Pre-Approved vs Custom ADU Plans

Which path should you pick — pre-approved or custom?

Pick pre-approved if any of the six City of Boise plans fit your lot and use case. You'll save 4-8 weeks at the city and $8,000-$15,000 in architecture fees, with no quality difference in the finished structure. Pick custom if a pre-approved plan doesn't fit — narrow lot, sloped lot, unusual use case, specific design preference. The pre-approved set covers about 70% of Boise lots; the rest go custom and accept the added time and cost.

What can you change on a pre-approved plan?

Material choices, finish levels, paint colors, cabinet styles, counter materials, fixture brands, flooring, tile, lighting — all fair game on a pre-approved plan. None of these touch the city-approved drawings, so the plan stays pre-approved. Most homeowners think the limit is more restrictive than it actually is; the freedom is in everything you can see and touch from inside the unit. For a finish-by-finish cost breakdown, see our Boise ADU cost guide.

Finish-level upgrades that don't trigger review

• Quartz, granite, or solid-surface counters in place of laminate
• Hardwood, engineered hardwood, or tile in place of LVP
• Designer cabinets, soft-close hardware, custom pulls
• Upgraded plumbing fixtures, pendant lighting, smart switches
• Tiled shower walls, custom shower glass, soaking tubs
• Mini-split or ductless HVAC instead of standard heat pump
• Higher-spec windows within the same opening size

What can't you change without losing pre-approved status?

The structural footprint, exterior elevations, window placement and size, door placement, roof pitch, and siding type are all fixed. If you modify any of these, the plan is no longer pre-approved and you're back to full design review (which takes the savings off the table). The city's reasoning is that pre-approved plans were vetted as a complete package — change any element and the whole package needs re-review.

When is a custom ADU the right call?

• Your lot is unusually narrow, deep, sloped, or oddly shaped (foothill lots, riverfront lots, corner lots with severe setbacks)
• You want a two-story ADU (the pre-approved plans are all single-story)
• You need a specific layout for accessibility (ADA wheelchair turning radii, single-level for aging parents with mobility devices the Kestrel doesn't accommodate)
• Your primary residence has a strong architectural style and you want the ADU to match exactly (Eagle, certain North End historic streets)
• You're combining the ADU with a major remodel of the primary house and want them designed as a single project
• You want exterior elevations that depart from the pre-approved aesthetic for view, light, or street-presence reasons
• Your HOA architectural committee requires custom matching to the main house (common in Banbury, Two Rivers, Spurwing)

How does the cost-of-time math actually work?

Custom plans add about 6-10 weeks to the front end. If your goal is rental income, that's roughly $5,000-$10,000 of foregone rent depending on the unit (a Kingfisher at $1,600/month over 8 weeks is $3,200; a Kestrel in Eagle at $2,000/month over 10 weeks is $5,000). Combined with the $8-15k design fee, custom typically costs $13,000-$25,000 more than pre-approved over the project lifecycle. Worth weighing against the design upside — and worth modeling against your numbers in the cost calculator.

If your goal is family or owner-use, the time cost is just patience — but the design fee is real money. Most aging-parent ADUs we build don't need anything custom; the pre-approved Kingfisher and Kestrel handle the use case cleanly with the right interior finish package.

Real example: when a custom plan paid for itself

We built a custom ADU on a 35-foot-wide lot in the Garden City 36th Street corridor where none of the six pre-approved plans fit the side-setback envelope. The custom design fee was $11,500 and the design-review stage added 7 weeks. The owner finished construction with a ground-floor unit specifically configured as a live-work space adjacent to the local brewery district, which leases at $400/month above the standard 1-bed comp. The premium recovers the design fee in under 30 months.

How do you know if your lot fits a pre-approved plan?

The simplest test: pull your parcel from the Ada County Assessor (or Canyon County Assessor in Nampa, Caldwell), confirm zoning with the city, measure the buildable envelope after subtracting setbacks and easements, then check whether any of the six plan footprints fit. We do this for free on every initial inquiry — the math is the same whether the lot is in Boise, Meridian, or Eagle. About 70% of Treasure Valley lots we've reviewed can host at least one pre-approved plan.

