When Building An Adu Do You Need Septic Tank Bigger? (Correct answer)

So if it’s 400 or 500 feet of leach lines, you’re gonna need to have additional area available for that another four to 500 feet and that’s so if your primary septic system fails, you have space to put in a new system.

  • If you have a septic, thats not gonna happen. They are sized to the primary dwelling only, with no expansion. You would have to attach to the city sewer system to do an ADU. Which our neighbor just did as a DIY GC, and built an ADU. 45K for the sewer attachment of both structures, and another 225K for the 500sf structure.

How big should a septic tank be for a 3 bedroom house?

The correct size of the septic tank depends mostly on the square footage of the house and the number of people living there. Most residential septic tanks range in size from 750 gallons to 1,250 gallons. An average 3-bedroom home, less than 2500 square feet will probably require a 1000 gallon tank.

What determines how big a septic tank a house needs?

The larger your home, the larger the septic tank you’re going to need. For instance, a house smaller than 1,500 square feet usually requires a 750 to 1,000-gallon tank. On the other hand, a bigger home of approximately 2,500 square feet will need a bigger tank, more than the 1,000-gallon range.

How big should a septic tank be for a 2 bedroom house?

The recommendation for home use is a 1000 gallon septic tank as a starting point. The 1000 gallon size tank is a minimum and *can be suitable for a 2 bedroom, 3 bedroom house. Some recommendations say to add an extra 250 gallons of septic tank capacity for each bedroom over 3 bedrooms.

What do I need to know before building Adu?

5 Things to Know Before Building an Accessory Dwelling Unit (ADU)

  1. An ADU can have similar benefits to an addition.
  2. An ADU must be habitable.
  3. An ADU can be a good investment.
  4. It gives family and guests comfort and privacy.
  5. In California, an Addition or an ADU are some of the best ways to gain more space at home.

How much does it cost to pump a septic tank?

How much does it cost to pump out a septic tank? The average cost is $300, but can run up to $500, depending on your location. The tank should be pumped out every three to five years.

What is the smallest size septic tank?

If you’re looking to install a septic system, the smallest tank size you’re likely to find is 750-gallon, which will accommodate one to two bedrooms. You can also opt for a 1,000-gallon system, which will handle two to four bedrooms.

How deep should a septic tank be?

Septic tanks are typically rectangular in shape and measure approximately 5 feet by 8 feet. In most cases, septic tank components including the lid, are buried between 4 inches and 4 feet underground.

How often does a 1000 gallon septic tank need to be pumped?

For example, a 1,000 gallon septic tank, which is used by two people, should be pumped every 5.9 years. If there are eight people using a 1,000-gallon septic tank, it should be pumped every year.

How big is a septic tank dimensions?

A typical residential septic tank is usually about 4.5 feet wide x 8.0 feet long x 6 feet tall. Your septic tank may be a different size however.

Can you have a septic tank without a leach field?

The waste from most septic tanks flows to a soakaway system or a drainage field. If your septic tank doesn’t have a drainage field or soakaway system, the waste water will instead flow through a sealed pipe and empty straight into a ditch or a local water course.

How do you calculate septic tanks in liters?

How to calculate the size of septic tank you need. C = 2000 litres + 180P. C = 2000 litres + 180 × 4 = 2720 litres, For 4 users, minimum size of septic tank could be 2.2m × 1.0m × 1.30m (7.2ft × 3.3ft × 4.25ft) in respect to their Length, breadth and depth.

How long do septic tanks last?

A septic system’s lifespan should be anywhere from 15 to 40 years. How long the system lasts depends on a number of factors, including construction material, soil acidity, water table, maintenance practices, and several others.

How is Adu calculated?

Value of ADU after compilation — To estimate the property’s value increase after the construction of the ADU, we multiply the property’s per-square-foot value by the total size of the addition, and calculate 70%-90% of this product. In this case, the estimated value increase is 90% of ($344sq. ft.

How close to the property line can I build an ADU?

Most single-family homeowners can build ADUs A detached ADU will need to be at least 10 feet from the main residence and 5 feet from any property lines.

Can Adu be 2 stories?

A new ADU, however, can take many forms. It can be attached to an existing home, attached to a garage in the rear of the lot, or detached completely. It can typically be one or two stories, with a maximum height of either 16′ or 25′ (depending on location).

Septic System for an ADU: What You Need to Know

When it comes to designing and building a guest home, one of the least glamorous aspects of the process is determining whether or not your accessory housing unit will require a septic system. Despite the fact that many individuals have a broad understanding of what a septic system is, the specifics of what is required to accommodate an ADU are sometimes confusing. So, let’s speak about septic tanks!

What is a septic system?

