ADU Guide

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Introduction to ADUs

Whether you're planning to increase your property value, generate extra income, or accommodate your family members, this page is an excellent resource to start with if you're contemplating building an ADU in Irwindale. We have all the information you need to learn about the advantages of ADUs.

What's an ADU?

ADUs can be referred to by several names, such as accessory dwelling units, granny flats, in-law units, second units, and casitas. Regardless of what term you use, ADUs are fully independent homes designed to accommodate at least one person and are situated on the same lot as a primary residence. ADUs include living and sleeping quarters, a kitchen, and usually a private bathroom.
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Benefits of ADUs

Rental Income

The rental income you can generate from your ADU may fluctuate based on factors such as the ADU's dimensions, its location, and the amenities it offers.

Increase in property Value

Constructing an ADU can have a positive impact on your property's value. As a general rule of thumb, your property's value may increase by approximately 100 times the monthly rental rate of your ADU. For instance, if you can generate a rental income of $1,000 per month from your ADU, your property's value could increase by around $100,000.


ADUs can serve a variety of purposes, including accommodating guests or family members, serving as a home office, or providing rental income.


ADUs can be designed to be environmentally friendly, utilizing sustainable materials and energy-efficient systems to reduce your carbon footprint.

ADU Regulations in Irwindale

Allowed locations

In most cases, having an ADU on your property is possible if the land is zoned for residential use, with some exceptions. Additionally, there must be an existing or planned single-family home on the property, or an already established multi-family building (such as a duplex, triplex, or apartment/condominium complex).

Minimum lot size

Fortunately, there are no minimum lot size restrictions for building an ADU, meaning that properties of any size can be eligible. If you own a single-family home, you can typically build up to one or two ADUs on your property. The number of ADUs permitted on multi-family properties varies depending on the type of ADU built and the number of existing dwelling units on the property.

Maximum square footage

The maximum size of your ADU is determined by the type of unit you intend to build. For instance, the maximum size of a detached ADU on your property may differ from that of an attached ADU.

Maximum height

It is typically possible to build an ADU that is at least one-story and 16 feet tall.


In general, conversion ADUs and junior ADUs do not necessitate any parking. Attached and detached ADUs, however, usually require at least one parking space, unless your project qualifies for an exemption from parking requirements.

So much opportunity in such a small space.

Guest House

Host guests in style with a backyard ADU. Enjoy privacy and comfort in your own space.

Rental Income

Generate passive income with a backyard ADU. Rent it out long-term or as a vacation rental.

Home Office

Increase productivity and work-life balance with a backyard ADU. Enjoy a quiet, dedicated workspace.


Indulge in hobbies and passions with a backyard ADU. Create a custom space for leisure activities.

Elegant Design
Predictable Timeline
Upfront Pricing

Reserve any of our Shift Models before April 30th and receive a free Sonos sound package!


Model 1

from $168,000Studio480 SF

Model 2

from $224,0001 Bed 1 Bath640 SF

Model 3

from $424,0002 Bed 1 Bath1280 SF

Model 5

from $336,0002 Bed 2 Bath960 SF


from $195,0001 Bed 1 Bath490 SF

Shift +

from $295,0001 Bed 1 Bath540 SF

Shift Live

from $109,900Studio285 SF

Shift Play

from $85,900Studio220 SF

Irwindale ADU FAQs

How long does it take to get an ADU in Irwindale?

The timeline for getting an ADU (Accessory Dwelling Unit) in California can vary depending on a number of factors, including local zoning regulations, permitting requirements, and the complexity of the construction process. However, here are some general estimates for each step of the process:

  1. Design and Planning: This phase can take anywhere from a few weeks to several months, depending on how long it takes to finalize your ADU design and obtain any necessary permits.
  2. Permitting and Approvals: The permitting process can take several weeks to several months, depending on the local jurisdiction and the complexity of the project. Some jurisdictions offer expedited permitting for ADUs to encourage their construction.
  3. Construction: The construction phase can take several months to a year, depending on the size and complexity of the ADU and the availability of materials and labor.
  4. Final Inspection and Occupancy: Once construction is complete, a final inspection will need to be conducted to ensure that the ADU meets local building codes and safety requirements. Once the ADU passes inspection, it can be occupied.

Overall, the timeline for getting an ADU in California can range from several months to over a year, depending on the specific circumstances of your project.

