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ADU Rules in Honolulu, Hawaii

Complete guide to building an Accessory Dwelling Unit in Honolulu — zoning, setbacks, permits, costs, and more.

Max Size: 1,000 sq ft of floor area on zoning lots of 5,000 sq ft or more; 500 sq ft on lots up to 4,999 sq ft (ROH § 21-5.50-3(a)(1)(B), Ordinance 25-2, effective September 30, 2025). A legally built accessory structure that predates September 14, 2015 may be converted and exceed the cap by zoning adjustment if the director finds the floor area cannot practicably be reduced (§ 21-2.140-1(n)) Setbacks: 5 ft in R-3.5 through R-20 for a single-unit, two-unit or duplex dwelling and the ADU that shares its lot (Table 21-3.2); 8 ft in R-3.5 and 11 ft in R-5 to R-20 when the lot's floor area ratio exceeds 0.6 (§ 21-3.70-1(c)(3)(H)); 10 ft in the Country district (Table 21-3.1) Parking: Varies Verified: 2026-09-20

Researched by ADU Zoning Hub · verified 2026-09-20 against Honolulu planning code and Hawaii ADU law · methodology · 31 sources cited ↓

ADU Score: 7/10
Moderately friendly · how we score

Are ADUs allowed in Honolulu, HI? [1][2][3][4][5][6][7][8]

Yes. Honolulu allows ADUs on most residential lots. A detached unit can be up to 1,000 sq ft, set 5 ft back from the rear line. Parking varies by lot and unit size. Owner-occupancy rules vary — confirm with the city. A building permit is required and applications are reviewed through the standard permit process.

Maximum size1,000 sq ft of floor area on zoning lots of 5,000 sq ft or more; 500 sq ft on lots up to 4,999 sq ft (ROH § 21-5.50-3(a)(1)(B), Ordinance 25-2, effective September 30, 2025). A legally built accessory structure that predates September 14, 2015 may be converted and exceed the cap by zoning adjustment if the director finds the floor area cannot practicably be reduced (§ 21-2.140-1(n))
SetbacksRear 5 ft in R-3.5 through R-20 for a single-unit, two-unit or duplex dwelling and the ADU that shares its lot (Table 21-3.2); 8 ft in R-3.5 and 11 ft in R-5 to R-20 when the lot's floor area ratio exceeds 0.6 (§ 21-3.70-1(c)(3)(H)); 10 ft in the Country district (Table 21-3.1) · Side 5 ft in all residential districts (Table 21-3.2), rising to 8 ft in R-3.5 and 11 ft in R-5 to R-20 when floor area ratio exceeds 0.6; 10 ft in the Country district. Eaves and similar projections may extend 30 in. into a yard of 10 ft or less; lanais, balconies and covered walkways may not (§ 21-4.30(b))
ParkingOne off-street stall for the ADU, in addition to the main house's required parking; it may be a compact stall of 7 ft 6 in by 16 ft (§ 21-6.30(b), § 21-6.50(a)(2)-(3)). No ADU stall is required within 0.5 mile of a rail station, and the stall is waived on lots in the Primary Urban Center or ʻEwa development-plan areas within 800 ft of a city bus stop unless an ohana unit on the same lot already used that waiver. A pre-2015 accessory structure being converted can also seek a parking waiver by zoning adjustment (§ 21-2.140-1(n))
Owner-occupancyDropped from the code in 2025, but confirm the covenant form before recording: Ordinance 25-2's minimum covenant terms (§ 21-5.50-3(a)(2)(A)) require only long-term residential occupancy, no bed-and-breakfast or transient vacation use, no condominium (CPR) separation of the ADU, and lapse on removal; the 2015 ordinance's owner-occupancy clause is gone. DPP's ADU Declaration of Restrictive Covenants still posted on DocuShare is the 2017 version and contains an owner, family or designated-representative occupancy clause and a six-month minimum term, so ask DPP which form applies

Do I need a permit to build an ADU in Honolulu? [9][10][11][12][13][14][15][16][17][18][19][20]

Yes. Every ADU in Honolulu needs a building permit. Review process: Building permit from the Department of Planning and Permitting (DPP) through the HNL Build portal, with plans uploaded to ePlans/ProjectDox (paper plans are not accepted). Sequence: (1) ADU Public Facilities Pre-Check Form signed off by DPP zoning, the DPP Wastewater Branch or State Department of Health for septic lots, the Board of Water Supply, the Honolulu Fire Department and DPP roadway review, valid for 210 business days; (2) optional free CivCheck AI pre-review, which DPP opens to ADUs and ohana units; (3) plans stamped by a Hawaii-licensed architect or engineer where the work exceeds $40,000 (one story) or $35,000 (two stories); (4) prescreen, agency plan review and permit issuance; (5) record the ADU restrictive covenant at the Bureau of Conveyances or Land Court and file a certified copy with DPP before the permit issues; (6) inspections and certificate of occupancy. DPP building-permit line (808) 768-8220, zoning (808) 768-8015.

