Nine Things to Know Before Building Your ADU
Getting Started with your ADU
Building an ADU can be complicated. We recommend working with a qualified local Architect who has experience dealing with cities, approvals, and general contractors to help guide you through the process. Having a trusted, reliable team who has been through the process can alleviate many potential headaches and can help get your project off on the right foot.
After designing and building many ADU’s, we’ve put together a list of the key items for owners to understand when starting their ADU project. If you want to get started on your ADU project now, click the button below to set up a consultation with our team.
1. Visit Your City or County for the Local ADU Guidelines
The city where your property is located will typically have a special set of ADU guidelines. It is essential that you or your team understand these requirements prior to selecting or designing your ADU. The key guidelines you are looking for should be setbacks, allowable square footage, height limits, and setbacks away from your primary residence.
If you choose to traverse this process alone, we suggest scheduling a meeting with a planner at your local city to review the requirements.
2. setbacks
Setbacks define the distance that your unit needs to be away from different features on your site. For example, side yard setbacks define a distance that the unit needs to be set away from the side yard property line. We find that most cities have 4-foot setbacks from the rear and side yard property lines.
Another requirement to be aware of is the allowable distance from the primary residence to the ADU. This is technically not a setback. However, it is a similar requirement and, therefore, mentioned in the same category for simplicity's sake. Typically, cities have a minimum distance that your ADU must be from your primary residence. This is usually 10 feet.
If your lot is big enough to locate your desired unit without infringing on these setbacks, you are off to a good start. Some lots may not be able to adhere to these requirements if they are smaller in size. In this case, there are alternative solutions that can be discussed with your architect.
3. maximum floor area
It is essential to know the maximum allowable square footage of ADU units allowed in your area. In many areas, the largest size of ADU you can build is 1,200 SQFT or 1,000 SQFT. Be sure you are designing or selecting a unit that is under this requirement. The floor area should be calculated from the outside face of the exterior wall. Typically, mechanical spaces and outdoor covered patios do not need to be included. However, this can vary depending on the local requirements.
4. Maximum height Limit
Cities will often limit the height of ADUs to prevent you from building a two-story unit. In many areas near us, the limit is 16 feet. It is important to be aware of the height limit and be sure the unit you are selecting or designing is a unit that is permittable.
5. Measure your Site or Get A Survey
Some cities will require a survey to be completed for your property, however many will not. If a survey is not required, you or your architect can usually access the city GIS system to obtain the boundary lines for your property. It is important to note that these lines obtained from the city’s system are not always accurate. In this case, we recommend verifying the boundary lines with your title report. Your architect can help you translate the verbal description of your property lines found in your title report to the actual lines and angles that need to be shown on your ADU site plan.
You can also review the purchase documents from the sale of your home to see if there is a survey attached. Oftentimes a previous owner will have completed a survey.
If any of the documentation is unclear, we recommend having a proper survey completed for your lot. Although the city may not require it for permits, if an issue is discovered during construction where you are not conforming to the proper setbacks, this could result in a much bigger issue.
6. Utilities for your ADU
Understanding the existing utilities on your property and their capacity/adaptability to be able to service the new ADU is critical. The cost of utility upgrades and installation are often significant unforeseen costs if not planned for in advance. We want to be aware of the utility requirements as much as possible to help owners factor these costs into their overall project budget.
7. Electrical Power for Your ADU
Many cities require ADU’s to have a minimum of 100amps dedicated power to the unit. Be sure to check your main panel to see if you can partition this much power off to the ADU. We typically recommend having more power dedicated to the ADU if possible, depending on the use of your unit.
If you do not have adequate electrical power to the unit, you may need to upgrade your main electrical panel. A qualified electrician should be able to help you determine this. We recommend looking at this before building/designing your unit as it can be an added unknown cost not anticipated in your initial project budget.
An idea of the bigger systems desired in the unit, such as appliances, solar panels, and HVAC equipment, is good to know in advance so a moderately accurate estimate of the power requirements for the unit can be made. Again, we recommend having a qualified electrician and architect work to help asses if upgrades/modifications need to be made to your existing system and how much power your ADU needs.
8. Plumbing Requirements for your ADU
You will want to understand how water will be brought from your main water line to your ADU. This usually means knowing what size your main water line is, and its capacity to service an additional unit. Factors such as bathrooms serviced in the main home, line size, other water requirements on your site, and number of bathrooms in the ADU should all be considered when determining if your existing system can support your ADU.
Understanding your sewer is important as early as possible in your process. Many cities will not want the ADU sewer to connect into the existing sewer of the primary residence. In this case you will need to connect in another location and provide a cleanout. This small requirement could trigger additional trenching and sewer lines installation, triggering additional potentially unforeseen costs. Go to the city and ask the Public Works Division what their requirements are for ADU sewer systems.
The same goes for natural gas systems for your ADU. Many homeowners are choosing not to install gas in their units, some for personal/financial reasons, others because cities are strongly discouraging or even restricting new units from using gas. Piping gas to your unit should be decided upon early in the process. If no gas will be piped to your unit, induction cooktops, electrical washer/dryers, water heaters, HVAC equipment and all other appliances need to be specified as electrical only.
Again get a consultation by your architect and a qualified plumber/general contractor prior to starting your unit on all items related to plumbing.
9. Plan, Plan, Plan
Invest the time and resources into properly planning and designing your unit. We’ve received countless calls from owners who attempted to “wing” their ADU projects and dug themselves into a hole. Work with a qualified team from the beginning who can help make the process go smoothly and provide guidance during the process. It is important to note that there will always be challenges during a project, however a qualified team will be able to minimize those challenges and come to the table with good solutions when they arise.
If you are interested in building an ADU and would like to get the process started, our team at Rost Architects would be happy to help. You can schedule a consultation at the link below to kick things off.
How does Rost Architects Work?
We have been working in the ADU space since 2017 and have developed a collection of ADU designs that owners can access. Each of these units has been thoughtfully designed and includes features/elements typically used in our luxury homes but translated into smaller-scale ADUs.
We typically start the ADU design process by selecting a unit that works for the owners and then customizing specific features, materials, architectural elements, and layouts to meet unique needs. We’ve found this process is nice for owners because it allows them to obtain a unit that is truly custom for them without the massive upfront design cost of starting from scratch.
We enjoy working with individual owners in this more boutique approach and handle our projects with care and professionalism. Our goal is to deliver a high-quality, aesthetically pleasing, and functional unit for you and your family.
If you would like to see some of our ADU models, click the button below.
