Detached ADU Cost Calculator for Reno

The figures published on this site put a small detached unit under 500 square feet at $120,000 to $220,000, a one-bedroom of 500 to 750 square feet at $180,000 to $320,000, a larger unit of 750 square feet and up at $250,000 to $450,000 and beyond, and a higher-end custom detached unit at $400,000 and up. Independent 2026 figures for northern Nevada put detached backyard ADUs at roughly $300 to $575 and up per square foot, which brackets the same territory. This calculator works from your specific lot rather than an average.

Reno's ordinance, adopted 8 October 2025, requires a minimum lot size of 5,000 square feet and that the ADU be both smaller and shorter than the main house. A cap of 50 percent of the primary dwelling up to 1,200 square feet is commonly cited, along with a height limit around 16 feet and 5-foot side and rear setbacks, but treat those specific figures as unconfirmed and check them against the current ordinance. Nevada's AB 396 sets no statewide size cap, and from 1 July 2026 it prevents local setbacks stricter than those applying to the primary residence.

Because Washoe County's design ground snow load is set by elevation and it climbs steeply — from about 43 psf on the valley floor to 203 psf at 6,000 feet and 328 psf at 8,000. Snow load sizes the roof structure and everything carrying it. Combined with a 24-inch frost depth and Seismic Design Category D2, that means a foothills unit is genuinely a different building from a valley-floor unit with the same floor plan. A builder who quotes without asking your elevation has not priced the job.

Roughly three to six months for permitting according to independent northern Nevada sources, then typically five to eight months on site for a detached unit depending on size, ground and weather. Winter matters here: foundation work in frozen ground and roofing in snow both slow down or stop. The most reliable way to compress the total is a complete set of drawings that gets through plan check first time, which is a design cost rather than a construction one.

Sometimes, and it is one of the larger cost questions on the outskirts of Washoe County. A second dwelling adds load to a system sized for one, so expect a review and frequently a new or expanded system — which carries its own permit, its own engineering and its own soil percolation testing. Budget for it as a major line rather than a detail, and get it assessed before committing to a design, because the answer can change where the unit can sit.

Yes, and this is the exception people are most often caught by. Nevada's AB 396 constrains what local governments may require, but it does not touch private covenants. An HOA's CC&Rs can restrict or prohibit an ADU outright, and no state law currently overrides that. Read the CC&Rs before you spend money on design. This is a common issue in the master-planned communities around Reno — Somersett, ArrowCreek, Montreux and St James Village among them.