Permit fees$0 for the ADU's plan review and building permit: ROH § 18-6.5 waives both fees for the creation of an accessory dwelling unit, extended through June 30, 2030 by Ordinance 25-12 (no waiver if work started without a permit). For scale, ROH 18-6.2 would otherwise charge $700 plus $10 per $1,000 of value above $100,000 (about $2,200 on a $250,000 job) plus a 20 percent plan-review fee. Grading, grubbing and stockpiling permit fees processed with an ADU permit are waived too (§ 18A-2.4). A zoning adjustment, if needed, costs $200 initial review plus $400 processing (DPP, November 2025)
Typical timeline5-11 weeks for DPP's decision on a residential permit in 2026 (DPP reports 32.5 days on average for applications pre-checked with CivCheck and 73 days without; no ADU-specific target is published). From July 1, 2026, state Act 295 (2025) lets an applicant whose complete single-family application has waited 60 business days without full approval request an expedited permit backed by the licensed professional's certification and insurance. A zoning adjustment (parking or floor-area relief) is decided within 45 calendar days of acceptance or is deemed approved
Official Honolulu links:

Three things to know before you build in Honolulu

  • Start with the ADU Public Facilities Pre-Check Form, not drawings: sewer capacity (DPP Wastewater Branch) is the usual blocker, and the code only permits an ADU where wastewater, water, road and first-responder capacity are sufficient (§ 21-5.50-3(a)(1)(G)). The form is void 210 business days after the first agency signature
  • Count bathrooms before you design: on a lot under 7,000 sq ft with two or more dwellings, each unit may have at most 2 bathrooms (3 on 7,000-9,999 sq ft, 4 on 10,000 sq ft and up), one wet bar and one laundry room (§ 21-3.70-1(c)(3))
  • Check the whole lot's numbers, not just the ADU's: 50 percent maximum building area, 0.7 floor area ratio and 75 percent maximum impervious surface apply to everything on the lot, and yards jump to 8 or 11 ft once FAR passes 0.6 (Table 21-3.2, § 21-3.70-1(c)(3))

Last verified 2026-09-20 against Honolulu planning code. How we verify

Yes. Honolulu (the City and County covering all of Oʻahu) allows one accessory dwelling unit as an accessory use on any lot in the residential districts R-3.5 through R-20 or the Country district under ROH § 21-5.50-3(a), as rewritten by Ordinance 25-2 (in force since September 30, 2025). The ADU may be up to 1,000 sq ft on a zoning lot of 5,000 sq ft or more and 500 sq ft on a smaller lot, must meet the district's own 10-ft front and 5-ft side and rear yards, 25-30 ft height envelope and 50 percent building-area limit, and needs one off-street stall unless the lot is within 0.5 mile of a rail station. Before the building permit you need a DPP Public Facilities Pre-Check (sewer or septic capacity, water, fire access, road width) and a recorded covenant limiting the unit to long-term occupancy; owner-occupancy is no longer in the code's required covenant terms. Plan-review, building-permit, grading and city wastewater facility charges are waived for ADUs through June 30, 2030 (Ordinances 16-19 and 25-12), though the Board of Water Supply facilities charge still applies. State Act 39 (2024) requires the county to allow at least two ADUs per residentially zoned lot by December 31, 2026; as of September 2026 the code still allows one and the Council has asked the Legislature to repeal the mandate.

In Honolulu you will also hear an ADU called a ohana unit — from the Hawaiian word for extended family. The rules on this page apply either way.

Zoning & Size Requirements [1][2][3][4][5][6][7][8]

Yes — Honolulu allows ADUs. A detached ADU can typically be up to 1,000 sq ft under current Hawaii and Honolulu zoning rules.

