Attached ADU Cost Calculator for Reno

The figures published on this site put a small attached unit under 500 square feet at $100,000 to $180,000, a one-bedroom of 500 to 750 square feet at $150,000 to $270,000, and a larger unit of 750 square feet and up at $220,000 to $380,000 and beyond. The home page also gives an overall attached range of $150,000 to $300,000. This calculator works from your specific tie-in, systems and ground rather than an average, and tells you which tier the result lands in.

Almost always, at the same size and specification. You save an exterior wall, most of the trench and part of the foundation. The published tables on this site show the same thing — attached tiers sit roughly 15 to 20 percent below the detached equivalents. What attached costs you is flexibility: the unit has to go where the house allows, its windows face where the existing walls face, and any future work on the shared wall involves both dwellings.

Yes, and from 1 July 2026 Nevada's AB 396 prevents local ordinances in Washoe County, Reno and Sparks from prohibiting long-term rental of an ADU. What makes it work in practice is separation: its own entrance, its own meters, and ideally its own water heater and heating, so a tenant is not sharing a thermostat with your family. That separation is a real cost and it is priced separately in this calculator, because whether you need it depends entirely on who is moving in.

Converting existing enclosed space — an oversized bonus room, an enclosed sunroom, a basement area — is the cheapest form of attached ADU, because the shell exists. Independent 2026 figures put interior conversions at roughly $150 to $300 per square foot against $300 to $575 and up for detached new build. The constraints are the ones you inherit: ceiling height, window and egress provision, and whether the space can be separated with its own entrance without ruining the house's own circulation.

For it to function as a separate dwelling, yes — and building departments will expect one. That entrance also has to be reachable without walking through your house or your private yard, which on a narrow lot is a genuine design constraint rather than a formality. It is worth resolving on paper early, because it often decides which side of the house the unit can go on, and therefore what it costs to connect.

Expect a fire-rated separation between the two dwellings as a code requirement, and treat sound as a separate question on top of it. A fire assembly is not automatically a quiet one, and the difference between the two is decoupling and mass — resilient channel, a second layer of board, insulation in the cavity. It is inexpensive while the wall is open and expensive afterwards. If a tenant is moving in rather than family, specify it deliberately rather than hoping.