Everything homeowners need to know about building an accessory dwelling unit in Gresham - size limits, setbacks, permits, and how Oregon's early statewide ADU mandate shaped the city's streamlined, by-right process.
Last verified: August 2026
8/10 · Very ADU-friendly
900 sq ft*
Max ADU size
No taller than home
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes the City of Gresham Development Code, Section 10.0100 (Accessory Dwellings), for general reference - it is not legal advice. Regulations change; always confirm current requirements with Gresham Urban Design & Planning before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Freestanding (detached, new build or converted structure)
900 sq ft or 75% of the primary dwelling's floor area, whichever is smaller
Cannot exceed the height of the primary dwelling; some lower-density zones also step the roof height down near the rear lot line
Must sit no closer to the street than the primary dwelling; a rear setback of 10 ft (5 ft if the lot has an alley) and 5 ft side setback apply
Attached (addition, above-garage, or interior conversion)
Same 900 sq ft / 75% formula
Follows the applicable district height standard for a single detached dwelling
Setbacks match the standard for a single detached dwelling in that zone
Allowed zoning districts
One Accessory Dwelling is allowed per lot with an existing single detached dwelling, citywide, under Development Code Section 10.0100 - the same section that governs Gresham's low- and standard-density residential districts (including LDR-5, LDR-7, TR, and TLDR). Confirm your parcel's zoning with Gresham Urban Design & Planning.
Additional standards
Setbacks, parking & other rules
Setbacks
Freestanding ADUs: no closer to the street than the primary dwelling, 5 ft interior side, 10 ft rear (5 ft rear if the lot has an alley). Attached ADUs follow the same setback standard as a single detached dwelling in that zone
Parking
No additional off-street parking is required specifically for the ADU; Oregon state law bars cities from imposing this. The lot's base residential parking standard for the primary dwelling still applies
Units per lot
1 Accessory Dwelling permitted per existing primary single detached dwelling
Owner-occupancy
Not required, consistent with Oregon's HB 2001. The ADU simply cannot be occupied sooner than the primary dwelling
Building code
Must meet Oregon Residential Specialty Code dwelling-unit standards, plus Gresham's own sustainable-design menu - a cool ("white") roof on flat roofs, and at least one option from a list that includes minimum wall/ceiling insulation values, an EV charging provision, pervious paving with canopy trees, or a solar-ready roof zone
Rental license
A residential rental license is required to rent out the ADU; short-term rentals (B&B-style) are not allowed in ADUs
Ordinance history
How Gresham's ADU rules got here
2017Oregon's SB 1051 passes. The state's first statewide ADU mandate required cities with more than 2,500 residents, including Gresham, to allow at least one accessory dwelling unit per single-family lot.
2019Oregon passes HB 2001. Signed August 8, 2019, the law built on SB 1051 by barring cities statewide from imposing owner-occupancy or off-street parking requirements on ADUs, with compliance required by January 2020.
2025Oregon passes HB 2138. Signed by Governor Tina Kotek in July 2025, the law expands "middle housing" rules statewide - including ADUs - with a new density bonus for affordable and accessible units and a provision voiding older HOA covenants that try to block ADUs. Its main provisions become operative January 1, 2027.
Gresham, Oregon's fourth-largest city with a population above 110,000, implements these state mandates through Development Code Section 10.0100, which permits one Accessory Dwelling per lot through a single administrative Type I review - no public hearing required. That makes the zoning process itself fairly light-touch; Gresham's own sustainable-design requirements and standard System Development Charges are the more likely sources of added cost and complexity today.
Permit process
How Gresham ADU permitting works
1
Pre-application check
Confirm your zoning district and lot eligibility with the Planner on Duty before you design.
2
Prepare your plan set
Site plan, floor plans, and elevations for the ADU, plus floor plans of the existing house to verify the 900 sq ft / 75% size formula, and at least one sustainable-design option from the code's menu.
3
Submit your development permit application
File through Gresham's online portal with the ADU narrative statement form, site and floor plans, and the current application fee.
4
Type I review
The Manager reviews the application administratively under a Type I procedure - no public hearing is required for a compliant ADU.