See what this means for your lot — ask Honolulu ADU builders for a quote →

Allowed Zonesthe Country (C) district and every residential district (R-3.5, R-5, R-7.5, R-10 and R-20) as an accessory use with standards ("Ac*" in Table 21-5.1); not permitted in the AG-1 and AG-2 agricultural districts, the apartment (A-1 to A-3) or mixed-use districts, or on landlocked lots or lots in planned development housing or cluster housing (ROH § 21-5.50-3(a)(1)(A))
Max Size (Detached)1,000 sq ft of floor area on zoning lots of 5,000 sq ft or more; 500 sq ft on lots up to 4,999 sq ft (ROH § 21-5.50-3(a)(1)(B), Ordinance 25-2, effective September 30, 2025). A legally built accessory structure that predates September 14, 2015 may be converted and exceed the cap by zoning adjustment if the director finds the floor area cannot practicably be reduced (§ 21-2.140-1(n))
Max Size (Attached)Same 1,000 sq ft / 500 sq ft caps by lot size. An ADU may be new construction or a conversion, attached (as in a two-unit dwelling) or detached, or a converted attic or basement (§ 21-5.50-3(a)(1)(D)); it must have its own kitchen, bedroom and bathroom (§ 21-10.1 definition)
Max Size (JADU)No junior-ADU category in Honolulu. The other accessory unit is the ohana unit (§ 21-5.50-3(c)): no floor-area cap since Ordinance 06-15, but its occupants must be related by blood, adoption, guardianship or marriage to the family in the main house, and its parking is the same as the main dwelling's. A lot may have both an ohana unit and one ADU
Max Height25-30 ft building envelope in the residential districts: a plane 25 ft above the high point of the buildable-area boundary, or 30 ft parallel to grade where the two do not meet; any part of a structure above 15 ft must step back 1 ft for every 2 ft of extra height from the side and rear buildable-area lines, and above 20 ft from the front (Table 21-3.2, § 21-3.70-1(c)(1)-(2)). Country district: 15-30 ft (Table 21-3.1)
Max UnitsOne ADU per zoning lot, including lots that already hold two principal dwellings; an ohana unit does not count toward the one-ADU limit, so a lot can carry a main house, an ohana unit and an ADU if every development standard is met (§ 21-5.50-3(a)(1)(E) and (c)(1)(C)). State Act 39 (2024) requires the county to allow at least two ADUs or the reasonable equivalent on residentially zoned lots by December 31, 2026, after which permits for up to two ADUs may not be denied on unit count alone; Honolulu had not amended the one-ADU rule as of September 2026

Setback Requirements [1][2][3][4][5][6][7][8]

Honolulu requires a rear setback of about 5 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is set by local rules (confirm with the city).

Rear Setback5 ft in R-3.5 through R-20 for a single-unit, two-unit or duplex dwelling and the ADU that shares its lot (Table 21-3.2); 8 ft in R-3.5 and 11 ft in R-5 to R-20 when the lot's floor area ratio exceeds 0.6 (§ 21-3.70-1(c)(3)(H)); 10 ft in the Country district (Table 21-3.1)
Side Setback5 ft in all residential districts (Table 21-3.2), rising to 8 ft in R-3.5 and 11 ft in R-5 to R-20 when floor area ratio exceeds 0.6; 10 ft in the Country district. Eaves and similar projections may extend 30 in. into a yard of 10 ft or less; lanais, balconies and covered walkways may not (§ 21-4.30(b))
Front Setback10 ft in every residential district for a dwelling and its ADU (Table 21-3.2), with any part of the structure above 20 ft stepped back a further 1 ft per 2 ft of height; 15 ft in the Country district (Table 21-3.1). No parking may sit in a required yard (§ 21-4.30(d))
Parking RequiredOne off-street stall for the ADU, in addition to the main house's required parking; it may be a compact stall of 7 ft 6 in by 16 ft (§ 21-6.30(b), § 21-6.50(a)(2)-(3)). No ADU stall is required within 0.5 mile of a rail station, and the stall is waived on lots in the Primary Urban Center or ʻEwa development-plan areas within 800 ft of a city bus stop unless an ohana unit on the same lot already used that waiver. A pre-2015 accessory structure being converted can also seek a parking waiver by zoning adjustment (§ 21-2.140-1(n))
Owner OccupancyDropped from the code in 2025, but confirm the covenant form before recording: Ordinance 25-2's minimum covenant terms (§ 21-5.50-3(a)(2)(A)) require only long-term residential occupancy, no bed-and-breakfast or transient vacation use, no condominium (CPR) separation of the ADU, and lapse on removal; the 2015 ordinance's owner-occupancy clause is gone. DPP's ADU Declaration of Restrictive Covenants still posted on DocuShare is the 2017 version and contains an owner, family or designated-representative occupancy clause and a six-month minimum term, so ask DPP which form applies
Min Lot SizeNo minimum lot size since September 30, 2025: any residential or Country lot, including those under the old 3,500 sq ft floor, qualifies for a 500 sq ft ADU, and lots of 5,000 sq ft or more for 1,000 sq ft (§ 21-5.50-3(a)(1)(B)). The lot must still have adequate sewer or an approved septic system, water, fire access and first-responder capacity (§ 21-5.50-3(a)(1)(G)), and DPP's Pre-Check form asks for direct access to a street with a 20-ft paved roadway

