Detailed ADU Scope Checklist – Everything Needed To Build an ADU in Orange County

Accessory Dwelling Units are becoming increasingly popular in Orange County and the neighboring areas. Many homeowners are contemplating the construction of an accessory dwelling unit (ADU; see ADU definition) to suit a range of purposes, such as accommodating aging parents or generating rental revenue to help pay their mortgage.

Designing an ADU or garage conversion is not an easy task, therefore it’s important to have as much knowledge and preparation as possible regarding the requirements of such a project in form of an ADU scope checklist.

Related: Top 50 Frequently Asked ADU Questions

We’re GreatBuildz, a free service that connects homeowners in Los Angeles, Orange County, Ventura & San Diego with reliable general contractors.


We help people every day with the details, scope, and costs that go into accessory dwelling unit and garage conversion projects – below is an overview of all the items required when building an ADU.

How do I begin designing an ADU?

designing adu

When a homeowner is ready to begin the process of constructing an accessory dwelling unit, he or she should seek out an architect or a general contractor.

It’s a good idea to consult with an architect to get an understanding of the costs associated with generating ADU designs and to ensure that your project goals are reasonable in light of local building codes. Generally, misunderstanding local restrictions are the first and most expensive building error. ADU requirements vary widely; seek an expert prior to construction.

Permits, plans, and expert guidance from an architect may appear costly, but they are well worth the cost. Having an illegal ADU on your property might make it harder to refinance or sell your home, so ensure that your project conforms with local ADU standards. It is also beneficial to speak with a general contractor to have a better understanding of the ADU project’s process, prices, expectations, etc.

Before meeting with general contractors, you should be as prepared as possible with a list of the project’s needs and specifications. You will likely meet with numerous contractors to get bids for your project, so you must ensure that each pro is bidding on the same scope of work. The ADU project checklist below is an excellent starting point.

You must ensure that your contractors present you with an estimate that includes all of the precise details you desire for your additional living unit. Start the ADU planning process by reading this ADU scope checklist; remove any items you think are superfluous and include any project-specific remarks. Finally, distribute this checklist to each general contractor that plans to submit a bid for your project. This increases the likelihood of receiving accurate estimates that are comparable.

ADU building is a significant investment and is not inexpensive. Estimates of ADUs may vary considerably dependent on variables such as size, location, laws, etc. Regardless of the specifics of your project, your contractor should provide you with a reasonable ADU estimate.

A reasonable rule of thumb is to gather three to five bids from several ADU contractors before making a final selection. If all of the quotes are similar in price, it suggests that your project is “clear” to each contractor and that their pricing is most likely in accordance with the market.

planning adu

However, inconsistent ADU estimates could imply that something is awry. Maybe the criteria for your project are unclear, or some of your contractors’ bids are excessively high or cheap. In this case, collecting further quotes can help you identify the proper cost of the project.

Keep in mind that a contractor may only provide an approximate, preliminary quote based on your Orange County ADU scope or preliminary plan. You will not receive a precise, thorough cost estimate until you have a complete set of building blueprints. These drawings must be submitted to the city in order to obtain a construction permit and give the contractor the precise details required for a thorough quote.

Building an ADU – Scope Checklist

Detailed ADU Scope Checklist - Everything Needed To Build an ADU in Orange County 1Typical Scope Checklist For Building An ADU – Contact Us For an Editable Version!

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Let’s categorize this ADU scope checklist into each component:



Each accessory dwelling unit and garage conversion must have a sewage line, water line, electricity connection, and gas connection (unless your ADU is all electric). It is possible that these services will be linked in several locations around your home, necessitating multiple trenches/digs. This will be evident to your contractor, and their bid should reflect this.

You should be aware, however, that the cost of installing utilities can vary greatly depending on whether these lines can be run (trenched) through the earth or must be put under existing concrete sections, which would need the removal and replacement of the concrete.

Rough Construction

rough construction

This includes the majority of the structure of the ADU and consists of several distinct elements, therefore it is essential to guarantee that the contractor’s estimate includes every item you anticipate. In addition, it is common for the contractor to furnish the majority, if not all, of the supplies in this section (and included in their bid). Make certain to clarify this with your ADU contractor.

The majority of the details in this section should be included in your ADU plans and be evident in your proposal. Nonetheless, there are several items in this segment that are frequently overlooked… hence, please analyze bids carefully to assure their inclusion. Often overlooked things include the water heater, closet doors, recessed lighting, gutters/downspouts, HVAC, baseboards and casing, and, if needed, any roof rainwater collecting system.

Some materials in this category of ADU construction can be chosen by the contractor without involvement from the homeowner…materials such as concrete, wood, drywall, etc. Yet, there are other aspects in which the homeowner may and should have input; otherwise, the contractor will choose the lowest quality available materials. Such examples include roofing material, windows, doors, lighting, flooring, HVAC system, and water heater (ie. tankless).