A septic system is nothing more than a method of discharging waste into the ground. Septic systems, which are more formally known as underground waste treatment systems, are designed to get rid of all the junk that doesn’t belong in your new ADU’s yard or below it. Septic systems are also known as septic tanks in certain circles. It is most frequent in rural locations, where sewage lines are difficult to reach, for septic systems to be installed. No matter whatever type of septic system you pick, each one will have a septic tank as well as a drainfield to collect waste.

If you have ever owned or utilized an RV, you have almost certainly dealt with a septic tank at some point.

Liquid waste will run through the tank and into the drainfield, which is the second portion of your system to be constructed.

What are different types of septic systems and how much do septic systems cost?

The system you pick will be determined by a variety of criteria, including the location of your land, the quantity of space available, and the condition of the soil in your region. The cost of septic tank installation varies depending on where you live and what state you live in. California residents in San Diego and other big cities may anticipate that the procedure and installation will be more expensive than in other regions of the state. A reputable septic contractor will clarify any issues or obligations that may emerge as a result of the various system configurations.

Leach Field

A classic septic system, so named because of the fact that it is the most common configuration of septic tanks and leach fields, is one that is commonly seen. A leach field is the most environmentally friendly way of waste distribution because it allows for the recycling and replenishment of liquids back into the ecosystem through the use of perforated pipes, making it the most environmentally friendly type of trash distribution. These systems are also the most cost-effective, with design and installation for a system large enough to support a standard ADU typically costing between $25 and $30 thousand dollars on average.

Certain parcels pose difficulties for a typical leach field to manage. There are a variety of alternate septic seepage systems that may be used in these scenarios.

Vertical Seepage Pit

A vertical seepage pit functions in a similar way as a leach field, with the exception that a big concrete cylinder replaces the whole field of pipes. In most cases, this approach is employed in instances when the amount of accessible land on the site is insufficient to accommodate a leach field, which can be fairly big in size. The pit is typically sunk approximately six feet beneath the surface of the earth and continues deep into the ground, where microorganisms are responsible for the complete decomposition of garbage.

Vertical seepage pits are frequently permitted only in coastal environments where groundwater is combined with and cleaned by saltwater, rather than elsewhere.

Horizontal Seepage Pit

Due to the fact that these pits are fairly identical to their vertical counterparts, there isn’t much more to say about them. Note that horizontal seepage pits require deep soil and strong percolation, which will be discussed more in the section on horizontal seepage pits. Seepage pits, both horizontal and vertical, are far more expensive than leach fields, costing between $60 and $70K, and are only utilized in regions with limited available space.

Do all ADUs need a septic system?

No! Septic systems are only required if your property is not linked to a public sewage system such as the city sewer system. If this is the case, you, as the property owner, and your septic system are solely responsible for waste disposal on your land. In more rural regions, where a central sewer system is either impractical or impossible to connect to (or a combination of both), this is the most prevalent scenario. In the event that you reside in one of these places, it is probable that you are already familiar with septic systems and may even be in possession of one of your own.

Can I use my existing septic system for an ADU?

It is dependent on the situation. The most probable response would be “no,” because most main-house septic systems are not large enough to handle both a primary residence and an ADU on the same property. However, if you are confident in the performance of your current septic system, the best course of action would be to explore this issue with your contractor and determine what your alternatives could be.

How long does it take to add a septic system?

In order to proceed, you must first have your septic system certified by the Department of Environmental Health in your local jurisdiction. It might take anywhere from 60 to 90 business days to get your septic plan approved once you have submitted it. After that, the building process will take around two weeks. The system is then connected to the plumbing system in your ADU, which completes the last stage. Prior to submitting a septic design, there is some preparatory work that must be completed, the most important of which is a feasibility study to assess whether or not a septic system is necessary in your location.

In order to prevent rubbish from piling up on your property, this is a very necessary step.

Fortunately, all testing will be completed well before any actual work on your land begins, as will the remainder of the essential feasibility studies, ensuring that the least amount of money and time is wasted.

This first step will point you in the direction of the system that will work best for your budget and property while also making the building process as easy as possible.

Coastal Commission has decided to reduce off-street parking restrictions for accessory dwelling units (ADUs) in the Coastal Zone as of August 2021, except where the accessory dwelling unit is located in an area with restricted parking or within 500 feet of the coastline.

Do ADU’s Need a Separate Septic System?

Accessory Dwelling Units (ADUs), often known as granny flats or in-law apartments, are a fantastic option for cheap housing, particularly in locations where the real estate market is overheated (and limited housing supply). Located on the same property as the original house, these flats serve as a secondary residence for aging relatives, adult children, and low-income families who need a place to stay while visiting. Since the State of California altered its zoning restrictions to make ADU construction easier and more permissible, it has become a popular alternative for households and prompted a number of questions concerning the building process.

