500 sq ft size cap
Nampa caps ADUs at 500 sq ft of habitable space — meaningfully smaller than Boise's 900, Meridian's 900, or Eagle's ~900. This single rule shapes everything about a Nampa build.
Nampa · ADU Cost 2026
How much does a Nampa ADU cost?
Updated: May 2026
Nampa ADUs run $115k–$200k turnkey for the smaller pre-approved plans that fit under Nampa's 500 sq ft size cap. Per-sqft cost matches Boise — what's different is the cap, the rules, and the rent. Below: which plans fit, what Nampa code allows that Boise doesn't, and where the math actually lands.
Nampa ADU cost — the headline number
A Nampa ADU costs $115k–$200k turnkey for the smaller plans that fit under Nampa's 500 sq ft cap — Goldfinch (280), Waxwing (396), Sandpiper (396), and Osprey (376) — and pushes to roughly $223k at Standard finish on the 491 sq ft Kingfisher, the largest plan that fits. Per-sqft cost is the same as Boise: lumber and labor don't care which side of the Ada/Canyon line you're on. What's different is the cap on size, more permissive owner-occupancy + parking + multi-ADU rules per Nampa's local code (verify Title 10 Chapter 7 for your parcel), and the lower local rent ceiling ($1,150/month 1BR median, $1,400/month 2BR median per Zumper, May 2026). Build cost is similar; the math just runs on smaller dwellings and slightly thinner rent — and often pencils better on cash-on-cash thanks to the lower land basis.
Nampa's defining rule
The 500 sq ft size cap shapes everything
Nampa caps ADUs at 500 sq ft of habitable space under its current development code (Title 10, Chapter 7 — Nampa city fee and code schedule, accessed May 2026). For comparison: Boise allows 900 sq ft, Meridian allows 900 (or 50% of primary, whichever is less), Eagle allows roughly 900, and Caldwell currently caps at 700 with a 1-bedroom limit. Nampa is the smallest of the four cities that ring Boise — by a wide margin.
That single rule rules out the Kestrel (695 sq ft, true 2-bedroom) entirely. It leaves five of the six pre-approved Boise plans buildable in Nampa, but the Kingfisher (491) just squeaks under — there is no margin for upsizing without redesign. For most Nampa ADU projects, the practical universe is the four studios (Goldfinch, Waxwing, Sandpiper, Osprey) plus the Kingfisher 1-bedroom.
Nampa also does not extend reciprocity for Boise's pre-approved plan set. Every Nampa ADU goes through Nampa's own building permit and plan review process under the Building Safety Division, separate from Ada County. We handle the Nampa submittal directly; you don't translate between jurisdictions.
What Nampa allows that other cities don't
Outside the size cap, Nampa is one of the most investor-friendly ADU jurisdictions in Idaho. Five rules that materially change the cost-and-feasibility math — all confirmed against Nampa Title 10 Chapter 7 and the Steadily Idaho ADU law summary (May 2026).
More permissive owner-occupancy
Nampa has historically been one of the only Idaho cities that does not require the owner to live in the primary or the ADU. Pure investor plays are legal here today, ahead of SB 1354's statewide preemption on 2026-07-01.
Multi-ADU allowed
Nampa code does not restrict the number of attached ADUs and allows up to two detached units in some zones — rare in Idaho. Two small rentals on one parcel is structurally possible inside city limits.
No off-street parking minimum
Nampa does not require a dedicated off-street parking space for the ADU. Saves driveway extension cost and opens up tight lots that wouldn't pencil in Eagle.
Lower property buy-in
Median Nampa home values run roughly $160k below Boise. Your land basis is smaller, which carries through the entire ROI calculation downstream.
Which pre-approved plans fit Nampa
Five of the six pre-approved Boise plans sit under Nampa's 500 sq ft cap. The Kestrel is too large to build as an ADU in Nampa today. Cost figures are Standard finish ($405/sqft) — see the cost calculator to model Essential or Premium finish ranges.
| Plan | Type | Size | Beds | Fits Nampa cap? | Cost at Standard finish |
|---|---|---|---|---|---|
| The Goldfinch | Type A | 280 sqft | Studio | Yes | $102k–$127k |
| The Waxwing | Type B | 396 sqft | Studio | Yes | $144k–$180k |
| The Kingfisher | Type C | 491 sqft | 1BR | Yes | $179k–$223k |
| The Kestrel | Type D | 695 sqft | 2BR | No — over 500 sqft | $253k–$315k |
| The Sandpiper | Type G-1 | 396 sqft | Studio | Yes | $144k–$180k |
| The Osprey | Type G-2 | 376 sqft | Studio | Yes | $137k–$171k |
Want Essential or Premium finish numbers? The same plans run roughly 16% lower at Essential ($340/sqft) and 18% higher at Premium ($480/sqft). Use the cost calculator to model exact ranges.
