Home Additions and ADUs in Boise, Idaho
Sometimes the house you have is in the right place but is not big enough anymore. A room addition, a finished basement, a garage conversion, or a detached accessory dwelling unit in the backyard can solve that without the cost and disruption of moving. R2F Construction builds all of them in Boise and the surrounding cities, from the permit set through foundation, framing, and finish.
Boise rewrote its zoning code in 2023 and loosened the rules for ADUs considerably. That opened the door for a lot of homeowners who had been told no a few years ago. We will tell you honestly what your lot allows before you spend money on plans.
What We Do for
Additions & ADUs
Room additions
A primary suite, a bigger kitchen, a family room, or a second story. Foundation, framing, roofing tied into the existing structure, and finishes that match the house.
Detached ADUs
A backyard cottage with its own kitchen and bath. Boise allows up to 900 square feet or half the size of the main house, whichever is smaller, in most residential zones.
Garage conversions and attached ADUs
Turning an attached or detached garage into living space or a rental unit. Often the fastest path to an ADU because the shell already exists.
Basement finishing
Bedrooms, a bath, a family room, or a separate suite. Egress windows, moisture control, and proper insulation for Idaho winters.
Permits and engineering
Zoning check, site plan, structural engineering where required, and the building permit through the city or county. We run the process so you do not have to.
Roofing, windows, and exterior to match
Since we are also a roofing and window contractor, the addition gets the same premium roof and windows as the rest of the house, installed by the same crew.
What Additions and ADUs Cost in Boise
Per square foot of new or converted space, R2F pricing with premium materials
| Project Type | Mid-Range (per sq ft) | Premium (per sq ft) | Typical Total |
|---|---|---|---|
| Room addition | $170 – $255 | $255 – $425 | $34K – $128K |
| Garage conversion / attached ADU | $125 – $210 | $210 – $340 | $34K – $102K |
| Basement finish | $40 – $85 | $85 – $150 | $21K – $64K |
Detached ADUs with a full kitchen and bath generally price like a room addition plus the cost of running utilities to the new structure. Ranges include permits, foundation, framing, roofing, windows, mechanical, and finishes. Site conditions, utility distance, and engineering drive the spread.
What It Can Look Like
From First Call
to Final Walkthrough
- 01
Feasibility and free estimate
We check your zoning, setbacks, and lot coverage, look at where utilities are, and give you an honest read on what is possible and roughly what it costs.
- 02
Plans and permit
Drawings, engineering if the city requires it, and the permit application. Boise issues most ADU permits administratively, without a public hearing.
- 03
Foundation, framing, and shell
Excavation, foundation, framing, roofing, windows, and siding. We get the structure weather-tight before Idaho weather has a say.
- 04
Mechanical, finishes, and final inspection
Electrical, plumbing, HVAC, insulation, drywall, flooring, cabinets, and the final inspection and certificate of occupancy.
Additions & ADUs FAQ for
Boise Homeowners
What are the ADU rules in Boise?
Under Boise’s current zoning code, an accessory dwelling unit can be up to 900 square feet or 50 percent of the primary home, whichever is less. The old owner-occupancy requirement and the extra parking requirement were removed, and ADUs are allowed in the main residential zones with an administrative permit. The city updated the code again in 2025, so we confirm the current rules with Planning and Development Services at the start of every project. Meridian, Eagle, Nampa, and unincorporated Ada and Canyon County have their own rules.
How much does an ADU cost to build in Boise?
A garage conversion into a studio or one-bedroom ADU typically runs $34,000 to $102,000 depending on finish level and how much plumbing has to be added. A new detached ADU costs more, closer to room-addition pricing plus utility work, and the total depends heavily on size and site. We give a firm itemized number after a free site visit.
How long does a home addition take?
A single-room addition usually takes 8 to 14 weeks of construction after the permit is issued. Permitting itself adds several weeks, more if engineering or a variance is involved. A detached ADU is similar to a small house build and runs 3 to 5 months.
Will the addition match my existing house?
That is the goal, and it is where many additions fail. We match roof pitch, siding profile, window style, and trim, and we tie the new roof into the old one correctly so there is no leak-prone seam. Because we install roofing and windows ourselves, the whole exterior comes from one crew.
Can I rent out an ADU in Boise?
Yes. Boise no longer requires the owner to live on the property, so both the main house and the ADU can be rented. Short-term rental rules are separate and worth checking with the city if that is the plan.
Where We Work
Ready to Talk About
Your Additions & ADU?
Free, itemized, no-pressure estimate. We will tell you what it costs, what we recommend, and leave the decision to you.
📞 Call (208) 830-5654or fill out the form