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We’ll go through the specifics of septic systems for accessory dwelling units (ADUs) so that you can make an informed decision about whether or not to build a supplementary apartment on your property.

Because septic systems are normally designed to accommodate the whole number of residents in a family, ADUs will require a separate system because the principal dwelling’s system will not be able to accommodate the extra occupants in the ADU.

These tasks must be completed before applying for any building permits to ensure that your site can meet the standard building guidelines as well as the local plumbing code.

The septic professionals at Acuantia can assist you with this procedure, which includes the following steps: Tests on the soil, including soil depth measurements and percolation tests (to determine the rate at which soil absorbs water) Review of limiting conditions (such as impermeable soil and high groundwater levels) Verification of availability of disposal area for system installation or replacement Maintaining setback clearance requirements Review of physical site features of the lot and area adjacent to the disposal system A successful evaluation will allow homeowners to pick the suitable septic system for the ADU site design and install it on their property.

The septic contractor will discuss your alternatives with you, which may include a leach field or seepage pit septic system, depending on the construction site and available space.

The entire process of applying for and gaining official permits takes time, so you’ll need to factor this into your budget and project schedule.

Our skilled staff collaborates with you and all types of developers in order to save you both time and money on your septic system installation and maintenance. Please get in touch with us right away if you require any further information about our services.

How To Add An Accessory Dwelling Unit

The eAccessory dwelling units (ADUs) are in high demand throughout the country, and this 480 sq. ft. contemporary cottage lives large thanks to the e (see anmore on the subject here). As homeowners scramble to construct them, cities and counties are changing zoning regulations to allow them to be built. In addition to using ADUs as homes for aging parents or caregivers, an increasing number of homeowners (particularly those in neighborhoods with a cool, walkable, urban vibe) are using them as long- and/or short-term rentals to supplement their income.

  1. As for the ADU boom in Austin, Lévy is noticing an interesting new trend: some people are building a primary residence as well as an ADU on the same lot and selling the two residences to two different buyers without subdividing the lot.
  2. He anticipates that this will continue in the future.
  3. Establish a budget and make arrangements for financing.
  4. Employ an architect if you are constructing an ADU in a city such as Austin, which has a large number of complicated zoning codes and constraints to contend with.
  5. Lévy, who has extensive experience dealing with these regulations, claims that the codes are sometimes written in a vacuum, without taking into account the impact of the codes on one another.
  6. A person (for example, an architect) who is skilled at recognizing how these codes interact is required.
  7. Determine where you will be able to construct.

For the Kitsap County Department of Community Development in Washington State, “unincorporated areas are organized by zoning categories,” explains Natalie Kuzmick, an education and outreach technician for the Kitsap County Department of Community Development.

As of January 1, 2018, ADUs are permitted (P) in Kitsap County in both urban low-density and urban medium-density residential areas.

In order to obtain supplementary permits, additional fees and reviews must be completed, and neighbors must be notified in writing before a permit can be issued.


You can’t just go out and build whatever size ADU you want in any location you want.

For example, in Kitsap County, only one accessory dwelling unit (ADU) is permitted per lot; the property owner must reside in either the primary residence or the ADU; the ADU cannot exceed fifty percent of the habitable area of the primary residence or nine hundred square feet, whichever is smaller; all zone setbacks apply; the ADU must use the same side-street entrance as the primary residence; and the ADU necessitates additional off-street parking for the primary residence.

  • Prepare to either comply or risk having your permit denied.
  • Pay close attention to the details.
  • Depending on whether or not your property is on a septic system, you may be required to construct an additional septic system to accommodate the ADU.
  • Look for design inspiration.
  • Michael Litchfield’s book In-laws, Outlaws, and Granny Flats: Your Guide to Turning One House Into Two Homes is a good place to start your research.
  • The New Small House by Katie Hutchison,Small Houses (Great Houses) by the editors of Fine Homebuilding, and Accessory Dwelling Units: Case Study by the United States Department of Housing and Urban Development and Sage Computing Inc.
  • To examine a variety of designs appropriate for use as auxiliary dwelling units (also known as granny apartments or granny flats), such as Plan 484-4, which is displayed in the perspective and deck views, as well as at the top of this post, please visit this page.

Create a rough sketch of your concept.

You and your architect may both refer to it, and you can use it as a starting point for the next phase, which is a meeting with a city planner to talk about the project.

Arrange a meeting with a municipal planner.

According to Lévy, establishing a preliminary ADU design and paying for a one-hour consultation with a city planner in Austin is a good idea.

Basic queries, such as the number of parking spots you are obliged to have, can be answered for free by Austin city planners; however, deeper questions will require a paid consultation with a city planner.