Iron Crest Remodel (Idaho contractor license RCE-6681702), our Treasure Valley construction partner, builds in Nampa as part of its 28-community service area.
Nampa city fees — what we know, what to pull
Nampa publishes its permit fee schedule and development impact fee schedule via the City of Nampa Building Safety Division and its Development Impact Fee program (Bulletin GA-11-2025-035, 2026 schedule). Both reference cityofnampa.us as the canonical source.
Honest framing: per-tier permit dollar amounts and Nampa's specific per-unit impact fee for a new dwelling unit are not published in scrape-friendly form today. The fee schedule PDF is behind a binary endpoint that requires manual download or a counter visit at 500 12th Ave S, Nampa. We pull the current numbers fresh on every quote rather than estimate from a stale figure.
Two structural notes that are public and matter for budgeting: (1) Nampa is the only Treasure Valley city that bundles utility connection (sewer, water, pressurized irrigation) into the development impact fee schedule — Meridian, Eagle, and Caldwell handle utility connection separately. (2) Nampa is in Canyon County, not Ada — there is no ACHD transportation impact fee, which saves roughly $5,803 versus the equivalent ADU build in Meridian or Eagle per ACHD's 2026 rate effective 2026-03-01.
Action item: before locking your budget, pull the current Nampa permit fee schedule and impact fee bulletin from cityofnampa.us — or let us pull it on your behalf during the free lot check.
Rent reality in Nampa
Nampa median rent runs $1,150/month for a 1-bedroom and $1,400/month for a 2-bedroom as of May 2026 (Zumper Nampa rent research, accessed 2026-05-24). Other sources range $1,095 (PadMapper, Feb 2026) to $1,463 (ApartmentList) — Zumper sits in the middle and is the most-recently-dated source.
For comparison: Boise median 1BR is roughly $1,479–$1,503 and 2BR runs $1,650–$1,900. Nampa rent is about 20% lower per unit. The cash-on-cash math often still favors Nampa because the lower land basis cancels most of the rent gap, and Nampa's multi-ADU rule lets you spread the smaller rent across two units on a qualifying parcel. The ROI calculator lets you swap in Nampa rent assumptions against any plan.
When Nampa beats Boise for ADU investors
Honest framing — Nampa isn't strictly better than Boise. It's structurally different. Four scenarios where the Nampa math wins on cash-on-cash.
Lower property entry cost = better cash-on-cash
Lower land basis + similar build cost means a higher percent return on capital, even with smaller rent dollars on the back end.
Multi-ADU rules unlock 2-rental parcels
On a lot zoned for it, two small units on one parcel is a path Boise zoning does not allow. Two Goldfinches or a Goldfinch + Sandpiper can pencil dramatically better than one larger unit.
NNU and college-corridor demand
Northwest Nazarene University in Nampa plus College of Idaho overflow from neighboring Caldwell drive steady 1BR and studio demand near Amity. ADUs lease faster than full-house rentals in this submarket.
Permits typically move faster
Canyon County jurisdiction generally runs ahead of Ada County on residential review. Nampa does not publish a hard SLA, but anecdotally beats Meridian and Eagle on plan check cycles.
When Boise still wins
Three reasons a Boise ADU build still beats Nampa for the right owner profile.
Bigger plans pencil bigger rents
Boise's 900 sq ft cap lets you build a real 2-bedroom (the Kestrel) that clears $1,650–$1,900/month. Nampa's 500 cap puts you in studio and small 1BR territory only.
Higher rent ceiling per unit
Boise 1BR median sits around $1,479–$1,503; Nampa 1BR median is $1,150 (Zumper, May 2026). Per-unit gross is meaningfully higher in Boise.
Deeper resale market
Boise has more buyers shopping ADU-equipped homes at exit. Nampa is catching up but is still a thinner resale pool for finished ADU comps.
Want the head-to-head? See the full Boise ADU cost guide for plan-by-plan pricing and the broader Boise impact fee detail.