Common pitfalls when going custom

1. Hiring an architect who hasn't permitted in Boise. Each Treasure Valley jurisdiction has its own preferences, and an out-of-area architect's first set will get redlined on details a local would have anticipated.
2. Treating the design fee as the total custom premium. Add 6-10 weeks of foregone rent or holding cost, plus engineering review fees, plus survey fees if not already complete.
3. Designing for the dream house instead of the use case. A custom plan should solve a specific lot or use-case problem the pre-approved plans don't. If you're customizing for aesthetic preference alone, you're paying $15k for paint colors you could pick on a pre-approved plan.
4. Skipping the HOA early-engagement step. Custom is harder to take through HOA review than pre-approved precisely because there's no prior approval to point at.
5. Forgetting that custom plans need engineering stamps. Structural, energy, and sometimes mechanical engineers all bill against a custom set. The architect's fee is rarely the full picture — engineer fees alone can add $3,000-$6,000.

How do the six pre-approved plans compare?

Quick rundown of when each plan tends to win. Goldfinch (280 sq ft studio) is the cap-rate king — lowest build cost, smallest footprint, fits the tightest lots. Waxwing (396 sq ft studio) gives you a real living zone for ~$25k more; rents close to a Goldfinch but lives substantially better. Kingfisher (491 sq ft 1-bed) is the sweet-spot rental performer across Boise, Meridian, and Eagle. Kestrel (695 sq ft 2-bed) is the in-law-suite and small-family unit. Sandpiper and Osprey add a garage to a studio in different layouts — useful when the lot has no existing garage and the city's parking requirement is binding.

Real example: when pre-approved was the obvious win

We built a Standard-finish Kingfisher in a Meridian Bridgetower lot for a couple who wanted an in-law suite for the wife's mother. The site walk took 45 minutes; the contract signed two weeks later; permits came back from Meridian in 23 days. Total elapsed from first call to certificate of occupancy: 5 months and 2 weeks. The same project on a custom plan would have added at least $11,000 of architecture fees and pushed the C of O another 7-9 weeks. The wife's mother moved in three days after final inspection.

Pre-approved vs custom — frequently asked questions

Can I switch from pre-approved to custom mid-project?

Yes, but it resets the permitting clock. You'll abandon the pre-approved review path, lose any plan-check progress, and re-enter the queue for full design review. The architecture fee for the custom set still applies in full. We've seen this happen twice in two years; both times the homeowner regretted not deciding earlier.

Can I use a custom plan I already paid for on a different lot?

Maybe. The plan IP is yours (you paid for it), but each new lot triggers a fresh design-review cycle because setbacks, easements, and lot-specific conditions differ. Plan check fees apply each time. Modifications for the new lot are common and often non-trivial.

Are pre-approved plans really free, or are there hidden fees?

The plans themselves are published free by the City of Boise. Permit fees, plan-check fees, and impact fees still apply — those would apply on a custom plan too. The savings are the design-review time and the architectural fee, not the city fees.

Can I combine elements of two pre-approved plans?

No. Each pre-approved plan is a complete package. Cherry-picking elements (the Kingfisher kitchen with the Kestrel layout, for example) requires custom work and full design review. The plans aren't modular in that sense.

What's our recommendation?

Start with a free site walk to see if any of the six pre-approved plans fit your lot. We bring tape measure, parcel data, and the zoning code to the visit. About 70% of Boise and Meridian lots can take at least one pre-approved plan. If yes, you save real money and time. If not, going custom is fine — it just changes the math, and we'll show you the exact numbers before you commit.

Where to next

For the commercial side-by-side with feature matrix, cost breakdown, and per-scenario decision tree, see the Pre-Approved vs Custom ADU money page. If pre-approved is your path, the Boise pre-approved ADU plans overview is the next read. If custom is your path or you're not sure yet, the ADU design-build contractor overview walks through how a single-contract project actually runs. The ADU feasibility framework covers what determines whether your lot fits a pre-approved plan vs needs custom. Confirm fit on your parcel with the free lot check.