Some planning offices may provide you the opportunity to speak with a planner at no cost.

Submit the final application, which typically includes documents such as a legal description of the property, a site plan, a plat map, a project application, supplemental applications, additional permits (if necessary), address verification documentation, sewage disposal and water supply documentation, floor plans, and photographs of the property, among other things.

Please keep in mind that certain towns and counties will accelerate the examination of your permit application for an extra price, which may be worth it in certain cases.

Become a professional.

Before signing any contracts, consult with an attorney to ensure that they are in your best interests.

As soon as you acquire your building permission, you should begin work. And don’t forget to congratulate your success in obtaining a building permit. You’ve earned a small victory dance for your efforts. To view a collection of one-bedroom home plans, please visit this page.

What are the 10 Things to Consider Before You Build an ADU?

If you’re a homeowner in California, it’s likely that you’ve heard of the concept of creating Accessory Dwelling Units (ADUs), which are separate dwellings that are built on the same land as the primary residence. These small dwellings, which are also known as granny flats, in-law apartments, backyard cottages, or simply ADUs in California, can be used for a variety of purposes. They can produce rental revenue, provide housing for aged parents, grown-up children, and lower-income households, among other things.

When it comes to building an ADU in California, now is an excellent time to do it.

Don’t expect to build a modest back home in your backyard to be a piece of cake, though.

That is why we have compiled the ten suggestions listed below to assist you in the construction of your ADU project in California.

1. Is the Property Eligible for Building an ADU?

Check the development standards for your area to see if your property qualifies for the construction of an ADU. Before you begin designing an ADU in California, check to see if your lot qualifies for construction under the state’s local development regulations. Here are a few things to keep in mind: Density. This refers to the maximum number of residential units that can be built on a piece of land. Make certain that your proposed ADU is compatible with the density restrictions imposed by your municipality.

  1. The height of new structures in your neighborhood might be limited by your city or county.
  2. Setbacks.
  3. When building an ADU in San Francisco, for example, your rear setback might be as much as 25 percent of the lot’s depth, but in Los Angeles, the minimum rear and side setbacks are frequently 5 feet.
  4. Utility easements are a type of easement that allows a utility to be used.
  5. Check to see that your proposed ADU will not restrict access to these services.
  6. The City of Los Angeles, for example, requires that any new building be at least 10 feet away from utility easements; otherwise, a permission from the public utility company would be necessary.
  7. There are a variety of other considerations that may affect your ability to construct an ADU in California.
  8. In San Francisco, there are no restrictions on the size of an ADU’s floor space, as long as it is within the buildable area of the property.
  9. Remember to verify with the building department of the body having jurisdiction over your project to see if there are any other limitations that may apply to your undertaking.

Once you’ve confirmed that your property qualifies for the construction of an ADU addition, you can begin the planning and design process.

2. Would It Need Additional Parking?

Determine whether or not you require more parking. Prior to the passage of 65852.2, towns and counties throughout the state mandated the construction of new off-street parking for an ADU. This situation was particularly difficult to live with on smaller parcels with limited available space. You no longer have to be concerned about finding a new parking place if your property fits ANY of the following criteria: It’s only a half-mile walk to a public transportation system. Moreover, it is located in a historically and architecturally significant neighborhood.

A car-sharing vehicle may be found within a few blocks of the residence.

According to the city of Los Angeles, just one parking space is required for ADUs that do not fulfill any of the exemption conditions listed above.

To be assured, check with the appropriate authority in your jurisdiction.

3. Would Plan Site Access to needed of ththe ADU?

For a variety of reasons, accessibility is an essential element to consider. The first and most important consideration is safety. A clear passage to the street should be available to the occupants in the event of a fire. Consider the walkway: cheap precast pavers will give a handy passage from the street to the ADU without costing a lot of money to install. You should also have a clutter-free passageway between your home and the property boundary, so consider other options for storing your garbage cans if that is where you now store them.

4. How to integrate privacy into the layout of the ADU?

The future resident will have a say in how much privacy is built into the ADU’s design. If your parents are living in the ADU, less privacy may be appropriate in the design. Their front door or porch might be situated such that it faces your rear entry, creating a sense of inclusion and harmony in the living arrangement. Window shades, trees, and plants may all be used to create subtle privacy screens in a home. If you want to rent out the flat, the lack of privacy may be a deal-breaker. Consider the possibility of a stranger residing in your backyard.

Most likely not, and it’s possible that the discomfort is reciprocal.

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Even a few extra efforts may make a significant difference in creating a comfortable living situation for both you and your tenant.

