Multi-Family vs Accessory Dwelling Unit (ADU)

The Problem

"I have two houses on my property and I need to know what I have.  Is this a duplex?  Is this a guest house?" 

I get asked this question at least once a week.  It is an issue that often stumps homeowners, realtors, and lenders alike, and is one that doesn't always have an easy answer.  Before I get into the confusion surrounding this topic, I'll clarify some definitions.

Accessory DWELLING Unit (ADU)

They have many names: granny unit, granny flat, guest unit, in-law unit, secondary dwelling, cottage, etc.  Whatever you call it, it can be a great secondary space for renters, guests or family. An ADU is "a secondary dwelling unit with complete independent living facilities for one or more persons that can be attached or detached from the main home."  ADU's are typically smaller in size than the main structure on the parcel and are usually allowable on parcels that are zoned for Single Family Residential.  In Nevada County, "Accessory-Second Dwelling Units" are allowed on parcels within the R1, R2, R3, RA, AE, AG, FR and TPZ zoning districts.  There are various standards, but in general, an ADU cannot exceed 1,200 sq ft of living space.  The state of CA also has a classification of a Junior Accessory Dwelling Unit (JADU) in which the secondary dwelling does not have a kitchen.  It's always best to check to see what the local jurisdiction allows for each parcel.  The Nevada County Accessory-Second Dwelling Unit guidelines can be found at HERE.  Further information from the State of California Department of Housing and Community Development can be found HERE.


A multi-family residence typically refers to a duplex, triplex, fouplex, apartment building, etc. Think of a traditional duplex with two units side by side that are exactly the same. The few multi-family dwellings in Nevada County are typically located within the city limits of Grass Valley and Nevada City, and are specifically located in areas that are zoned for multi-family residences.  In Grass Valley multi-family zoning is R-2, R-2A, R-2A-MH, R-3 and R-3-MH.  In Nevada City, multi-family zoning is R-2.  Both Grass Valley and Nevada City have historical districts which may allow for multiple uses including commercial or multi-family residences.  I have included links to the zoning maps for Grass Valley and Nevada City.

The Confusion

The first thing I do when trying to classify additional living space on a property is look at the public records.  There are numerous sources for public records including Realist, RealQuest, ParcelQuest, and title company searches.  Realist is accessible through the Nevada County Association of Realtors MLS.  Realist provides the lot size, square footage of the home, zoning, type, and land use. 

If a property is a true duplex with two units side by side that are exactly alike, Realist reports the type as 'Duplex' and the land use as 'Multi-Res - Duplex/3-4 Units.'  Seems easy.  However, Realist will also report the same classification for all properties that simple feature an ADU.  I recently received an order for a 3,000 sq ft main home located on a 4+ acre parcel with a 500 sq ft ADU.  Realist types this as a duplex.  This is where the confusion comes in.

The Answer

The answer ... as it always is in real estate ... it depends, usually on the location and zoning of the property.  If the property is located outside the city limits, zoning only allows for Single Family Residential homes (plus an ADU).   The planning department doesn't allow for true duplexes outside the city limits. If the subject is within the city limits of Grass Valley or Nevada City, however, you'll have to dig a little deeper.  You'll need to check the zoning of the parcel to see what's allowable, but typically, if there is a larger home featuring a smaller secondary living space, its an ADU.  If both units are similar in size (possibly attached to each other) and located in an area which allows for multi-family, it's probably a duplex or multi-family.  The planning desks in Grass Valley and Nevada City are always great resources.  

Bottom line,  a concrete answer to this confusing issue can take some additional research.  We live in a community where building started in the 1850's, long before incorporated cities, zoning codes and planning departments.  Back then, landowners milled the wood and built wherever and whatever they saw fit.  What makes this area's real estate so unique is what can make it difficult to assess. 

I am always happy to assist with this issue or anything else related to Nevada County real estate.  Be sure to check out the Nevada County Market Updates, this month I've highlighted the markets of Penn Valley, Rough and Ready and Smartsville/Big Oak Valley.

Call or text me at 530-632-3428.  


Housing Data since 2000 in Nevada County

Housing Data since 2000 in Nevada County

Size Matters