Nampa ADU cost — frequently asked
ADU rules referenced below cite Nampa Title 10 Chapter 7 (city code, accessed May 2026), the Nampa development impact fee schedule (Bulletin GA-11-2025-035), and Zumper Nampa rent research dated May 23, 2026.
How much does a Nampa ADU cost in 2026?
A pre-approved Nampa ADU at Standard finish ($405/sqft) costs $115k–$200k turnkey for the plans that fit under Nampa's 500 sq ft size cap — Goldfinch ($102k–$127k), Waxwing ($144k–$180k), Sandpiper ($144k–$180k), Osprey ($137k–$170k), and Kingfisher ($179k–$223k). Per-sqft cost is the same as Boise — what's different is the cap on size, the lower local rent, and Canyon County's different fee schedule. Pull current Nampa permit and impact fee amounts from cityofnampa.us before locking your budget.
Can I build a Kestrel 2-bedroom in Nampa?
No. The Kestrel is 695 sq ft, which is 195 sq ft over Nampa's current 500 sq ft ADU size cap. If you want a 2-bedroom ADU, you're either in Boise (900 cap), Meridian (900 cap), or building it as a primary dwelling rather than an ADU in Nampa. The largest plan that fits Nampa today is the Kingfisher at 491 sq ft — a true 1-bedroom that just squeaks under the cap.
Can I build multiple ADUs on one Nampa lot?
In some zones, yes. Nampa code does not restrict the number of attached ADUs and allows up to two detached units in qualifying residential zones. This is one of the most permissive multi-unit ADU rules in Idaho. It does require parcel-by-parcel zoning confirmation — and if your parcel sits in unincorporated Canyon County rather than inside Nampa city limits, county rules apply instead. The Nampa Building Department or a lot check confirms which jurisdiction applies before you draw anything.
Does Nampa require owner-occupancy?
Third-party reporting describes Nampa as more permissive on owner-occupancy than Boise's pre-2023 rule, but the authoritative source is Nampa's Title 10 Chapter 7 development code — verify with City of Nampa Building Safety for your specific parcel and zone before locking in a pure-investor structure. Idaho Senate Bill 1354 preempts city-level owner-occupancy rules statewide effective 2026-07-01, which standardizes this across the Treasure Valley regardless of current local code.
What about Canyon County (outside Nampa city limits)?
Canyon County Development Services issues permits for parcels outside Nampa city limits. The codes overlap with Nampa's but aren't identical — county parcels often allow larger structures but have stricter septic and well requirements. Connection fees follow the utility districts that serve that parcel rather than Nampa's bundled impact fee schedule. We confirm which jurisdiction issues the permit on every project before scoping cost.
How does Nampa ADU rent compare to Boise?
Nampa median 1BR is $1,150/month and 2BR is $1,400/month (Zumper, May 2026). Boise 1BR sits around $1,479–$1,503 and 2BR is roughly $1,650–$1,900. Per-unit rent is meaningfully lower in Nampa — roughly 20% below Boise on a 1BR. The cash-on-cash math often still favors Nampa because your land basis and total project cost are also lower, and Nampa's multi-ADU rules let you spread that smaller rent across two units on one parcel if your lot qualifies.
Related Nampa & Treasure Valley resources
Boise ADU cost (baseline)
Full plan-by-plan pricing for the larger 900 sq ft cap.
Meridian ADU cost
Ada County sibling — 900 cap, ACHD impact fee applies.
Eagle ADU cost
EASD design review adds cost — premium submarket trade-off.
Caldwell ADU cost
Canyon County sibling — 700 cap, no ACHD fee.
Nampa service area
Neighborhoods, zoning notes, and lot context for Nampa.
Cost calculator
Model any sqft + finish combination against the 500 cap.
ROI calculator
Layer Nampa rent against any plan + finish combination.
Treasure Valley ADU guide
Pillar guide covering rules, plans, financing, and ROI.
Goldfinch (280 sqft)
Cap-rate king for Nampa — fits cleanly, lowest basis.
Waxwing (396 sqft)
Larger studio that still fits Nampa's 500 cap with room.
Kingfisher (491 sqft)
Largest plan that fits Nampa — only true 1BR option.
Free Nampa lot check
24-hour reply with jurisdiction, plan fit, and fees.
Free Lot Check · 24-Hour Response
Want a real number for your Nampa ADU?
Start with a free lot check — jurisdiction (city vs. Canyon County), plan fit under the 500 cap, and a current Nampa fee pull. Or call (208) 297-2036.