5. What to consider while understanding ADU site conditions?

Is your backyard a level surface or does it have a slope? Is there any rainfall pooling in certain areas of it? Is the soil in the backyard untouched, or has it been filled in the recent past? Site work can account for a considerable portion of the total cost of your project; knowing the answers to these questions before you begin work will help you avoid unexpected costs down the track. Alternatively, if your ADU is going to be built on a slope, you may equal out the grade by digging or support the building from the ground up.

If the ADU’s intended inhabitant is an elderly person with limited mobility, make certain that they can reach to the front door without having to worry about steep inclines or stairwells in the way.

Make certain that any soil that has been previously excavated, scraped, or filled has been replaced with appropriate soil and compacted in accordance with the recommendations of the soils engineer before you begin construction.

If you have drainage problems in your backyard, you should fix them before starting building.

Our team of qualified civil engineers can examine the drainage conditions on your construction site and take actions to prevent drainage-related concerns from emerging during and after the project’s completion. You may connect with specialists for your ADU needs right here.

6. What to consider for Utility Connections in ADU?

Determine whether or not you will be able to tap into existing utility connections. ADUs are not considered “new residential uses” for the purposes of calculating connection fees and capacity charges under Section 65852.2. Typically, they do not necessitate the installation of separate service meters. No new meters are required because water may be obtained from the pipes servicing your home. It is possible to tap into your home’s gas pipes and attach a new private meter “upstream” of the old meter when installing a gas furnace, water heater, or stove.

Furthermore, your present septic tank may not be capable of handling the sewage generated by the construction of extra restrooms.

7. How to verify your ADU Design Guidelines?

The design criteria for ADUs differ from city to city and county to county. Despite this, there are certain common standards, and the architectural style of your ADU will be influenced in part by the California Residential Code. Kitchens and baths are required in all apartments, according to the regulation. Ceilings must be at least 7’6″ in height, and livable rooms must be a minimum of 7′ in each direction in order to be considered habitable. It is necessary to install a heating system for the unit; plug-in space heaters are not appropriate.

Because municipal ADU ordinances may differ in their interpretation of State codes, you should check with your local building authority to acquire a clear understanding of the design criteria for your ADU.

8. How to comply with Title 24 Energy Report and CALGreen Code regulations?

Title 24, California’s Building Energy Efficiency Standards, treat ADUs as if they were brand new residences, according to the state. This means that the exterior and mechanical systems of new, detached ADUs must fulfill all applicable design standards in order to be compliant with the laws. For a more in-depth explanation of them, please see here. The California Green Building Standards Code, often known as the CALGreen Code, applies to ADUs as well. The code specifies a number of building requirements that are intended to reduce the environmental effect of new development while also promoting environmentally friendly construction.

The CALGreen Code includes a comprehensive list of necessary home measures, which may be found by clickinghere.

9. What are the Fire Regulations to Follow?

Consult with your local building authorities to determine whether sprinklers are required in your new ADU. Normally, this is required of all newly constructed units, however the new ADU Act exempts these units from this obligation. In order to be certain, check with the building and fire authority. If your jurisdiction does not need sprinkler systems for ADUs, you may be considering lowering expenses by removing them from your construction plans. Keeping in mind that sprinklers are a crucial safety element in areas where firefighter access is limited, sprinklers are a good choice in this situation.

It’s important to remember to arrange for an escape route.

According to the Fire Code, your ADU must have an unobstructed route to the street as well as a clearly defined pathway to the street. If your parents will be staying in the unit, remember to account for their age and mobility requirements while planning escape routes.

10. How to Save Space in the ADU?

Space is a major problem for those who live in ADUs. When you have to fit a kitchen, a bathroom, a sleeping area, and a living space into 1,200 square feet or less, things may become a little tight. The furnishings, appliances, and storage choices you choose may make a significant difference in the amount of room and comfort you have in these compact houses. When it comes to decluttering, wall-mounted storage is essential, and it works in every region of the unit. Accept it as a fact of life.

  • Upper cabinets and hooks for utensils should be installed in the kitchen.
  • Providing your ADU’s inhabitant with extra wall-mounted storage alternatives will allow them to make better use of their available floor space.
  • A loveseat can be used in place of a traditional sofa.
  • When extra space is required, chairs and tables may be folded to make more room.
  • The same may be said about appliances as well.

Do you want to boost the value of your ADU?

Are you hoping to save both time and money throughout the building process? The 10 suggestions listed above might assist you in finding the proper path. If you want to turn your ADU into a second source of income, check out this post. The structure, however, is not without its difficulties. If you want to obtain the keys to your ideal ADU without breaking the bank, you’ll need a qualified engineering team and a quality, economical builder who will see your project through from start to end, according to the experts at HomeAdvisor.

We are aware of the obstacles that lie ahead and how to overcome them.

Get in touch with Design Everest for a no-obligation consultation and price.

