What happens if you skip the permit (and you needed one)
- Stop-work order + $500–$2,500 civil penalty per day of unpermitted work; Gresham code enforcement will post your job if a neighbor reports or if you pull utility permits without building permits.
- Insurance claim denial — your homeowner policy will not cover an unpermitted ADU if there's a fire, injury, or theft; lender or insurer discovery during refinance kills the deal.
- Title cloud + appraisal hit — when you sell, the buyer's appraiser will flag the ADU as 'non-permitted structure'; title company may require removal or $10K–$30K holdback, or deal dies.
- Forced removal or retrofit — if building department requires post-hoc compliance, you're reworking the unit to meet current code (foundation upgrades, egress windows, sprinklers) at 2–3x original cost.
Gresham ADU permits — the key details
Oregon state law is the floor, and Gresham leans into it hard. ORS 197.303 requires cities to allow one ADU per single-family lot with minimal restrictions; ORS 197.312 requires cities to allow 'internal' ADUs (junior ADUs carved out of the primary home) with even fewer restrictions. Gresham's code (GMC 26.64) adopts both and adds a ministerial ('shall approve') standard for compliant projects, meaning the planning director cannot invoke discretion — if your ADU meets the setback, size, and utility checklist, you get approval within 35 calendar days. This is a hard deadline; if Gresham misses it, your ADU is 'deemed approved' under state law. That said, the 35 days is for planning sign-off only; the full permit (including building review and inspections) typically runs 8–12 weeks from submission to ready-for-construction. The key code section is GMC 26.64.010–.050. Unlike some Oregon cities that cap ADU size at 600 or 800 square feet, Gresham allows up to 75% of the primary dwelling unit's size or 1,000 square feet, whichever is smaller — a generous threshold that lets you build a real 2-bedroom ADU on most lots.
Setback and lot-size rules are where most Gresham ADU projects choke. Detached ADUs must maintain 5 feet from side and rear property lines (front setback is 20 feet, matching the primary dwelling minimum). On a typical 6,000–8,000 square foot Gresham lot, a 600-square-foot detached ADU (roughly 24x25 feet) will squeeze through if your lot is wider than 50 feet; narrower or deeper lots force a garage conversion or attached unit instead. Attached ADUs (built onto the primary home) have no side-setback penalty but must share a wall with the primary dwelling — you cannot build a standalone building attached only by a breezeway or utility tunnel. Junior ADUs (carved from the existing primary home; think of a guest suite with its own kitchen and entrance within the same building envelope) have no setback issues but trigger sprinkler requirements if the total floor area of both dwellings exceeds 5,000 square feet. Gresham requires sprinklers in any ADU (attached or detached) with more than one bedroom, or in any ADU in a total structure exceeding 5,000 square feet. This rule is stricter than some Oregon suburbs and catches many applicants off guard — a 750-square-foot, 2-bedroom detached ADU on a lot with a 3,500-square-foot primary home will require a fire-sprinkler system. Budget $3,000–$8,000 for sprinklers if you're in this category.
Utility infrastructure is your second biggest filter. Gresham requires all ADUs to have independent utilities (separate water meter, sewer connection, electrical service, gas if applicable) — no master-metering or sub-metering to the primary dwelling. For a detached ADU, this means running new lines from the street; for an attached or junior ADU, you must install a sub-meter or demonstrably separate the utilities at the point of entry. If your lot cannot accommodate a new sewer tie-in (e.g., sewer main is on the far side of the primary home, or lot depth is < 60 feet), you may be forced into a junior ADU instead. Water service is usually simpler — most Gresham lots have capacity for a second meter — but check with Gresham Water & Electric before you buy the lot. Electrical is often the easiest, though Pacific Power may require a service upgrade if your primary panel is under-sized. Do not assume your existing utilities can handle a second dwelling; get a utility pre-check from Gresham Public Utilities and Pacific Power BEFORE committing design. Cost: $2,000–$5,000 for utility design and connection fees, on top of permit.
Owner-builder eligibility and the occupancy question. Gresham allows owner-builders to pull permits for ADUs if the primary residence is owner-occupied (you must live in the primary dwelling for at least 1 year post-ADU completion). This is permissive compared to some jurisdictions that ban owner-builders entirely for ADUs. The state law (ORS 197.303) forbids Gresham from requiring that you occupy the ADU itself — meaning you can build an ADU and rent it out from day one without owner-occupancy restrictions. However, you still cannot be an absentee landlord on the primary dwelling; you must own and occupy the main house. Rental income does not affect your permit eligibility in Gresham, and there are no local rent-control or deed-restriction requirements. If you plan to rent the ADU, note that Gresham's property-tax assessment may increase slightly (Multnomah County Assessor may re-value the lot as a duplex rather than a single-family home), but Oregon's Measure 50 cap limits the annual increase. Consult a tax professional if you're concerned, but do not let tax fear block your permit — it's a long-term economics question, not a permit question.
