Choosing the right Issaquah ADU builder is the smartest first step toward adding a legal second living space to your property. An accessory dwelling unit can house family, earn rental income, or boost your home value. However, costs and permit rules vary, so it helps to know what to expect before you begin.
ADU pricing depends mostly on the type of unit and its size. Because you are building a complete living space with a kitchen and bath, costs run higher per square foot than a simple addition. Here are typical 2026 ranges:
These are general ranges, not quotes. For an exact price, request a free estimate and we will review your lot and design goals with you.
For many homeowners, yes. An ADU can generate steady rental income month after month. In addition, it often raises resale value and gives you flexible space for aging parents or grown kids. Because Issaquah sits in a high-demand rental market, the added unit frequently pays back a meaningful share of the build cost over time. Therefore, an ADU is worth planning carefully with an experienced builder.
Not every contractor handles ADUs well, so it pays to vet your builder carefully. Look for these signs of a reliable Issaquah ADU builder:
As a licensed general contractor, we manage the whole project — design, permits, foundation, framing, and finish — so you work with one team from start to finish.
There is more than one way to add a unit, so your Issaquah ADU builder should match the design to your property. A detached ADU, often called a DADU, is a separate cottage that offers the most privacy. An attached ADU shares a wall with your main home and usually costs less to build. A conversion turns an existing garage or basement into living space, which is the fastest and most affordable option. Each approach has trade-offs in cost, privacy, and permitting.
Yes. Every ADU requires a building permit from the City of Issaquah Permit Center, along with plan review for zoning and setbacks. A good builder pulls these permits for you and schedules inspections. Recent Washington rules have made ADUs easier to build statewide, so this is a great time to explore your options. For energy-code basics that affect design, the U.S. Department of Energy is a helpful resource.
Most ADUs take four to eight months from design to move-in, depending on the type and complexity. Permitting alone can add one to three months before construction starts, so plan ahead. A conversion moves faster because the shell already exists, while a detached new build takes the longest. Because weather and inspections affect timing, your builder should give you a realistic schedule up front.
How much does an ADU cost in Issaquah?
Most ADUs run $150,000 to $400,000 in 2026, based on type and size. A garage conversion is cheapest; a detached new-build unit costs the most.
Do I need a permit for an ADU?
Yes. Every ADU needs a City of Issaquah building permit plus zoning review. Your builder should handle permitting and inspections for you.
Can I rent out my ADU?
In most cases, yes. Many Issaquah homeowners build an ADU for rental income or to house family. Check current city rules before you plan.
How do I choose a good ADU builder?
Pick a licensed, bonded, and insured contractor with written estimates and local permit experience. Read our remodeling cost guide for more tips on vetting contractors.
Ready to add an ADU? TJ Construction is a licensed, bonded, and insured Issaquah ADU builder serving Issaquah, Sammamish, Bellevue, Redmond, and the greater King County area. We give free, written, no-obligation estimates so you know exactly what your project will cost.
📞 Call or text 206-999-5442 · ✉️ service@tjconstructionwa.com