Permit Process & Fees [9][10][11][12][13][14][15][16][17][18][19][20]

An ADU permit in Honolulu goes through a standard permit review. Typical timeline: 5-11 weeks for DPP's decision on a residential permit in 2026 (DPP reports 32.5 days on average for applications pre-checked with CivCheck and 73 days without; no ADU-specific target is published). From July 1, 2026, state Act 295 (2025) lets an applicant whose complete single-family application has waited 60 business days without full approval request an expedited permit backed by the licensed professional's certification and insurance. A zoning adjustment (parking or floor-area relief) is decided within 45 calendar days of acceptance or is deemed approved. Fees range from $0 for the ADU's plan review and building permit: ROH § 18-6.5 waives both fees for the creation of an accessory dwelling unit, extended through June 30, 2030 by Ordinance 25-12 (no waiver if work started without a permit). For scale, ROH 18-6.2 would otherwise charge $700 plus $10 per $1,000 of value above $100,000 (about $2,200 on a $250,000 job) plus a 20 percent plan-review fee. Grading, grubbing and stockpiling permit fees processed with an ADU permit are waived too (§ 18A-2.4). A zoning adjustment, if needed, costs $200 initial review plus $400 processing (DPP, November 2025).

Approval ProcessBuilding permit from the Department of Planning and Permitting (DPP) through the HNL Build portal, with plans uploaded to ePlans/ProjectDox (paper plans are not accepted). Sequence: (1) ADU Public Facilities Pre-Check Form signed off by DPP zoning, the DPP Wastewater Branch or State Department of Health for septic lots, the Board of Water Supply, the Honolulu Fire Department and DPP roadway review, valid for 210 business days; (2) optional free CivCheck AI pre-review, which DPP opens to ADUs and ohana units; (3) plans stamped by a Hawaii-licensed architect or engineer where the work exceeds $40,000 (one story) or $35,000 (two stories); (4) prescreen, agency plan review and permit issuance; (5) record the ADU restrictive covenant at the Bureau of Conveyances or Land Court and file a certified copy with DPP before the permit issues; (6) inspections and certificate of occupancy. DPP building-permit line (808) 768-8220, zoning (808) 768-8015
Review Timeline5-11 weeks for DPP's decision on a residential permit in 2026 (DPP reports 32.5 days on average for applications pre-checked with CivCheck and 73 days without; no ADU-specific target is published). From July 1, 2026, state Act 295 (2025) lets an applicant whose complete single-family application has waited 60 business days without full approval request an expedited permit backed by the licensed professional's certification and insurance. A zoning adjustment (parking or floor-area relief) is decided within 45 calendar days of acceptance or is deemed approved
Permit Fees$0 for the ADU's plan review and building permit: ROH § 18-6.5 waives both fees for the creation of an accessory dwelling unit, extended through June 30, 2030 by Ordinance 25-12 (no waiver if work started without a permit). For scale, ROH 18-6.2 would otherwise charge $700 plus $10 per $1,000 of value above $100,000 (about $2,200 on a $250,000 job) plus a 20 percent plan-review fee. Grading, grubbing and stockpiling permit fees processed with an ADU permit are waived too (§ 18A-2.4). A zoning adjustment, if needed, costs $200 initial review plus $400 processing (DPP, November 2025)
Impact FeesHonolulu levies no general impact fee. The city wastewater system facility charge, $7,013 per equivalent single-family unit from January 1, 2026 and $7,539 from July 1, 2026 with an ADU counted as 0.7 ESDU (Ordinance 25-27), is waived for ADUs through June 30, 2030 (ROH § 43-10.7, Ordinances 16-19 and 25-12). Not waived: the Board of Water Supply water system facilities charge of $185.33 per fixture unit for single-family service, minimum 20 fixture units (about $3,700), plus any meter upsizing, and State Department of Health review of a cesspool or septic system. Once occupied, the ADU pays its own monthly sewer base charge ($43.70 from January 1, 2026, $33.19 from July 1, 2026) plus volume charges
Plan CheckPrescreen for plan-format completeness, then routing to every reviewing agency with comments returned through ProjectDox; DPP's One Time Review (OTR-60) checklist applies to residential work. The plan-review fee (normally 20 percent of the permit fee, ROH 18-6.1) is waived for an ADU. Pre-checking the set in CivCheck cut corrections per permit from 23.5 to 7.7 on average (DPP)
Pre-Approved PlansNo pre-approved plans. DPP has no pre-approved or stock ADU plan program (checked September 2026); every ADU needs its own plan set, stamped by a Hawaii-licensed architect or engineer once the work exceeds $40,000 for a one-story or $35,000 for a two-story structure