Plan review and inspection workflow. Submit your application to the Gresham Planning & Building Department online via the Gresham permitting portal (available at gresham-or.gov, under 'Services > Building Permits'). You will need: site plan (showing setbacks, lot coverage, parking), floor plans and elevations, structural details (foundation, framing), mechanical/electrical/plumbing (MEP) plans, and a completed ADU checklist (Form ADU-1, available on the city website). Plan review is free (included in permit fee); building review is included in the permit fee as well. Once you receive plan approval from planning (typically 35 days), you will receive a building permit and can begin construction. Inspections are standard: foundation, framing, rough (MEP), insulation/drywall, and final. Sprinklers (if required) have their own inspection. Each inspection usually passes same-day or next day if you've built to plan. Total permit timeline from submission to first inspection: 8–12 weeks. Total construction timeline (assuming decent weather and no rework): 4–8 months for a detached ADU.
Three Gresham accessory dwelling unit (adu) scenarios
Gresham's 35-day ministerial approval timeline — how it works and why it matters
Oregon state law (ORS 197.303 and 197.312) requires cities to approve ADUs 'ministerially' if they comply with local code criteria — meaning the city cannot deny your project based on discretion, neighbors, or policy disagreement, only on code compliance. Gresham was one of the first Portland-area cities to codify this (GMC 26.64, adopted 2018), and it sets a 35-calendar-day review window. If the planning director has not issued a decision by day 35, your ADU is 'deemed approved' under state law; you can appeal to the city manager or state land-use board if the delay is deliberate. In practice, Gresham's planning staff approve ADU applications within 20–30 days if the checklist is complete. This is a massive advantage over cities like Lake Oswego or West Linn that require a conditional-use permit or design review (60–120 days), or over Portland which expanded its ADU rules but still requires discretionary review for some configurations.
The key is a clean submission. Gresham provides Form ADU-1 (available on gresham-or.gov, under 'ADU Checklist'), which lists the exact criteria: lot size minimum (none — ORS 197.303 forbids this), setbacks (5 feet side/rear for detached), size cap (75% primary or 1,000 sq ft), utilities (separate or sub-metered), parking (not required per state law), and owner-occupancy (not required per state law; rental is OK). If your application includes a completed checklist, site plan, and floor plans, planning staff will either approve you or issue a 'Request for Information' (RFI) asking for clarifications (e.g., 'show utilities plan', 'clarify egress window location'). The 35 days pauses during the RFI period; once you respond, the clock resumes. Total elapsed time (including RFI back-and-forth) is usually 45–60 days. Building review (separate from planning) happens after planning approval and typically takes another 30–60 days.
Because Gresham's threshold is ministerial (not discretionary), you cannot be denied for aesthetic reasons, neighbor objections, or parking concerns — even if the neighbors send 20 letters to the city. The only ground for denial is code non-compliance. This shifts power away from the planning commission (which votes on discretionary cases) and toward the code itself. In practice, it means ADU applicants save money on legal representation; you don't need a planner or attorney to argue your case before a board — you just need to submit a clean application that checks the GMC 26.64 boxes.
Sprinkler requirements, frost depth, and climate — why Gresham's rules vary east to west
Gresham straddles two distinct climate zones: the Willamette Valley floor (4C, 12-inch frost depth, soft volcanic soils) in the west, and the foothills (5B, 30-inch frost depth, more clay and expansive soils) in the east. This matters for ADU design and cost. West Gresham (Centennial, Springwater) sits on alluvial bottomland; frost is shallow and soil is stable. East Gresham (Troutdale, Oxbow) sits on volcanic foothills with deeper frost and more expansive clay. The International Building Code (IBC Table 301.2[1]) requires frost footings below the frost-line depth, and Gresham enforces this via the Oregon Structural Specialty Code (OSSC), which adopts the IBC. If you are building a detached ADU in Troutdale (east), your foundation engineer will specify a footing 30 inches deep or deeper; in Centennial (west), 12 inches. Cost difference: East Gresham foundation is typically $2,000–$4,000 more expensive for the same footprint.
Sprinkler requirements layer on top of this. Gresham's fire-sprinkler rule (GMC 26.64.045) requires sprinklers in any ADU with more than one bedroom, OR in any structure (primary + ADU combined) exceeding 5,000 sq ft. The rule is not tied to climate, but the effect is that many Gresham lots (7,500–10,000 sq ft is common) will trigger sprinklers if you build even a modest 2-bedroom ADU. West Gresham, with shallower frost and cheaper site work, often offsets sprinkler costs with savings elsewhere; East Gresham, with deep frost and expensive site work, makes sprinklers the straw that breaks the budget. Budget $6,000–$12,000 for sprinklers in a new detached ADU; $2,000–$4,000 if you're retrofitting (adding to existing main structure or converting garage).
Soil is a secondary but real factor. Volcanic soils (common in East Gresham) are often expansive or poorly draining; if your site has a high water table or seasonal flooding (the Oxbow area sits near Beaver Creek), you may be required to install perimeter French drains or a sump pump. Multnomah County Soil Survey (free, online) maps expansive-clay areas; if your lot is flagged, add another $1,500–$3,000 for drainage design. West Gresham (Willamette Valley floor) rarely has these issues. Neither rule is new, but they hit ADU budgets harder than primary-home budgets because ADU projects are tighter on margin; a $200K primary home can absorb a $4K drainage surprise, but a $150K detached ADU cannot.
