Planning to build an ADU in Portland? An accessory dwelling unit can add flexible living space, rental potential, or room for family. But before the project can move forward, the permit review needs clear drawings. One of the most important drawings is the ADU site plan.
A site plan shows the property from above. For a Portland ADU project, it helps reviewers understand where the ADU will sit, how close it is to property lines, how it relates to the existing house, whether trees or easements are affected, and how drainage, access, and utilities may be handled.
A good site plan does not just show a box labelled “ADU.” It explains the whole site clearly enough for permit review.
Need a Portland ADU Site Plan?
Order a clear permit site plan showing your proposed ADU, existing house, property lines, setbacks, access, trees, easements, utilities and other important site details.
Does an ADU Need a Permit in Portland?
Yes. Portland’s Accessory Dwelling Unit guidance says you need a building permit to build a new ADU. A building permit is also required if you are converting an attic, basement, or garage into living or habitable space.
Depending on the project, you may also need trade permits for electrical, plumbing, mechanical, or other work. A detached ADU, garage conversion, basement conversion, or attached ADU can each raise different site and building-code questions.
Portland also offers pre-approved detached ADU plans, which can help some homeowners save time during the building permit process. Even with pre-approved plans, the ADU still needs to fit correctly on your specific property.
For a broader overview of residential ADU drawing requirements, read our guide on whether you need a site plan for an ADU permit.
What Is a Portland ADU Site Plan?
A Portland ADU site plan is a scaled drawing of the property. It shows existing conditions and proposed work from a top-down view.
For an ADU, the site plan may show:
- Property lines
- Lot dimensions
- Existing house
- Existing garage, shed, driveway, paths, and other structures
- Proposed ADU footprint
- Setbacks from property lines
- Distance from the ADU to the existing house
- Street frontage and access
- Easements
- Trees and vegetation
- Utilities and meters
- Drainage direction or stormwater features
- North arrow and scale
Portland’s site plan guidance says site plans must be drawn on an 11-inch by 17-inch or larger sheet, and all permit drawings should be the same sheet size. The city also expects the drawing to be to scale.
Homeowners can also use our permit site plan checklist to review the basic property and project details commonly requested before submission.
Why the Site Plan Matters for ADU Permit Review
An ADU is reviewed as both a building and a site improvement. Reviewers need to understand the structure itself, but they also need to see how it fits on the lot.
A clear ADU site plan helps answer questions like:
- Is the ADU allowed on this property?
- Where is the ADU located?
- How large is the ADU footprint?
- Does it meet setbacks?
- Does it affect existing trees?
- Does it affect drainage or stormwater management?
- Are easements or utilities in the way?
- How does the ADU relate to the existing house, garage, driveway, and street?
If the site plan is unclear, the review can slow down because the city may need corrections or more information. Our guide explaining what permit reviewers check first on a site plan covers the information that should be easy to find at a glance.
What Homeowners Need to Show on a Portland ADU Site Plan
1. Property Lines and Lot Dimensions
Start with the property boundaries. These lines show the legal edges of the lot and help reviewers understand the ADU’s placement.
Your site plan should show:
- Front property line
- Side property lines
- Rear property line
- Lot width and depth, if available
- Any irregular lot shape
Property lines are the reference point for setbacks, easements, lot coverage, and building placement. If they are missing or unclear, the ADU review can get stuck early.
A drafted site plan is not the same as a licensed boundary survey. Our guide comparing a site plan and survey explains when verified boundary information may be required.
2. Existing House and Structures
The existing home should be clearly shown and labelled. The plan should also show any other major structures or improvements on the lot.
Common existing features include:
- Main house
- Garage
- Shed
- Deck or patio
- Driveway
- Walkways
- Retaining walls
- Fences, if relevant
This helps reviewers understand the current site before looking at the proposed ADU.
3. Proposed ADU Footprint
The proposed ADU should be clearly shown and labelled. Use a label such as “Proposed ADU” so there is no confusion.
Show the ADU’s:
- Length
- Width
- Footprint area
- Location on the lot
- Relationship to the existing house
- Relationship to the garage, driveway, trees, or easements
If the ADU is a garage conversion or basement conversion, the site plan should still show the existing structure and clearly identify the conversion area.
4. Setback Distances
Setbacks are one of the most important parts of an ADU site plan. They show how far the proposed ADU is from the property lines and other structures.
Your site plan should include:
- Distance from ADU to rear property line
- Distance from ADU to side property lines
- Distance from ADU to the existing house
- Distance from ADU to other structures, if relevant
- Distance from roof overhangs or projections to property lines, if close
Portland’s ADU zoning requirements depend on the property’s zoning and site conditions. The city’s ADU zoning page explains that ADUs are allowed on sites with a house, attached house, or manufactured home, but minimum lot-size and other requirements vary depending on the zone and number of ADUs.
5. Trees and Vegetation
Trees can be a major issue for ADU placement in Portland. If the ADU is near existing trees, the site plan should show them clearly.
Your site plan may need to show:
- Existing trees
- Tree diameter, if known
- Trees near the proposed ADU
- Trees near driveway or utility work
- Trees proposed to remain
- Trees proposed for removal, if applicable
Even if the ADU structure fits within the setbacks, tree protection or removal requirements can affect where it can be built. This is exactly the kind of detail that can surprise homeowners late in the process. Tiny tree icon on the plan now, fewer permit gremlins later.
6. Easements
Easements are another common ADU site-plan issue. Utility, drainage, or access easements can limit where an ADU can be placed.
Show known easements, such as:
- Utility easements
- Drainage easements
- Access easements
- Sewer or water easements
- Shared driveway or access areas
If you have a survey, deed, title report, or previous site plan showing easements, use that information before finalizing the ADU location.