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Construction Costs [21][22][23][24][25][26]

Building an ADU in Honolulu typically costs $150,000-$450,000 ($250-$550 per sq ft); a garage conversion runs $150,000-$225,000.

See what this means for your lot — ask Honolulu ADU builders for a quote →

Average Build Cost$150,000-$450,000
Cost per Sq Ft$250-$550
Garage Conversion$150,000-$225,000
Prefab ADU (Installed)$100,000-$240,000

Finance Your ADU Project

Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.

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Rental Income Potential [27][28][29][30][31]

A 2-bedroom ADU in Honolulu rents for around $2,600-$3,900/mo, an estimated Roughly 7-13% gross rental yield: a 500 sq ft one-bedroom built for $150,000-$250,000 and rented at $2,000-$2,800/mo returns about 10-16% gross, an 800-1,000 sq ft two-bedroom at $350,000-$450,000 and $2,600-$3,900/mo ab.

Avg Rent (1 Bedroom)$2,000-$2,800/mo
Avg Rent (2 Bedroom)$2,600-$3,900/mo
Short-Term RentalNo. The recorded ADU covenant limits the unit to long-term residential occupancy and bars bed-and-breakfast or transient vacation use (§ 21-5.50-3(a)(2)(A)(i)).
Est. Annual ROIRoughly 7-13% gross rental yield: a 500 sq ft one-bedroom built for $150,000-$250,000 and rented at $2,000-$2,800/mo returns about 10-16% gross, an 800-1,000 sq ft two-bedroom at $350,000-$450,000 and $2,600-$3,900/mo ab.

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Recent Law Changes

What's Changed Recently

  • Ordinance 25-2 (signed January 3, 2025; ADU provisions effective September 30, 2025) moved the ADU rules to ROH § 21-5.50-3(a), replaced the 400/800 sq ft caps and 3,500 sq ft minimum lot with 500 sq ft (lots under 5,000 sq ft) and 1,000 sq ft (5,000 sq ft and up), allowed an ADU on lots that already have an ohana unit or two principal dwellings, kept the 0.5-mile rail-station parking exemption and added an 800-ft bus-stop waiver in the Primary Urban Center and ʻEwa areas, and dropped owner-occupancy from the covenant terms the code requires
  • Ordinance 25-12 (2025) extended the ADU fee incentives of Ordinance 16-19 (waived plan-review and building-permit fees, grading permit fees and the wastewater system facility charge) from June 30, 2025 to June 30, 2030; Ordinance 25-41 (2025) restated the waiver as ROH § 18-6.5(e) and 18A-2.4(f)
  • Ordinance 25-27 (Bill 60 (2024), effective October 1, 2025) made ADUs their own sewer customer class: 0.7 ESDU for the wastewater system facility charge, now $7,013 per ESDU and rising to $7,539 on July 1, 2026 and $10,593 by July 2030, and a separate monthly base charge per ADU
  • State Act 39 (SB 3202, 2024) requires each county to allow at least two ADUs or the reasonable equivalent on residentially zoned lots by December 31, 2026, bars new private covenants from limiting ADU count or long-term rental, and after the deadline stops a county from denying up to two ADUs on unit count alone. The Honolulu Council adopted Resolution 25-271 (September 2025) asking the 2026 Legislature to repeal the mandate; the 2026 session passed no bill amending it
  • State Act 295 (SB 66, 2025), effective July 1, 2026 through June 30, 2031: an applicant for a single-family or multi-family building permit that has been complete for 60 business days without full approval may request an expedited permit on the licensed professional's certification, $2 million insurance and indemnity
  • DPP moved permit intake to the HNL Build portal and opened free CivCheck AI plan pre-review to ADUs and ohana units (2025-2026), reporting 32.5-day average decisions for CivCheck applications against 73 days without; DPP's April 2026 LUO compilation shows no ADU changes after Ordinance 25-2