What are the common types of construction available for ADUs?
  • Site Built Construction
    - Pros - Unlimited customization options (easy to match existing home)
    - Cons - takes longer, change orders are common
  • Pre-fab Modular Construction (Volumetric) - This is Steelblox
    Pros - Saves time, engineered for efficiency, finished in factory
    - Cons - transportation and setting costs, less design options
  • Pre-fab Modular Construction (Panelized)
    - Pros - reduced transportation costs, engineered for efficiency
    - Cons - more sitework, limited configurations
Are there design restrictions on ADU’s in Irwindale?

Yes, there are some design restrictions on ADUs (Accessory Dwelling Units) in California. The state has established some general guidelines for ADU design, and local jurisdictions may also have their own specific requirements and regulations. The 2 we find to be the most important to consider when submitting application to build:

  • Access and egress: ADUs must have a separate entrance and exit from the primary dwelling unit, and must meet local fire safety requirements.
  • Design compatibility: ADUs must be designed to be compatible with the architectural style of the primary dwelling unit and surrounding neighborhood. Some local jurisdictions may require that ADUs be designed to match the primary dwelling unit in terms of materials, colors, and roof pitch.

To help mitigate the latter, many municipalities have adopted “Pre-approved Design” programs, that allow companies like Steelblox that sell ADUs to submit designs that are reviewed and approved in advance and made available to owners wishing to add ADUs to their properties. This program saves a significant amount of time and money for the applicants.

How are modular homes classified in Irwindale, and who is responsible for making sure they are built properly?

Modular homes are classified as “Factory-Built Housing” in CA. Factory-built housing (FBH) is a residential building or dwelling unit that is manufactured off-site and regulated by the California Department of Housing and Community Development (HCD). These housing units are approved and inspected on behalf of HCD by HCD-approved agencies and will bear an HCD “insignia of approval” upon completion. FBH typically refers to modular housing built and transported as one or more modular units and set on a permanent foundation.

Factory-built housing offers many advantages when compared to traditional site-built construction including: beautiful and thoughtful designs, a streamlined permitting process, accelerated project timelines, lower raw material waste, and a higher quality finished product. The manufacturing process allows for tighter quality standards to be monitored during the construction process as well. This method of construction may alleviate many of the pains felt by homeowners and their neighbors during traditional construction projects.

Is a Modular or Factory Built Home the same as a Manufactured Home?

Manufactured homes are also built off-site and delivered near completion but these are built to the Manufactured Home Construction Safety Standards (MHCSS) established by the Federal Department of Housing and Urban Development. These may be permanently installed on foundations or they may be mounted on frames with wheels for mobility. Mobile Homes and Tiny Homes are typically constructed to the HUD standard, and are not considered the same when it comes to property values and financing options.

Chattel loans are commonly used to finance the purchase of mobile homes, which are considered personal property rather than real property if they are not permanently affixed to a foundation. Mobile homes can be more difficult to finance than traditional homes due to their status as personal property, and chattel loans can be a viable financing option for mobile home buyers.

Because chattel loans are secured only by the personal property being financed, they generally have higher interest rates and shorter repayment terms than traditional mortgage loans. Additionally, because personal property can be more difficult to value and sell than real property, lenders may require a larger down payment or higher credit score to qualify for a chattel loan.

It's worth noting that in some cases, homeowners may also use a chattel loan to finance the purchase of an accessory dwelling unit (ADU) that is designed to be movable or modular. However, the availability and terms of chattel loans for ADUs can vary depending on the lender and the specific circumstances of the ADU project.

Is getting a modular ADU faster than traditional site-built construction?

Yes, getting a modular ADU (Accessory Dwelling Unit) is generally faster than traditional site-built construction for several reasons.

First, modular construction takes place off-site in a factory-controlled environment, where the construction process can be streamlined and optimized for efficiency. This means that the building process can occur simultaneously with site preparation, which can shorten the overall timeline for the project.

Second, modular construction relies on prefabricated modules that are transported to the building site for final assembly, which can further reduce construction time. Once the modules are delivered to the site, final assembly and installation can take just a few days.

Third, modular construction is not subject to weather delays or other on-site complications that can arise during traditional site-built construction. Because the modules are constructed in a controlled factory environment, the building process is not as vulnerable to factors such as rain, wind, or labor shortages.