7. Drainage and Stormwater
An ADU adds roof area and may add walkways, patios, or driveway surfaces. That can affect stormwater management.
Your site plan should show drainage-related details when relevant, such as:
- Drainage direction
- Existing slopes
- Downspout locations
- Stormwater planters or facilities, if proposed
- Pervious surfaces
- New paved areas
- Drainage easements
Drainage details matter because new roofs and paving can change how water moves across the site. Reviewers may need to understand whether the ADU creates new runoff or affects neighboring properties.
8. Access and Walkways
The site plan should show how people will access the ADU. This is especially important for detached ADUs in the rear yard, garage conversions, and lots with narrow side yards.
Show access features such as:
- Walkway from street or driveway
- Side yard access
- Driveway
- Alley access, if present
- Entry door location, if helpful
- Accessible path details, if required
Reviewers should be able to understand how the ADU connects to the rest of the property.
Where the project changes a driveway or parking area, our guides on driveway permit site plans and driveway widening permit requirements may also be useful.
9. Utilities and Service Connections
ADUs often involve utility work. Depending on the design, the ADU may need electrical, plumbing, water, sewer, or mechanical connections.
Your site plan may need to show:
- Water meter
- Electric meter or panel
- Gas meter, if relevant
- Sewer line, if known
- Water service line, if known
- Utility trenching route, if relevant
- Mechanical equipment location
Even when full utility plans are separate, the site plan should not ignore obvious utility conflicts.
Have Your Portland ADU Information Ready?
Send your available survey, parcel information, ADU dimensions, preferred location, photographs and permit requirements. Site Plan Pros can organize the details into a clean permit-focused site plan.
10. Street Frontage, Alley, and Orientation
A good ADU site plan should help reviewers orient the property quickly.
Include:
- Street frontage
- Alley, if present
- Driveway
- North arrow
- Scale
- Property address
These basics make the plan easier to review and reduce confusion, especially on corner lots, alley lots, and irregular lots.
Detached ADU vs Attached ADU vs Conversion
Detached ADU
A detached ADU is separate from the main house. The site plan should focus heavily on location, setbacks, distance to the house, trees, stormwater, access, and utilities.
If the detached ADU is built near or replaces a garage, our guide on garage permit site plans provides related information about setbacks, driveway access and building separation.
Attached ADU
An attached ADU connects to the existing house. The site plan should show the expanded building footprint and how the addition affects setbacks, lot coverage, drainage, and existing site features.
Attached ADUs share several site-plan issues with conventional additions. Read our guide on home addition permit site plans for more information about new footprints, setbacks and lot coverage.
Garage, Basement, or Attic Conversion
For a conversion, the building footprint may not change much, but the permit still needs to show the property context. The site plan should identify the existing structure and where the ADU conversion is located.
Common Portland ADU Site Plan Mistakes
Many review delays come from missing or unclear site plan details. Common issues include:
- No property lines shown
- No lot dimensions
- ADU footprint not clearly labelled
- Setback distances missing
- Existing house not shown clearly
- Garage, shed, or driveway missing
- Trees not shown
- Easements missing
- Drainage direction not shown
- Utilities ignored
- Access path unclear
- No north arrow or scale
- Drawing is too small, blurry, or not on the correct sheet size
Our article explaining why site plans get rejected or delayed covers common correction requests and missing information in greater detail.
Portland Site Plan Format Basics
Portland’s site plan guidance says the site plan must be drawn on an 11-inch by 17-inch or larger sheet. It also says all permit drawings should be the same sheet size.
For a smoother review, make sure your ADU site plan is:
- Drawn to scale
- Readable on the uploaded PDF
- Clearly labelled
- Consistent with other drawings
- Large enough for reviewers to read dimensions
- Not cropped or blurry
Can You Use an Old Survey?
An old survey can be a helpful starting point if it shows property lines, easements, structures, and lot dimensions. But it usually will not show the proposed ADU.
For permit review, the ADU footprint, setbacks, access, trees, utilities, and drainage details should be added clearly. If the survey is outdated or missing current structures, the site plan may need to be updated.
Can You Use an Online Map Screenshot?
An online map screenshot can help you understand the property, but it is usually not enough for a permit-ready ADU site plan. Aerial images can be outdated, distorted, missing exact property lines, and missing dimensions.
A better ADU site plan should be scaled, labelled, and specific to the permit review.
Simple Portland ADU Site Plan Checklist
Before submitting your ADU permit materials, check that your site plan includes:
- Property lines
- Lot dimensions
- Existing house
- Existing garage, shed, driveway, paths, or other structures
- Proposed ADU footprint
- ADU length and width
- Setback distances
- Distance from ADU to existing house
- Trees and vegetation, where relevant
- Easements
- Drainage direction or stormwater features
- Access path to the ADU
- Utilities and meters, if relevant
- Street frontage or alley
- North arrow and scale
- Clear labels for existing and proposed features
Need a Portland ADU Site Plan?
If you are planning an ADU in Portland, a clear site plan can help show reviewers what they need to see before approval. It can show the proposed ADU, existing house, property lines, setbacks, trees, easements, drainage direction, utilities, access, and other important site details.
Site Plan Pros prepares easy-to-read site plans and plot plans for residential permit applications, including ADUs, additions, garages, decks, pools, patios, sheds, fences, carports, driveways, and other homeowner projects.
Whether you are building a detached ADU, converting a garage, creating a basement unit, or preparing documents for your designer or contractor, a clean site plan can reduce confusion and support a smoother permit review.
Show the layout clearly before the review starts.
Ready to Order Your Portland ADU Site Plan?
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