Thinking about adding an ADU to your Boise property? We handle the whole thing. Floor plans, permits, engineering, and construction — all under one roof. We know Boise zoning inside and out, so you don’t have to.
The cost to build a detached ADU in Boise typically averages around $275 per square foot, with a realistic range of $275 to $325 per square foot depending on design choices, site conditions, utility connections, and finishes. Infill lots and constrained sites may require additional coordination that can affect overall cost.
We offer complimentary project quotes to help homeowners and investors understand expected costs before moving forward.
The first step in building an ADU is an in-depth site assessment. This includes reviewing zoning, setbacks, buildable area, utility access, and other site conditions that may affect feasibility or cost. A detailed assessment early in the process creates a strong foundation and helps avoid delays later.
Mode Homes offers site assessments as a standalone service for property owners considering an ADU.
During this phase, clients can either select from our curated ADU floor plan library or work with our team through a custom design-build process. Our pre-designed plans offer a streamlined path for many properties, while custom designs allow flexibility for unique site conditions, layouts, or architectural preferences. In both cases, we coordinate permit-ready drawings, structural engineering, and project specifications to ensure the design aligns with zoning requirements, budget, and long-term use.
Once budgets and scopes are finalized, we assist with contracting and preparation for construction.
ADU permitting in Boise requires coordination with city planning and building departments. Our team prepares and submits permit applications and responds to plan review comments to help move projects efficiently toward approval.
Once permits are approved, construction begins. Successful ADU construction depends on clear documentation, organization, and consistent site supervision. Our team manages the build from site work through final inspections to deliver a completed ADU ready for occupancy.
The first step is determining whether your property meets zoning and setback requirements. We’ve built a tool called SitePlanr that allows you to enter your address to quickly check eligibility.
In addition to city zoning, homeowners should review any HOA rules or architectural restrictions, as HOAs can limit or prohibit ADUs even when city zoning allows them.
The Treasure Valley rental market is tight and demand isn’t slowing down. For most Boise homeowners, an ADU is one of the smartest things you can do with land you already own.
ADU timelines vary based on zoning requirements, site conditions, design complexity, and permitting review times. Below is a typical timeline for a detached ADU project in Boise, assuming no unusual constraints.
During this phase, zoning, setbacks, buildable area, utility access, and site constraints are reviewed to confirm whether an ADU is feasible and identify potential challenges early.
This phase includes developing permit-ready drawings, coordinating structural engineering, finalizing specifications, and submitting permit applications to the City of Boise. Review timelines can vary depending on project complexity and city workload.
Construction timelines depend on ADU size, level of finish, site access, and utility connections. Clear documentation, scheduling, and consistent site supervision are key factors in keeping projects on track.
Detached ADUs in Boise typically range from $250 to $350 per square foot depending on size, design, and site conditions. So, for a 700 square foot unit there is a range of $175,000 to $245,000 total cost. Utility connections, access, and finishes can affect final cost. We provide detailed budgets during Project Development so you understand the full investment before construction begins.
An ADU, or Accessory Dwelling Unit, is a smaller secondary home built on the same lot as a primary residence. ADUs are sometimes referred to as a granny flat, guest house, backyard cottage, in-law suite, or carriage house.
An ADU can be attached to the main home, converted from an existing space like a garage, or built as a detached structure in the backyard. Most ADUs include a kitchen, bathroom, living area, and sleeping space, making them fully independent living units.
Homeowners build ADUs for many reasons, including rental income, housing for family members, downsizing on their own property, or increasing long-term property value.
ADU size limits depend on the city and zoning rules where the property is located. Each city in the Treasure Valley has its own regulations, so it’s important to verify the specific requirements for your address.
In Boise, a detached ADU can be up to 900 square feet or 70% of the size of the primary home, whichever is less. Additional rules may apply related to height, setbacks, lot size, and lot coverage.
Because regulations vary, it’s best to review your property early in the planning process to confirm what is allowed before moving into design.
Most ADU projects take 4 to 6 months to construct after permits are approved. Design and permitting typically take an additional 1 to 3 months depending on complexity and city review timelines.
Eligibility depends on zoning, lot size, setbacks, and access. Boise’s modern zoning code allows ADUs in many residential areas, but each property is different. We can help review feasibility before you move forward. Use our free tool siteplanr.com to place an ADU on your lot.
Yes. Even if city zoning allows an ADU, your HOA may have restrictions. It’s important to review HOA rules early in the process.
Some lenders may consider projected rental income, but policies vary. It’s best to speak directly with a lender. We help ensure your plans and budget are structured clearly for underwriting.
Yes. We offer a library of ready-to-build ADU plans. You can build a plan as designed or customize it during Project Development.
Schedule a free consultation with our ADU experts. We’ll assess your property, review your goals, and deliver a detailed, no-obligation estimate.
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