Overall, the faster construction time of modular ADUs makes them an attractive option for homeowners who are looking to add living space to their property quickly and efficiently. However, it's important to note that the timeline for getting a modular ADU can still vary depending on factors such as permitting requirements, design complexity, and the availability of materials and labor.

Are modular ADUs less expensive than Site Built ADUs?

Typically not. Usually the savings picked up by the efficiencies of repetitive production, are offset by the cost of transportation and setting of the modules. In general, modular builders tend to design their models to be priced at a competitive rate in the markets they service. As with any type of construction, the building materials and finishes play the largest role in setting the price.

How disruptive is the modular ADU installation process?

The disruptive nature of the modular ADU (Accessory Dwelling Unit) installation process can vary depending on several factors, including the size of the ADU, the site conditions, and the specific installation process used.

Overall, the installation of a modular ADU can be less disruptive than traditional site-built construction because much of the construction process takes place off-site in a factory-controlled environment. This means that there is typically less on-site construction activity and fewer workers present at the building site during the installation process.

Additionally, the modular ADU installation process is typically faster than traditional construction, which means that any disruption to the site is minimized. Once the pre-fabricated modules are delivered to the site, installation and assembly can typically be completed in a matter of weeks, which can reduce the overall disruption to the homeowner and the surrounding community.

What are the typical options used to pay for an ADU?

There are several financing options available to pay for an ADU (Accessory Dwelling Unit), including:

Cash: Paying for an ADU with cash is the simplest option, but it may not be feasible for all homeowners.

Home Equity Loan: A home equity loan allows homeowners to borrow against the equity in their home to fund the construction of an ADU.

Home Equity Line of Credit (HELOC): Similar to a home equity loan, a HELOC allows homeowners to borrow against the equity in their home, but with more flexibility to borrow as needed.

Personal Loan: A personal loan can be used to fund the construction of an ADU, but typically has higher interest rates and shorter repayment terms than other financing options.

Construction Loan: A construction loan is a short-term loan that can be used to fund the construction of an ADU, with the loan being paid off once the construction is complete, this option is only available when combined with new construction of the main house..

Refinancing: Homeowners can refinance their existing mortgage to free up cash to pay for an ADU, or to take advantage of lower interest rates.

Government Programs: Some local governments offer financing programs or incentives to encourage the construction of ADUs, such as low-interest loans or tax credits.

Do all ADUs require a building permit in Irwindale?

There are primarily 3 types of Accessory Structures that are added to a primary residence:

  • Accessory Sheds 
    - Less than 120 sq ft - No permit required (no temp control, or waste lines)
    - Greater than 120 sq ft - Permit required
  • Accessory Dwelling Units - Permit required
    - CA Statewide Exemption - 800 sq ft or less, 16 ft height or less 
    - CA Partial Exemption - 801-1200 sq ft - Max 2 bed 2 bath
  • Jr Accessory Dwelling Units (AKA Conversion ADU’s) - Permit required
    - Conversion of attached space such as a garage or basement up to 500 sq ft.
How many ADUs can be added to an owner's property?

The number of ADUs allowed on a property depends on the type of ADU and what's already on the property.

For the most part, a single-family property is allowed 1 ADU. The exception is that a single-family property can have 1 Junior ADU (JADU) and 1 Detached ADU (if the Detached ADU is no more than 800 sq. ft.)

Generally, 2 Detached ADUs are allowed on a property with an apartment or condo building. The number of Conversion ADUs allowed depends on how many apartments or condos are already on the property; the number of allowed Conversion ADUs is 25% of that number (except at least 1 Conversion ADU will be allowed).

What California laws guarantee the right to add an ADU in Irwindale?

The California state law that guarantees the right to add an ADU (Accessory Dwelling Unit) to your home is Senate Bill 1069 (SB 1069), which was signed into law in September 2016. SB 1069, along with Assembly Bill 2299 and Senate Bill 13, collectively make up the California Accessory Dwelling Unit laws.

