How Long Does It Take to Build an Accessory Dwelling Unit (ADU)?


As the demand for affordable and flexible housing options continues to rise, more homeowners are exploring the possibility of building Accessory Dwelling Units (ADUs) on their properties. ADUs, also known as backyard cottages, granny flats, or in-law suites, offer a range of benefits, including additional rental income, multigenerational living, and increased property value. However, one of the most common questions potential ADU builders have is, "How long does it take to construct an ADU?" In this blog, we'll delve into the factors that influence the timeline of building an ADU and provide a general overview of the construction process.

  1. Planning and Design Phase: The first step in building an ADU is the planning and design phase. This is where you work with an architect or a design professional to develop the layout and design of the unit, taking into account your needs, local zoning regulations, and budget. The duration of this phase depends on various factors, such as the complexity of the design, the speed of decision-making, and the workload of the design professional. Typically, this phase can take anywhere from a few weeks to several months.
  2. Permitting Process: Obtaining the necessary permits is a critical part of building an ADU. The permitting process can vary significantly depending on your location and local regulations. Some areas have streamlined processes for ADUs, while others might have more complex requirements. On average, the permitting process can take around 4 to 8 weeks, but it's essential to research your local jurisdiction's timelines and requirements to avoid delays.
  3. Site Preparation and Foundation: Once you have the necessary permits, the construction process can begin. The first stage involves preparing the site and laying the foundation for the ADU. This phase typically takes a few weeks, depending on factors like the condition of the land and weather conditions.
  • Building the Structure: The duration of this phase depends on the size and complexity of the ADU. For prefab or modular ADUs, construction can be completed off-site, reducing the on-site building time. Traditional stick-built ADUs might take a bit longer. On average, this phase can take anywhere from 3 to 6 months.
  1. Utilities and Interior: With the structure in place, the next step involves connecting utilities such as plumbing, electrical, and heating to the ADU. Simultaneously, interior work, including insulation, drywall, flooring, and fixtures, is carried out. The timeline for this phase can range from 2 to 4 months, depending on the scope of work and availability of contractors.
  2. Inspection and Final Touches: Before your ADU is ready for occupancy, it must pass inspection to ensure compliance with building codes and safety standards. The inspection process can take a few weeks, and any necessary corrections might add to the timeline. Once the inspection is cleared, the final touches are added to the ADU, and it is prepared for occupancy.

The timeline for building an Accessory Dwelling Unit (ADU) can vary depending on several factors, including the design complexity, permitting process, construction method, and availability of contractors. On average, the entire process can take anywhere from 6 to 12 months or more. While it may seem like a lengthy endeavor, the benefits of having an ADU on your property make the time and effort worthwhile. With careful planning, proper research, and professional assistance, you can successfully build an ADU that serves as a valuable addition to your property and your lifestyle.

SKS Construction can assist in plan check, permitting, and even build of your new ADU, making the process a breeze. As an engineering, and construction firm, SKS Construction was established in Los Angeles, California, in 1987.

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