUs along with building main homes to help people maximize the value of their property. Customers often want them for supplemental rental income or in anticipation of a parent or adult child, or caregiver, coming to live with them.   If you are thinking about building a home, consider if an ADU would improve your property value and your lifestyle!