5
Building permit & inspections
Once the Type I decision is issued, pull your building permit, begin construction, and schedule the standard framing, plumbing, electrical, and final inspections.
6
Rental license (if renting)
Apply for a residential rental license before placing tenants in the ADU. Short-term rentals are not allowed.
Fees and review timelines are set annually in Gresham's Master Fee Schedule and change periodically - confirm current figures with Urban Design & Planning before budgeting.
Budgeting
What it costs to build an ADU in Gresham
Garage conversion
Roughly $70,000-$170,000, the least expensive path since the shell already exists
Basement conversion
Roughly $100,000-$210,000, depending on existing ceiling height and utility access
New detached ADU
Roughly $150,000-$310,000+ for a code-compliant, fully insulated freestanding unit
Development permit application fee
A nonrefundable fee set in the city's current Master Fee Schedule, commonly a few hundred to a bit over a thousand dollars, separate from the building permit fee
System Development Charges (SDCs)
Transportation and Parks SDCs apply and can add several thousand dollars; get a project-specific estimate from Gresham's online SDC calculator before budgeting
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions, finishes, and which sustainable-design option you choose to satisfy the code's menu. Unlike Portland, Gresham does not currently offer an SDC waiver program for ADUs.
Before you apply
Tips for a smooth approval
Confirm your zoning district before you design. A quick pre-application check with the Planner on Duty avoids redesigning a project that doesn't fit your lot.
Double-check the size formula against your actual house. The 900 sq ft cap only applies if 75% of your home's floor area is larger - many homes are capped well below 900 sq ft.
Pick your sustainable-design option early. You only need to satisfy one item from the code's menu (extra insulation, EV charging, pervious paving with trees, or a solar-ready roof, among others), but it affects your floor plan and budget, so decide before your plans are finalized.
Budget for SDCs separately from your building permit. Transportation and Parks System Development Charges are billed apart from standard permit fees and are easy to underestimate.
Decide on rental plans before you build. A residential rental license is required to rent out the ADU, and short-term rentals aren't allowed at all - plan the layout with long-term rental in mind if that's the goal.
FAQ
Common questions
Do I need to live on the property to build an ADU in Gresham?
No. Oregon's HB 2001 (2019) bars cities from requiring owner-occupancy for ADUs, and Gresham's Development Code doesn't impose one. The only timing rule is that the ADU can't be occupied before the primary dwelling.
How many ADUs can I build on one lot?
One Accessory Dwelling is permitted per existing primary single detached dwelling.
Do I need extra parking for an ADU?
No. Oregon state law bars cities from requiring off-street parking specifically for an ADU, and Gresham doesn't impose one. The primary dwelling's own base parking standard still applies to the lot.
What's the maximum size for an ADU in Gresham?
900 sq ft or 75% of the primary dwelling's floor area, whichever is smaller. A freestanding ADU also can't exceed the height of the primary dwelling.
How long does the permit process take?
ADUs go through an administrative Type I review with no public hearing, which is generally faster than discretionary review - but timelines depend on application completeness and current staff workload. Confirm current timelines with Urban Design & Planning.
Does Gresham require any special "green building" features for an ADU?
Yes. Gresham's code requires a cool ("white") roof on flat roofs, and at least one item from a menu of sustainable-design options - extra insulation, an EV charging provision, pervious paving with canopy trees, or a solar-ready roof zone, among others.
How much does an ADU cost to build in Gresham?
Garage conversions tend to run roughly $70,000-$170,000, basement conversions $100,000-$210,000, and new detached units $150,000-$310,000 or more, based on local contractor estimates and regional reporting - not counting permit fees or System Development Charges.
Is Gresham subject to the same ADU rules as Portland?
Both cities operate under the same Oregon state laws (SB 1051, HB 2001, and HB 2138), but each sets its own local size, setback, and design standards. Gresham's 900 sq ft / 75% size cap and sustainable-design menu are distinct from Portland's own code.
Can I rent my ADU out on Airbnb or a short-term rental platform?
No. Gresham's Development Code specifically prohibits using an Accessory Dwelling as a short-term rental (B&B-style stays). Long-term rental is allowed once you obtain a residential rental license.
