How Long Does It Take To Build a Detached ADU?

Adding a detached accessory dwelling unit (ADU) to your property is a great way to gain extra living space, rental income, or flexibility for multi-generational living. Many homeowners ask the same thing before getting started: how long does it take to build a detached ADU?

Most projects fall within a range. If you’re planning to build from the ground up, this guide will walk you through what to expect during each phase of a project.

Planning and Permitting

Before breaking ground, you’ll spend time in the planning and permitting phase. Depending on the location and project scope, this may stretch from several weeks to a couple of months.

Homeowners deciding which is best between attached and detached ADUs should consider the timeline and complexity of construction. While detached units offer more privacy and flexibility, they typically take longer to build and require additional steps, including utility hookups and meeting different zoning requirements than attached units.

For example, some areas in Lexington, Kentucky allow detached builds more easily than others. Always check with the local permitting office early to avoid delays.

Construction Timeline

Once the permits are approved and plans are finalized, building can begin. On average, a detached ADU takes four to nine months to construct. This timeline can be shorter with prefab units or longer for custom builds.

The process involves several stages: site preparation, foundation, framing, roofing, and interior systems, including plumbing and electrical. Prepping the site and laying the foundation can take two to four weeks, depending on the weather and soil conditions. Framing and roofing might take another month, followed by several weeks of interior work.

Each phase depends on the one before it, so delays in one area—material shortages or labor gaps—can ripple through the rest. That’s why it’s smart to work with professionals who communicate clearly and often. The more prepared the builder is, the smoother the process will be.

Design Details That Affect Timing

If you’re going with high-end materials, custom cabinetry, or energy-efficient upgrades, expect the build to take longer than if you were using average materials. These upgrades add two to four weeks to the construction timeline, depending on availability and complexity.

For example, waiting on specialty windows or installing solar-ready infrastructure could push your project back. Sticking to simple finishes and open layouts, though, expedites the process.

How Long Does It Really Take?

How long does it take to build a detached ADU? Most detached ADU projects wrap up within 6–15 months, though that timeline isn’t set in stone. A realistic timeline includes permitting, planning, and construction, with some wiggle room built in for unexpected surprises.

Not to mention, the project will also need to pass final inspections before it’s move-in ready. This process typically takes one to four weeks, depending on your city’s schedule and the speed at which you make required adjustments. If you’re ready to get started, talk to local builders, research your city’s zoning requirements, and map out your goals.

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