Keep up with us on social media for more updates: Facebook, LinkedIn, and Twitter.

FAQs — Backyard ADUs

Dwelling units known as accessory dwelling units (ADUs) are independent, unique apartments that are erected on single-family or multi-family residential land in some situations. ADUs are also referred to as guest homes, mother-in-law units, granny flats, and backyard cottages, among other terms and phrases. ADUs are classified into two categories: detached units and attached units. A Detached Unit is a structure that is located in a backyard or a side yard on its own.

An Attached Unit is a space within the principal residence, such as an attic, garage, or basement, that is converted into a living area. Accessory dwelling units (ADUs) are described in further detail on the website accessorydwellings.org.


In the United States, hundreds of thousands of ADUs are being built because they are an excellent method to relieve the housing shortage while also generating passive income for their owners. Furthermore, ADUs are less expensive than other types of housing and make more efficient and ecologically friendly use of available land. ADUs also contribute to the development of emerging socioeconomic trends in the United States. ADUs make it simpler to stay in one’s home as you age. They make it possible to live in multigenerational families, which makes it simpler and less expensive to care for elderly parents as they grow older.

Finally, downsizing and minimalist living are popular right now, and the trend is expected to continue to expand in the future.


Many communities, including yours, are revising their zoning restrictions and fees to make ADUs permissible in their neighborhoods. Most governments consider ADUs to be vital to stabilizing rents in quickly developing districts, and as a result, they have amended their zoning ordinances to include them. For additional details, please see ourLocal Rules page.


In the backyard, an ADU is a separate living unit that has the appearance and feel of a house, but is on a smaller size. Our ADU design routes include 1-3 bedrooms and range in size from 450 – 1200 sq ft in floor space, depending on the requirements and the amount of the land on which they are built. The majority of our design pathways have an open concept kitchen/living room space with full-size appliances, a washer/dryer, and 1-2 bathrooms, among other features. Our manufacturing partners produce each item using only the highest-quality materials available on the market.

When it comes to providing seclusion between your house and the ADU, we use both new and existing landscape features to accomplish this.


On the basis of a comparison of the selling prices of single-family and two-family homes, an ADU will almost certainly boost the value of a property because of the potential revenue stream it provides. Backyard ADUs, on the other hand, suggests seeking a second, independent opinion!


In the case of an ADU, there will be a corresponding increase in property taxes equivalent to the amount of the ADU’s assessment as an improvement to the property. In most cases, the inclusion of an ADU should not result in a change in the value of the remainder of the property. However, the homeowner’s property tax bill may still rise as a consequence of the usual yearly increase in taxes and the addition of additional levy levies, which are included in property taxes each year and are not tied to the ADU.


Associated dwelling units (ADUs) obtain sanitary sewage and water service by connecting to the principal residence’s main sewer and water service. The principal residence’s basement serves as the entry point for water and sewer hookups, respectively.

ADUs are connected to current electrical service through a new meter, which allows the unit to be self-sufficient in terms of power costs. Because ADUs do not utilize natural gas, a connection is not required. Heat pumps provide heating and cooling for our ADUs, which are extremely energy efficient.


Sanitary sewer and water service are provided to ADUs by connecting to the principal residence’s main sewer and water line. The principal residence’s basement serves as the entry point for water and sewer hookups. ADUs are connected to current electrical service by a new meter, which allows the unit to be self-sufficient and pay for its own power use. Given that ADUs do not utilize natural gas, a connection is not required. Heat pumps provide heating and cooling for our ADUs, which are extremely energy-efficient.

Accessory Dwelling Units

Dwelling units that are attached to another primary dwelling unit in most residential, mixed-use, and agricultural zones are known as accessory dwelling units (ADUs) or accessory dwelling units (ADUs). Permit Sonoma’s ADU Checklist is available for download. Accessory Dwelling Units and Junior Accessory Dwelling Units are two types of accessory dwelling units.

ADU Rescue!

Do you have an unpermitted Accessory Dwelling Unit (ADU) or Junior Accessory Dwelling Unit (JADU) and require an extension of time to complete an enforcement violation? Learn more about how you may be eligible for an extension and how to apply for our ADU Rescue program by visiting our website.

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UpdatedADUandJADUOrdinance Effective October 14, 2021

ADU and JADU laws were revised by the Sonoma County Board of Supervisors on September 14, 2021, according to the county’s Zoning Code, which was authorized on that day. ADU Ordinance (ADU Ordinance) Ordinance of the JADU

Development Standards

The following are some of the most important criteria that property owners should be aware of while planning an ADU project. Please refer to the Zoning Code and the Permit Sonoma ADU Checklist for a comprehensive list of development criteria. Please keep in mind that the standards listed below apply to inland zones. See Section 26C-325.1 of the County’s Coastal Zoning Ordinance for information on the requirements for accessory housing units in the Coastal Zone.

