Walk the lot for protected trees

The rules in plain language

Portland City Code Title 11 governs trees on private property. For a DADU, the chapter that applies is Chapter 11.50 — Trees in Development Situations, which kicks in at 12 inches diameter at breast height (DBH) on the development site (§ 11.50.040). Trees 20" DBH or larger must be preserved unless an exemption applies (§ 11.50.040.C). A DADU permit triggers a Title 11 review that looks at every tree on your lot and the root protection zones of trees on the neighbors'.

In plain language:

• A tree plan goes in with the permit (§ 11.50.020).
• Removing a regulated tree means preservation, on-site planting, or a fee-in-lieu — pick one.
• The root protection zone (typically 1 foot of radius per inch of DBH) has to be respected during construction. Foundation work inside the RPZ usually kills the tree and creates a code enforcement problem.
• Outside development, removing trees ≥6" DBH falls under Chapter 11.40 — different process. For a DADU, 11.50 is what binds.

How to do the DIY walk

1. Take a measuring tape around the lot. For every tree on your lot or close to a lot line, measure DBH at 4.5 ft above grade.
2. Sketch a rough site plan with tree locations.
3. Anything ≥12" DBH gets flagged for the Title 11.50 review; anything ≥20" is presumptively preserved.
4. If a 12"+ tree sits near your planned footprint, bring in an ISA-certified arborist before you commit to design.

When to hire an arborist now instead of later

At feasibility — not at permit — if:

• A tree ≥12" DBH sits within 30 feet of your proposed footprint.
• You can't tell whether a tree is on your lot or the neighbor's.
• The tree looks stressed or has visible decay (an arborist's report can let you remove a hazard tree without mitigation).

Permit-stage tree work runs $1,500-$3,500. A feasibility-stage consult is $400-$800 and often gives you a yes/no in an afternoon.