Tips for Building an ADU in Honolulu

  • Start with the ADU Public Facilities Pre-Check Form, not drawings: sewer capacity (DPP Wastewater Branch) is the usual blocker, and the code only permits an ADU where wastewater, water, road and first-responder capacity are sufficient (§ 21-5.50-3(a)(1)(G)). The form is void 210 business days after the first agency signature
  • Count bathrooms before you design: on a lot under 7,000 sq ft with two or more dwellings, each unit may have at most 2 bathrooms (3 on 7,000-9,999 sq ft, 4 on 10,000 sq ft and up), one wet bar and one laundry room (§ 21-3.70-1(c)(3))
  • Check the whole lot's numbers, not just the ADU's: 50 percent maximum building area, 0.7 floor area ratio and 75 percent maximum impervious surface apply to everything on the lot, and yards jump to 8 or 11 ft once FAR passes 0.6 (Table 21-3.2, § 21-3.70-1(c)(3))
  • Get the permit before you build: the plan-review, building-permit and wastewater-charge waivers are lost if work starts without a permit (§ 18-6.5), and Ordinance 25-40 (September 2025) tightened LUO enforcement and fines
  • If your lot is already under a condominium property regime (CPR), ask DPP first: the required covenant bars creating a CPR that separates the ADU, and DPP has treated existing CPR lots as ineligible, though that limit is not written in the LUO text
  • Family housing? Compare an ohana unit: no floor-area cap, but relatives only and full main-house parking; the ADU can be rented to anyone on a long-term basis and needs one stall. Both can share one lot
  • Cost basis: Oʻahu design-build guides published April-July 2026 put standard-finish new construction at $450-$650 per sq ft and an 800 sq ft unit at $380,000-$520,000 all-in, while an architect's 2025-26 cost guide and an April 2026 property-management guide quote $250-$300 per sq ft and $105,000-$250,000 for 400-800 sq ft; garage or carport conversions $150,000-$225,000 (April 2026); prefab figures are a Hawaii kit vendor's $200-$400 per sq ft applied to 500-600 sq ft and should be confirmed with a site-specific quote
  • Cost basis (2026-09-20 re-verification): short term allowed: No. The recorded ADU covenant limits the unit to long-term residential occupancy and bars bed-and-breakfast or transient vacation use (§ 21-5.50-3(a)(2)(A)(i)). DPP enforces short-term rentals as stays under 30 consecutive days, and new short-term rentals are allowed only in resort-zoned and a few apartment-zoned areas, never in the residential districts where ADUs are built (Ordinances 22-7, 24-14, 25-52) | roi estimate: Roughly 7-13% gross rental yield: a 500 sq ft one-bedroom built for $150,000-$250,000 and rented at $2,000-$2,800/mo returns about 10-16% gross, an 800-1,000 sq ft two-bedroom at $350,000-$450,000 and $2,600-$3,900/mo about 7-11%, before vacancy, Hawaii general excise tax (4.5% on Oʻahu rent), property tax, insurance, the ADU's own sewer bill and financing

ADU Builders in Honolulu

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Sources & References

All data on this page is sourced from official government records and verified market data. View our full methodology.