Permitted Zones

The following are some of the most important criteria that property owners should be aware of while preparing to build an ADU project on their land. The Zoning Code and the Permit Sonoma ADU Checklist include a comprehensive set of development regulations. Please note that the standards listed below are applicable to inland zones only. Section 26C-325.1of the County’s Coastal Zoning Ordinance contains requirements for accessory housing units in the Coastal Zone.

ADU Exclusion District

Accessory dwelling units (ADUs) are prohibited in the Z Accessory Dwelling Unit Exclusion Combining District if there are natural dangers, public safety concerns, water availability or water quality concerns. As of 2019, the County has reevaluated the applicability of this district and has subsequently rezoned approximately 1,900 properties to eliminate the Z Combining District and enable ADUs to be used as a permissible use. Parcels that have not been rezoned but still include this Z Combining District may be eligible to seek for a change in zone classification.

The project must be examined and approved by the Planning Commission before being considered by the Board of Supervisors for final approval. More information on submitting an application for a zone change may be found here. Verify the zoning of your property.

Number of Units Permitted

There are no ADUs allowed in the Z Accessory Dwelling Unit Exclusion Combining District if there are natural dangers, public safety concerns, water availability or water quality issues. As of 2019, the County has reevaluated the applicability of this district and has subsequently rezoned approximately 1,900 properties to eliminate the Z Combining District and enable ADUs to be used as an allowed use. Zoning changes may be requested for parcels that have not been rezoned but still contain the Z Combining District.

Before being authorized by the Board of Supervisors, the project must be evaluated and approved by the Planning Commission.

Maximum and Minimum Sizes

ADUs must fulfill the minimal requirements of the building code for living space. Apartment-style dwelling units (ADUs) must provide permanent living, sleeping, eating, cooking, and sanitary facilities. Generally speaking, the maximum size of an ADU is 1,200 square feet.


Buildings with accessory dwelling units (ADUs) must be at least four feet from the rear and side property lines, provided that all relevant fire-resistant building requirements are adhered to. Front yard setbacks are defined by the base zoning district (see your parcel’s zoning for further information on setbacks). For information on applicable fire safety requirements, contact the Fire Prevention Division. In the case of properties having septic systems, buffer distances from the septic areas and needed septic reserve areas will be required.

The Fire Code may also impose extra setbacks from property borders or between buildings, depending on the situation.

Minimum Lot Size

There is no minimum lot size requirement for the construction of an ADU.

Septic System Suitability

An ADU permit may only be provided in places where public sewer service is not available, and the capacity to dispose of wastewater on site is an important aspect in assessing whether a permit can be issued for an ADU. It is recommended that property owners evaluate the septic capacity of their site and/or the capacity of their current septic system before proceeding with design ideas. The building of an ADUrepresents a new use for the land, and the septic system for the unit must be in compliance with current requirements.

Water Availability and Water-Scarce Areas

A crucial consideration in deciding whether a lot can support an ADU in places where public water supply is not accessible is the availability of adequate well water on the property. Parcels located in locations with limited groundwater supply (sometimes known as “water-scarce areas”) are subject to extra regulations.

Local groundwater availability regions are listed on the Sonoma County Groundwater Availability Map and the County’s Zoning and Land Use GIS Viewer, and the Groundwater Availability Area classification of each property may be discovered in the parcel search function of the county’s parcel search.

Well Yield Test

A crucial consideration in assessing whether a lot can support an ADU in places where public water supply is not readily available is the availability of adequate well water. In places where groundwater supply is poor (“water-scarce areas”), parcels are subject to extra regulations. A map of groundwater availability in Sonoma County, as well as the county’s Zoning and Land Use GIS Viewer, identify water-scarce regions, and the categorization of each property’s Groundwater Availability Area may be found in the parcel search.

Zero Net Use Requirements

It is necessary for the applicant to show compliance with Permit Sonoma Policy and Procedure 8-2-2 Guidelines for Net Zero Groundwater Use if the well is located in either a Class 4 Groundwater Availability Area or a Critical Habitat Area.

Before Applying for Permits

In most cases, multiple licenses are necessary in order to create an ADU. The most often issued permits are those for sanitation, water, and construction. Several issues for each permit category are discussed in further detail below.

Step 1: Sanitation

Before submitting an application for a building permit, check to see if there are any additional requirements for wastewater disposal.

