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Gresham, OR Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Gresham, OR, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Units allowed: One ADU per single detached dwelling
Size cap: 900 sq ft or 75% of primary
Review track: Type I administrative application
Density: Doesn't count toward most density limits

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Oregon under recent ADU streamlining laws. The Gresham, OR rules below cover local size, height, and setback requirements.

Summary

Gresham allows one Accessory Dwelling per single detached dwelling, capped at 900 square feet or 75 percent of the primary home's floor area, whichever is smaller, under Development Code Section 10.0110.

The purpose of this section is to allow for establishment of an Accessory Dwelling in conjunction with a single detached dwelling. An Accessory Dwelling may be permitted as a means of providing more housing opportunities... The Manager shall approve an application for not more than one Accessory Dwelling per existing primary single detached dwelling if the applicant shows compliance with the following standards... F. Accessory Dwellings shall have a maximum floor area of 900 square feet or 75 percent of the floor area of the primary dwelling, whichever is less.

View official code

Full Breakdown

Development Code Section 10.0101 lets a single detached dwelling add one Accessory Dwelling, attached or freestanding, to expand housing options without counting toward density limits in most residential districts. Section 10.0110 caps floor area at 900 square feet or 75 percent of the primary dwelling's size, whichever is less, and requires the ADU to match the primary home's height and lot-coverage limits, plus setbacks that depend on whether it is attached or freestanding.

Violations & Fines

Applications that miss the standards in Section 10.0110 don't get administrative approval: the applicant must instead pursue Variance review under Section 10.1500 before building.

Frequently Asked Questions

Can I build more than one ADU in Gresham?

No. The Development Code allows only one Accessory Dwelling per existing primary single detached dwelling, per Section 10.0110.

How big can a Gresham accessory dwelling be?

Up to 900 square feet, or 75 percent of the primary home's floor area: whichever number is smaller.

Sources & Official References

[1]Gresham Community Development Code

Other rules in Gresham

Fence Regulations: Height LimitsSome Restrictions Shed & Carport RulesSome Restrictions ADU Rental RestrictionsHeavy Restrictions Noise Ordinances: Aircraft NoiseSignificant Restrictions Parking Rules: EV ChargingLight Restrictions Parking Rules: Loading ZonesSome Restrictions Fence Regulations: Material RestrictionsSome Restrictions Fire Regulations: Smoke DetectorsSome Restrictions

All Gresham rules

How Gresham compares: Easiest Cities to Build an ADU·Compare Gresham to another location·View the Oregon accessory structures overview

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ADU Rules in Nearby Cities

How other cities in Multnomah County handle adu rules.

Portland, OR