1333 NW Eastman Parkway, Gresham, OR 97030 (City Hall main line; ask for Building Permits)
Phone: 503-618-2496 (Planning) or 503-618-2557 (Building; verify locally as numbers may change) | https://www.gresham-or.gov/Services/Building-Permits or search 'Gresham OR permit portal'
Monday–Friday, 8:00 AM–5:00 PM (closed weekends and city holidays; call ahead to confirm)
Common questions
Can I build a detached ADU if my lot is only 40 feet wide?
No. Gresham requires 5-foot setbacks from side property lines for a detached ADU, so a 40-foot lot leaves only 30 feet of usable width — too narrow for a livable 20+ foot-wide building. Your options are a junior ADU (interior carve-out), attached ADU (sharing a wall with primary), or garage conversion. If you choose a garage conversion, the existing garage does not have to meet the new 5-foot setback (pre-existing non-conforming), but the converted space must still meet foundation, egress, and utility code.
Do I have to own and live in the primary home to get an ADU permit in Gresham?
Yes for owner-builder eligibility: you must own and live in the primary residence for at least 1 year post-completion. However, you do NOT have to live in the ADU itself, and Oregon state law (ORS 197.303) forbids Gresham from requiring ADU owner-occupancy. You can rent out the ADU from day one. If you are a licensed contractor (not an owner-builder), the primary-home occupancy rule may vary — contact the building department to confirm.
What if my lot does not have room for separate sewer and water connections?
Gresham allows sub-metering for attached and junior ADUs: you can install a dedicated water/sewer sub-meter at the main point of entry and bill the ADU tenant separately. For detached ADUs, separate connections are strongly preferred, but if the lot is too tight or sewer is unavailable, contact the building department to discuss alternatives. In rare cases, wastewater treatment (greywater system) may be approved, but this requires additional design review and environmental clearance.
Do I need parking for an ADU in Gresham?
No. Oregon state law (ORS 197.303) forbids cities from requiring off-street parking for ADUs. Gresham does not require a parking space for the ADU itself, on-site or off-site. However, local street parking rules still apply; if you are on a narrow residential street, ensure adequate curb space for visitors.
How much does a Gresham ADU permit cost?
Typically $3,500–$6,000 total (permit, plan review, and building review combined), based on 1.5% of the estimated construction valuation plus fixed fees. A $150K ADU = ~$2,250 valuation fee + $800 plan-review + $1,200 inspection contingency = ~$4,250. Add $800–$1,500 if a conditional-use permit (rare) or historic-district review is required. Sprinkler inspection is ~$1,200 additional if sprinklers are triggered.
Can I pull a permit for an ADU myself, or do I need a contractor or planner?
You can pull the permit yourself if you are an owner-builder (primary residence owner-occupied). Gresham does not require you to hire a planner or permit expediter. However, you will need to prepare site plans, floor plans, and MEP drawings (these require a designer or architect if you lack CAD skills). Many owner-builders hire a draftsperson (~$1,500–$3,000) to draw plans from their sketch, then submit themselves. If you hire a licensed contractor, they will typically handle permitting.
What is the difference between a junior ADU and an attached ADU in Gresham?
A junior ADU is carved from inside the primary dwelling (e.g., basement, attic, or converted garage integrated into the home's footprint); it shares utilities and does not add new square footage to the lot. An attached ADU is a new addition built onto the side or rear of the primary home, sharing only a wall but with separate utilities. Junior ADUs are faster to permit (no new foundation required), cheaper (existing structure), and do not trigger sprinklers if under 500 sq ft. Attached ADUs are slower (foundation, full MEP design) but allow more flexibility in layout and size.
How long does it take to get a Gresham ADU permit from start to first inspection?
Typically 8–12 weeks: 35 days planning approval (ministerial review) + 30–60 days building review + 2–4 weeks for staff to issue the final permit and schedule first inspection. If you have a complete application, no RFI back-and-forth, and no sprinkler or foundation questions, you can compress this to 6–8 weeks. Construction itself (foundation through final) typically runs 4–8 months for a detached ADU, depending on weather and rework.
Do I need sprinklers in my ADU?
Yes if: (1) your ADU has 2+ bedrooms, OR (2) the combined floor area of the primary home + ADU exceeds 5,000 sq ft. A 750 sq ft, 2-bedroom ADU on a lot with a 3,200 sq ft primary home will require sprinklers (condition 1), even though the total is only 3,950 sq ft. A 550 sq ft, 1-bedroom junior ADU on the same lot will not require sprinklers. Budget $6,000–$12,000 for sprinklers if required; this is often the second-largest cost after construction.
What happens if Gresham misses the 35-day deadline for ADU approval?
Your ADU is 'deemed approved' under ORS 197.303. You can request written confirmation of the approval from the planning director, then proceed to building review. You cannot be forced to re-apply or wait longer. In practice, Gresham planners are aware of the deadline and avoid missing it; if you sense a delay, contact the planning director and reference ORS 197.303.