  1. Revised Ordinances of Honolulu Chapter 21 (Land Use Ordinance), DPP compilation revised April 2026 (posted May 2026) — Table 21-5.1, § 21-5.50-3, Table 21-3.2, § 21-3.70-1, § 21-6.30(b), § 21-6.50 Municipal Code — Accessed 2026-09-20
  2. Revised Ordinances of Honolulu Chapter 21 (LUO), DPP compilation revised September 2025 Municipal Code — Accessed 2026-09-20
  3. Honolulu Ordinance 25-2 (Bill 64 (2023), CD2, FD2), signed January 3, 2025 — § 21-5.50-3(a), Section 34 (parking), Section 104 (effective date) Municipal Code — Accessed 2026-09-20
  4. Land Use Ordinance Update — Honolulu Department of Planning and Permitting Planning Department — Accessed 2026-09-20
  5. DPP Ordinances (ROH) page — Chapter 21 compilations and recent ordinances Planning Department — Accessed 2026-09-20
  6. Act 39, Session Laws of Hawaii 2024 (SB 3202) — accessory dwelling units on residentially zoned lots State Law — Accessed 2026-09-20
  7. Honolulu City Council Resolution 25-271 — 2026 HSAC package proposal to repeal Act 39's ADU requirements Municipal Code — Accessed 2026-09-20
  8. DPP Zoning Adjustment: Accessory Dwelling Units (ADUs) Conversion — Application Instructions (November 26, 2025) Planning Department — Accessed 2026-09-20
  9. DPP Building Permit (Plans Required) — process, required documents (ADU Pre-Check Form, Restrictive Covenant) Planning Department — Accessed 2026-09-20
  10. DPP Accessory Dwelling Unit (ADU) Public Facilities Pre-Check Form and instructions Planning Department — Accessed 2026-09-20
  11. DPP ADU Declaration of Restrictive Covenants (2017 form on DocuShare) Planning Department — Accessed 2026-09-20
  12. DPP Building Permit Fee Calculator — ROH 18-6.1 plan review and 18-6.2 permit fee tiers Planning Department — Accessed 2026-09-20
  13. Honolulu Ordinance 25-12 (Bill 63 (2024), CD1) — extends ADU fee incentives of Ordinance 16-19 to June 30, 2030 Municipal Code — Accessed 2026-09-20
  14. Honolulu Ordinance 25-41 (Bill 41 (2025), CD1) — ROH § 18-6.5 and 18A-2.4 ADU fee waivers as restated Municipal Code — Accessed 2026-09-20
  15. Honolulu Ordinance 20-20 — summary of the Ordinance 16-19 ADU waivers (wastewater facility charge, grading, plan review and building permit fees) Municipal Code — Accessed 2026-09-20
  16. Honolulu Ordinance 25-27 (Bill 60 (2024), CD2) — sewer service charges, ADU 0.7 ESDU, Appendix 43-C wastewater system facility charges Municipal Code — Accessed 2026-09-20
  17. Board of Water Supply — Water System Facilities Charge schedule Government Data — Accessed 2026-09-20
  18. DPP Getting Started With CivCheck — eligibility (ADUs, ohana units) and 32.5-day vs 73-day review figures Planning Department — Accessed 2026-09-20
  19. DPP One Time Review (OTR-60) checklist for residential building permits Planning Department — Accessed 2026-09-20
  20. Act 295, Session Laws of Hawaii 2025 (SB 66) — expedited permits after 60 business days, effective July 1, 2026 state_statute — Accessed 2026-09-20
  21. Warrior Construction — Oahu ADU Costs vs. Rental Income: The 2026 Financial Guide (May 26, 2026) industry — Accessed 2026-09-20
  22. Warrior Construction — 10 Things You Should Know About Hawaii's New ADU Rules (April 26, 2026, updated June 5, 2026) industry — Accessed 2026-09-20
  23. Hawaii Home Sales & Management — ADUs on Oʻahu: What Homeowners Need to Know in 2026 (April 8, 2026) industry — Accessed 2026-09-20
  24. Home Planning Hawaii / Architect Honolulu — Cost Per Square Foot to Build or Remodel in Honolulu: 2026 Realistic Expectations (July 13, 2026) industry — Accessed 2026-09-20
  25. Boom Hawaii Builders — Cost Per Square Foot Hawaii: What to Budget in 2026 (March 31, 2026, updated July 23, 2026) industry — Accessed 2026-09-20
  26. DC Structures — Hawaii Prefab ADUs (December 2025, updated January 2026) industry — Accessed 2026-09-20
  27. HUD FY2026 Fair Market Rents — Urban Honolulu, HI MSA (0BR $1,877, 1BR $2,016, 2BR $2,642, 3BR $3,674) Government Data — Accessed 2026-09-20
  28. Warrior Construction — Oahu ADU Costs vs. Rental Income: The 2026 Financial Guide (May 26, 2026) industry — Accessed 2026-09-20
  29. Hawaii Home Sales & Management — ADUs on Oʻahu (April 8, 2026) rent table industry — Accessed 2026-09-20
  30. DPP Short-Term Rentals page — STRs enforced as under 30 consecutive days; permitted areas Planning Department — Accessed 2026-09-20
  31. Department of Environmental Services FAQ — ADUs billed as separate sewer dwelling units Government Data — Accessed 2026-09-20

Frequently Asked Questions

Can I build an ADU in Honolulu?

