Construction & Remodeling

5-Star Rated Bay Area Construction Experts for Accessory Dwelling Units (ADU) and Room Additions

  • Starting at $44,900

  • Financing Available

  • Engineering Plans & Permit Included

  • Licensed, Insured & Bonded

  • On Time & Within Budget

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Deciding to build an ADU?

An ADU, also known as an “accessory unit”, “second unit”, “in-law unit”, or “granny flat”, is one additional smaller unit on the same property with a single-family home. ADUs are an innovative, affordable and effective option to increase the value and space of your home. ADUs add housing to the community without the need to subdivide the land to create new parcels and can play a key role in meeting housing needs in the community. 

ADUs can take many forms, including new detached units, additions to an existing home or garage, or the conversion of existing space to a new habitable unit. Regardless of the form, a homeowner must work through several steps to legally create an ADU on a property.

How much will it cost me to build an ADU?

We have a portfolio of plans, starting at only $44,900. Typically, detached ADU costs more than attached ADUs. GemBuilt offers various financing options, including ones that leverage the future earnings of the ADU. However if you’re not planning to rent out your ADU or sell your property soon after construction is complete, your household’s cash flow needs to be sufficient to absorb your monthly payment.

Does an ADU increase property value?

To ease the crushing housing shortage in Silicon Valley, laws have changed to encourage homeowners to build accessory dwelling units on their property - to house aging family members, help grown children find a place to live in this challenging rental market or generate extra income using the space over a garage or in the backyard.

Real estate professionals in high tech areas of the West Coast (Silicon Valley, San Francisco, North Bay, Santa Rosa, etc.) report that most of the homes sold in the last year that included a recently constructed ADU more than recouped the ADU project cost in the resale - well beyond, in most cases.

A 2012 study published in The Appraisal Journal surveyed 14 ADU-enhanced properties. The study concluded that ADUs generally contributed about 25% to 34% of each property’s assessed value. Furthermore, adding an ADU demonstrated an average of 51% increase in resale value.

How can GemBuilt help me save money on building an ADU?


We have built dozens of ADUs for our happy clients in the bay area (take a look at our reviews) and we can get started quicker, since we have a portfolio of plans that were already pre-approved by the City.  In addition, units less than 750 sq. ft. will cost less to build, and in accordance with state law, as of Jan. 1, 2020, these smaller units will not be subject to impact fees such as parkland and school fees.  

What permissions do I need in order to begin building? 

Once you have determined what type of ADU you want, we take care of all regulatory requirements. We will ensure a building permit in comply with the zoning code. Certain ADUs inside the Coastal Zone may also require a Coastal Development Permit, processed at the same time as the Building Permit application.

If your parcel is zoned Commercial Agriculture (CA), GemBuilt will also obtain approval of a discretionary land use development permit from the County, which involves public notice to your neighbors. Some projects may also require additional permits related to grading or any septic upgrade that might be necessary. If you are designing an ADU that exceeds any of the site or dimensional standards, you also may need a discretionary development permit. 

Why should I contact GemBuilt for my ADU / Room Addition?


You need a reliable builder, who knows how to get things done at the highest quality, on time, and on budget.  That's what you'll get. The highest rated builder in the bay area. Period. 

  • We have multiple Financing options, including $0 down, 0% interest.

  • 14 years Experience & 13 Awards.

  • 5-Stars Reviews on Houzz, Google and Angie's List.

  • Dedicated Project Manager.

  • Licensed, Insured and Bonded.