SB 1069 is designed to promote the development of ADUs by streamlining the permitting and approval process and reducing some of the fees and requirements associated with ADU construction. The law establishes several key provisions, including:

  • Zoning requirements: Local jurisdictions are required to allow ADUs in all single-family and multifamily residential zones, subject to certain size and location requirements.
  • Permitting process: Local jurisdictions are required to process ADU permits within a specified timeframe and may not impose certain fees and requirements, such as parking or utility connection fees.
  • Owner-occupancy: Local jurisdictions may not require that the property owner occupy either the primary or accessory dwelling unit.
  • Building standards: ADUs must comply with building codes and safety standards, but may be subject to certain relaxed requirements, such as off-street parking and utility connections.

Assembly Bill 2299 (AB 2299) and Senate Bill 13 (SB 13) are two companion bills that were signed into law in September 2016, along with Senate Bill 1069 (SB 1069). Together, these three bills make up the California Accessory Dwelling Unit laws and have significantly modified the regulations for ADUs in California. Here are some of the key changes made by AB 2299 and SB 13:

  • Local jurisdiction requirements: Local jurisdictions are required to update their zoning ordinances to comply with the new ADU laws, and to submit their compliance with the state housing department.
  • Permitting process: Local jurisdictions are required to approve or deny ADU permit applications within 60 days, with certain exceptions for more complex projects. If the jurisdiction fails to take action within 60 days, the application is deemed approved.
  • Fees: Local jurisdictions may only charge fees that are directly related to the ADU construction and must provide a fee schedule to the public. Additionally, jurisdictions are required to waive certain fees for ADUs under 750 square feet.
  • Parking requirements: Local jurisdictions may not require additional off-street parking for ADUs if they are located within one-half mile of public transit or within an architecturally and historically significant district.
  • Utility connections: Local jurisdictions may not require homeowners to upgrade their utility connections to accommodate an ADU, unless they also require this of all new construction in the area.

Overall, AB 2299 and SB 13 were designed to further streamline the ADU permitting and approval process, reduce costs and fees for homeowners, and increase the availability of affordable housing in California.

What is SB9 and how does it impact what I’m allowed to build on my property?

SB9 can be a bit confusing when applying it to the previous laws created specifically for ADUs. The core of the law is to allow landowners/homeowners to split a parcel into 2 parcels, thus creating 2 separate lots. The law further states the owner may have 2 living structures on each. The review and approval process to do this is now a “ministerial review”...which essentially means building department officials can review the applications in a “checklist” type of review, without applying opinions as to whether the property qualifies or not. 

As an example if you own a home a 1 acre lot with a single family residence already built, you can:

  1. Split the lot into 2 parcels
  2. Add an ADU to the lot with the SFR
  3. Build a 2nd Single Family Residence on the newly created lot
  4. Add an ADU on the newly created lot

Thus increasing the number of dwellings on the 2 lots to a total of 4.

One key restriction of SB9 is the owner must occupy 1 of the 4 dwellings as its primary residence. There are lots of developing local ordinance around this mandate, especially in more established communities where property values could be significantly impacted. STAY TUNED!!!

Can I use my ADU as a Short term rental in Irwindale?

State law notes that ADU’s are intended to be rented as long-term housing with average rental timelines exceeding 30 days. That said, local jurisdictions may allow you to rent your ADU for shorter time frames (Airbnb’s or VRBO’s as example).

Is Solar required for new ADUs in Irwindale?

In California, new construction of residential buildings, including ADUs (Accessory Dwelling Units), is required to comply with the state's solar mandate, which requires that all new residential buildings be constructed with solar panels or other renewable energy sources.

The solar mandate was established by the California Energy Commission (CEC) in 2018 and applies to all new residential buildings that receive a building permit on or after January 1, 2020. The mandate requires that all new residential buildings, including ADUs, be designed and built to produce enough solar energy to offset the building's annual electricity usage.

However, there are some exceptions to the solar mandate for ADUs. Specifically, ADUs that are less than 800 square feet in size, or that are constructed on a lot that is shaded by trees or adjacent buildings, may be exempt from the solar mandate.

It's worth noting that while the solar mandate applies to new residential construction, it does not require homeowners to install solar panels on existing homes or ADUs. However, homeowners may still choose to install solar panels or other renewable energy sources on their existing homes or ADUs as a way to reduce their energy costs and environmental impact.

Are fire sprinklers required to be installed in new ADUs in Irwindale?

In general, fire sprinklers are only required if the primary residence has them installed. There are however some circumstances where Building and Safety can require sprinklers if there is difficult or distant access to fire hydrants.