Yes. ADUs are allowed in the Country (C) district and every residential district (R-3.5, R-5, R-7.5, R-10 and R-20) as an accessory use with standards ("Ac*" in Table 21-5.1); not permitted in the AG-1 and AG-2 agricultural districts, the apartment (A-1 to A-3) or mixed-use districts, or on landlocked lots or lots in planned development housing or cluster housing (ROH § 21-5.50-3(a)(1)(A)) in Honolulu. The maximum size for a detached ADU is 1,000 sq ft of floor area on zoning lots of 5,000 sq ft or more; 500 sq ft on lots up to 4,999 sq ft (ROH § 21-5.50-3(a)(1)(B), Ordinance 25-2, effective September 30, 2025). A legally built accessory structure that predates September 14, 2015 may be converted and exceed the cap by zoning adjustment if the director finds the floor area cannot practicably be reduced (§ 21-2.140-1(n)). Owner-occupancy: Dropped from the code in 2025, but confirm the covenant form before recording: Ordinance 25-2's minimum covenant terms (§ 21-5.50-3(a)(2)(A)) require only long-term residential occupancy, no bed-and-breakfast or transient vacation use, no condominium (CPR) separation of the ADU, and lapse on removal; the 2015 ordinance's owner-occupancy clause is gone. DPP's ADU Declaration of Restrictive Covenants still posted on DocuShare is the 2017 version and contains an owner, family or designated-representative occupancy clause and a six-month minimum term, so ask DPP which form applies.

How much does an ADU cost in Honolulu?

ADU construction in Honolulu typically costs $150,000-$450,000. Garage conversions run $150,000-$225,000, and prefab ADUs cost $100,000-$240,000.

How much can I rent an ADU for in Honolulu?

Average ADU rents in Honolulu are $2,000-$2,800/mo for a 1-bedroom and $2,600-$3,900/mo for a 2-bedroom unit.

Do I need parking for an ADU in Honolulu?

One off-street stall for the ADU, in addition to the main house's required parking; it may be a compact stall of 7 ft 6 in by 16 ft (§ 21-6.30(b), § 21-6.50(a)(2)-(3)). No ADU stall is required within 0.5 mile of a rail station, and the stall is waived on lots in the Primary Urban Center or ʻEwa development-plan areas within 800 ft of a city bus stop unless an ohana unit on the same lot already used that waiver. A pre-2015 accessory structure being converted can also seek a parking waiver by zoning adjustment (§ 21-2.140-1(n)). Check with Honolulu planning department for the latest Hawaii ADU parking rules, as many states have relaxed requirements in recent years.

How long does it take to get an ADU permit in Honolulu?

The permit review timeline in Honolulu is 5-11 weeks for DPP's decision on a residential permit in 2026 (DPP reports 32.5 days on average for applications pre-checked with CivCheck and 73 days without; no ADU-specific target is published). From July 1, 2026, state Act 295 (2025) lets an applicant whose complete single-family application has waited 60 business days without full approval request an expedited permit backed by the licensed professional's certification and insurance. A zoning adjustment (parking or floor-area relief) is decided within 45 calendar days of acceptance or is deemed approved. Fees range from $0 for the ADU's plan review and building permit: ROH § 18-6.5 waives both fees for the creation of an accessory dwelling unit, extended through June 30, 2030 by Ordinance 25-12 (no waiver if work started without a permit). For scale, ROH 18-6.2 would otherwise charge $700 plus $10 per $1,000 of value above $100,000 (about $2,200 on a $250,000 job) plus a 20 percent plan-review fee. Grading, grubbing and stockpiling permit fees processed with an ADU permit are waived too (§ 18A-2.4). A zoning adjustment, if needed, costs $200 initial review plus $400 processing (DPP, November 2025).

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Honolulu ADU FAQ

Answers to every common question about building an ADU in Honolulu — costs, rules, permits, rental income.

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Honolulu ADU Costs

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About this information: This page is an informational summary of publicly available regulations - it is not legal, financial, or professional advice, and it is not a substitute for confirming requirements with your local planning department. Rules change frequently; always verify current requirements before designing, budgeting, or building. Last verified: 2026-09-20. Contractors we introduce are independent businesses - verify license and insurance directly before hiring. Spotted an error? Tell us - we verify against primary sources and correct quickly.

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