  • Does your present septic system have enough capacity to accommodate the additional unit, or are you planning a “bedroom swap” to make way for it? Inquire with a consultant to assess the capacity and quality of your present system, write a findings report, or prepare an application for a bedroom swap. Will you be required to construct a newseptic system? Engage the services of a consultant to provide expert assistance with the design and application for a new system. Do you have access to sewage service? Ascertain that your sewer provider will supply service to the new unit, and get expert assistance in submitting an application for a sewer permit if one is necessary.

It is necessary to get sewage or septic permits before applying for a construction permit for the ADU. These permits should be filed and in the “Issued” state before applying for the building permit for the ADU.

Step 2: Water

  • Determine whether there are any additional requirements linked to water supply before submitting an application for a construction permit. The amount of water required varies depending on the kind of water service and the area. Will the ADU be served by a well in a water-stressed area (as previously mentioned)? To have a dry weather well test performed (which should be done between July 15 and October 1), you should contact a professional who will demonstrate that the well fulfills the minimum water yield criteria set out in the County’s Dry Weather Well Testing rules. The Groundwater Availability Area categorization for your parcel may be seen in the parcel report. The applicant must demonstrate compliance with Permit Sonoma Policy and Procedure 8-2-2 Guidelines for Net Zero Groundwater Use if the well is located in a Class 4 Groundwater Availability Area or a Critical Habitat Area, and the applicant must demonstrate compliance with the State of California’s Groundwater Availability Areas Classification System. Do you require a new well? For assistance in preparing an application for a new well, consult with a specialist. Do you have access to municipal water? Inquire with your service provider to confirm that they will supply service to the ADU.

Prior to filing for an ADU building permit, make sure that all well permits have been received and are in the “Issued” state. Prior to filing for a construction permit, well yield studies should be undertaken and submitted to the WellSeptic Division for consideration.

Step 3: Building Permit

A building permit is necessary for newly constructed ADUs at a bare minimum; however, depending on the complexity of the work, additional permits such as a site study, grading permission, and/or encroachment permit may be required. Fill out an online application for a building permit.

How to Apply for Permits

The majority of permit applications are filed and processed through the use of electronic means. Visit our online permitting website to begin and submit a building permit or other development permit application, pay fees, schedule an inspection, and other services and information. Please check the minimum submission criteria for residential building permits and make sure you have everything you need. With the building permit application, all property owners must sign and submit the Accessory Dwelling Unit Rules and Performance Standards, which are available online.


The size of your ADU is one of numerous elements that affect the amount of money you will have to spend on building permits for an ADU. ADUs may be subject to the following fees in addition to any applicable construction permit or other permit processing costs.

  • Impact Fees are a type of tax. ADUs with a total floor area of less than 750 square feet are free from park and traffic impact fees. It is necessary to pay impact fees on ADUs that are larger than 750 square feet since they are levied in proportion to the square footage of the principal housing unit. Fees for attending school. ADUs with a floor area more than 500 square feet may be liable to school fees if they are located inside a school district. a For further information, speak with your local school district. Fees for water and sewer connections. The following types of ADUs will not be needed to get a new or separate utility connection, as well as any associated connection cost or capacity charge:
  • Junior Ancillary Dwelling Units
  • Internal conversions of existing space within a principal dwelling or an accessory construction
  • Junior Accessory Dwelling Units

More Information

If you have any questions, you should contact the Permit Sonoma department directly. Contact information for the division may be found here.

Other Resources

The Napa Sonoma ADU Center is a non-profit organization that aids homeowners with the ADU planning process in the counties of Napa and Sonoma.

It is located in Napa, California. There are informative webinars, individualized feasibility consultations, a home match program, and other services available through the center.

Contact Information

Make contact with Planning by phone. The working week is Monday through Friday. 10:00 a.m. to 2:00 p.m. from 1:00 p.m. to 3:00 p.m.

  • Phone: (707) 565-1900, option 5
  • CARelay Service: (707) 565-1900, option 5

Address2550 Ventura AvenueSanta Rosa, CA 9540338.465074, -122.72370538.465074, -122.723705


Regulations Concerning Accessory Dwelling Units Calculator for the Accessory Dwelling Unit In order to determine the costs, returns, and advantages connected with establishing an ADUADU Rescue Program, the ADU Calculator can be used. Learn more about how you may be eligible for and submit an application for an ADU or JADU enforcement violation extension in this article. Napa Sonoma ADU CenterThe Napa Sonoma ADU Center is a resource for homeowners in Napa and Sonoma counties who are interested in constructing an accessory dwelling unit (ADU).

Sonoma County Housing Authority

If you want to rent out your ADU, you should consider participating in the Housing Authority’s Housing Choice Voucher program and contributing to the answer to the County’s affordable housing issue by doing so.

State ADU Law

On the online site of the California Department of Housing and Community Development, you may learn about the state’s rules and regulations regarding Accessory Dwelling Units. Visit the State’s Web Site

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