Hence, be explicit with your contractor about the materials you want to choose; this will enable your contractor to produce a more accurate cost estimate.


modern adu kitchen

Cabinets, countertops, and appliances are obvious components of an ADU kitchen, making it quite straightforward. Nonetheless, kitchen design planning is essential. Some ADU plans have a kitchen layout, while others do not. You must ensure that your contractor is aware of your precise requirements.

Make sure you:

  • 1) offer feedback on the desired style/materials, particularly for the cabinets and countertops
  • 2) determine the exact layout and measurements

You should begin space planning by choosing your appliances. Because an ADU kitchen is likely to be tiny, you should choose small equipment, such as a narrow refrigerator, stove, hood, microwave, dishwasher, and sink. Based on the measurements of your appliances, the size of the cabinets will be determined. Consider installing a microwave/hood combination just over the stove for efficiency. If you have the room, a small island may serve as both counter space and a kitchen table/bar.

Examine each bid carefully to determine which kitchen items are included. Cabinets are probably included. Countertops and backsplash are either included in the estimate or an ‘allowance’ (or maximum cost) for this material is included. Hence, if you choose a more expensive type of countertop, you will be responsible for the price difference. Often excluded from bids are appliances, sinks, faucets, cabinet knobs, etc. “Installing appliances” is a common omission, so if you want your contractor to perform this task, include it in your estimate.


modern adu bathroom

When constructing an ADU, the bathroom is slightly more complex than the kitchen and needs more homeowner thought and decision-making. The majority of components in the bathroom, such as the floor/shower tile, vanity, mirror, faucet, shower hardware, and even the toilet and tub, will require you to pick the specific material you want to use (unless you just let the contractor decide).

Due to the homeowner’s need to make several material decisions for the bathroom, the cost of this portion of the ADU might vary greatly. This will be bid differently by each contractor; thus, it is essential to examine each proposal for inclusions and exclusions. Some contractors will specify that the homeowner will “supply” (i.e., directly pay for) the faucet, vanity, tub, tile, toilet, etc. Some proposals will include the expense of them as an allowance.

Moreover, some bids will include some of these goods while excluding others. It is uncommon to find consistency across these things in contractor bids; thus, it is crucial to evaluate and compare each proposal.

In the bathroom, the glass shower door, exhaust fan, and recessed lighting or sconces are frequently omitted, so if you expect them, make sure they are included. Specify with your contractor if you want a tub/shower or a walk-in shower. If you choose a walk-in shower, let your contractor know whether you want tile or a shower pan on the floor.

ADU scope checklist

Frequently, ADU designs just depict the structure itself, and we forget to include any elements that may be required outside the structure. Whether you’re creating an ADU to rent out or for your own family, you’ll certainly want to create a pleasant interior and exterior atmosphere. Hence, if you believe that you will require a fence, patio concrete, a walkway to the unit, landscaping, etc., ensure that the contractor is aware of this and includes these in their estimate.

Fixtures and Fittings


These are elements that are present throughout the ADU, and the homeowner must choose the materials for each one. They include flooring materials, light fixtures, doorknobs, and so on. It is essential to thoroughly examine each bid to establish whether or not these materials are included. Typically, contractors do NOT include these supplies in their quoted price and expect the homeowner to pay for them separately.

The selection of the numerous materials necessary to construct an ADU can take a homeowner a considerable amount of time and may include frequent online and in-store shopping. If you want to pick materials on your own, try your best to do it as early in the process as feasible. a contractor or designer/architect can offer guidance on material selection. Material delays are a typical cause of ADU projects taking longer to finish than necessary.

How can I compare a prefabricated ADU to a conventional ADU?

A prefabricated ADU is constructed at a factory, transported to the construction site, and installed there. A firm that sells prefabricated or modular ADUs should be able to detail exactly what is included in and on the ADUs they are selling. This can make the client’s life easier if they choose a conventional design/model, but does not permit a bespoke ADU size, plan, or layout. With a prefabricated ADU, your responsibilities (and additional costs) will be limited to the site work required to accommodate the ADU, such as the foundation, utility connections, landscaping/hardscaping, and fencing.

If you are considering building an ADU, I hope this ADU checklist will serve as an excellent starting point. After reviewing this list and deciding which components to incorporate into your ADU project, you will be well on your way. It might be wise to print multiple copies of this checklist and hand one to each contractor you meet. So, you will have greater control over maintaining the consistency of each proposal. Each contractor has their own process for putting together a bid, so it is probable that you will need to examine each thoroughly, especially in terms of whether components are included or excluded in each proposal.

GreatBuildz is a free service that connects homeowners in Los Angeles, Orange County, Ventura & San Diego with reliable, thoroughly screened general contractors and provides project support from start to finish.


Submit your project to be connected with several fully vetted, trustworthy contractors who are experienced with ADUs. For more info, visit or call 818.317.3567 today.

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