Tree risk assessment in Washington and Oregon

What ISA TRAQ is

The International Society of Arboriculture describes TRAQ as a voluntary qualification that trains and assesses arborists in a specialized field. The prerequisite is an existing credential: ISA Certified Arborist, Board Certified Master Arborist, Certified Urban Forest Professional or an equivalent on ISA’s eligibility list. The program is a two-day course followed by a half-day of written and performance-based assessment, built on ISA’s Best Management Practices: Tree Risk Assessment, and it certifies that the holder is proficient in limited-visual and basic tree risk assessment as the BMP defines them. The qualification must be renewed every seven years by retraining and retesting.

Two things follow. A “certified arborist” is not automatically a risk assessor; TRAQ is the add-on. And the method is standardized, so two TRAQ arborists looking at the same Douglas fir should land on the same rating and show the same work. The ANSI A300 tree-care standards, published as one consolidated document since January 1, 2024, are the written standard the assessment should cite.

Level 1, 2 and 3 assessments

• Level 1, limited visual. A walk-by or drive-by of many trees from one side, looking for obvious defects: dead tops, large dead limbs, visible cracks, lean with lifted soil. It is how a city or an HOA screens a street or a campus. It does not produce a rating you would take a tree down on.
• Level 2, basic. The standard assessment for a homeowner’s tree: a 360-degree ground inspection of the roots, trunk and crown with simple tools, usually a mallet to sound the trunk for hollows, a probe for cavities and decay, and binoculars for the crown. The arborist identifies the targets, estimates likelihood and consequences, and writes it up. This is the level Seattle’s Basic Tree Risk Assessment Form is built on and the level TRAQ qualifies an arborist to perform.
• Level 3, advanced. Only when a Level 2 cannot answer the question: resistance drilling or sonic tomography to measure how much sound wood is left in a trunk, aerial inspection by climbing or drone, root-collar excavation, or a load test. It is ordered for a specific defect and priced separately. Alabama Cooperative Extension’s summary of the ISA levels adds that Level 3 is more costly and time-intensive, needs the client’s approval before it proceeds, and can include laboratory testing of tree and soil samples and aerial inspection from a crane.

If an assessor proposes a Level 3 on every tree, ask which defect it is meant to resolve.

Likelihood times consequences, in plain words

The ISA method rates risk in three steps, each on a scale, and combines them in a matrix:

1. Likelihood of failure of the tree or the part being assessed, within a stated time frame (one year is typical). A fir with a sound trunk and no root damage is improbable to fail; a bigleaf maple with a cavity through half its stem and a fresh crack is probable or imminent.
2. Likelihood of impact. If it fails, will it hit the target? A limb over a bedroom roof has a high likelihood of impact. The same limb over a back fence with a rarely used path has a low one. Targets are people, structures, vehicles and anything else of value, and how often they are there matters.
3. Consequences if it does hit: negligible, minor, significant or severe. A 4-in branch on a shed is minor; a 30-in trunk on an occupied bedroom is severe.

Steps one and two combine into a likelihood that the failure will impact a target; that result crosses with consequences to give the risk rating: low, moderate, high or extreme. The rating is what the mitigation hangs on. “High” on a dead top over the driveway usually means prune it; “extreme” on a cracked trunk over the house means act now. The ISA’s homeowner brochure on recognizing tree risk lists what the assessor is looking at: dead branches (“probably the most obvious potential hazards”), cracks and splits, codominant stems, decay signs such as fungal fruiting bodies and asymmetric swelling, soil cracks that suggest root movement, external wounds and cankers, poor taper, and damage from construction or past pruning.

Screening your own tree before you call

ISA’s homeowner brochure gives eleven yes-or-no questions. Paraphrased, they ask whether the tree has:

• large dead branches, or broken branches still hanging in the crown;
• dropped branches already;
• loose bark on the trunk, or cracks and splits in the trunk or where limbs attach;
• a trunk that has developed an unusual shape;
• cavities or rotten wood in the trunk or major limbs, or mushrooms at the base or under the canopy;
• had recent construction, a change in soil level, or new lawn or paving around it;
• leaves that are unusually yellow or smaller than normal;
• been topped or heavily pruned.

In ISA’s view one yes is enough to have an ISA Certified Arborist examine the tree. The same brochure’s hard rule: never try to remove branches or any tree part from or near power lines; if tree parts are touching a line, call your electric utility.

A second way to organize what you see comes from a Mississippi State University Extension publication (P3717, revised 2025). Its method, offered here as a general principle rather than a Washington or Oregon standard, scores three things from 1 to 4 and adds them: how likely the tree or limb is to fail, how big the failing part is, and how likely it is to hit a target. A total under 4 is low, 4 to 6 moderate, 7 to 9 high, and over 9 extreme. The size classes show why big Northwest conifers score high even with modest defects:

The same worksheet puts homeowner yards and trees close to houses or garages in its high target class, rates a standing dead tree high, and rates a dead tree with decay or cracks, or broken limbs hanging in the crown, extreme. Its failure thresholds give a sense of scale: decay across more than 40 percent of the trunk circumference, a lean beyond 40 degrees, or a hollow trunk with less than one-third of its thickness in sound wood each count as a high likelihood of failure. MSU also states that more than 80 percent of trees that fail in storms have defects. Treat a score as a reason to call, not a verdict: it is screening, not an assessment, and it does not replace the ISA matrix above.

Two more principles from public-agency guides. Alabama Cooperative Extension’s hazard-tree guide (FOR-2175, 2025) puts it plainly: without a potential target, a tree cannot qualify as a hazard, which is why a dead tree far from anything can be left standing as a wildlife snag. And the USDA Forest Service’s urban tree risk guide explains that canker-rot fungi, with Phellinus pini on conifers as its example, reinfect each new growth ring, so the tree cannot wall the decay off behind a solid shell of sound wood.

What the written report includes

A report you can use for a permit or an insurance file has the same parts whoever writes it:

• The tree: species, diameter at 4.5 ft, height, location on a sketch or site plan, and photos.
• The targets and how often they are occupied, and the time frame of the assessment.
• The defects observed, by part of the tree, with the method used (Level 2 or 3 and which tools).
• The three ratings and the combined risk rating for each part assessed.
• Mitigation options and the residual risk after each. The ISA brochure lists the usual menu: prune out the defective part, cable and brace, routine care, or remove when the risk is unacceptable; moving the target is the fifth option people forget.
• The assessor’s name, ISA certification number and TRAQ status, and a date; recommendations expire as trees change.

Lake Oswego’s code names the deliverable for a hazard-tree permit as a “Tree Risk Assessor Qualified Arborist report,” and Edmonds asks for a Tree Risk Assessment Form from an ISA Certified Arborist/Tree Risk Assessor before a hazard tree comes out (handout P46). Ask for the report in that form even where the city does not require it; it is what makes “dangerous” a finding instead of an opinion.

When Portland, Seattle and other cities require one

Other cities that ask for the document: Shoreline asks for a TRAQ arborist’s determination to remove a non-imminent hazard tree in a critical area (SMC 20.80.075(G)), and for its dead or imminent-hazard exemption the city checklist asks for an ISA tree risk assessment form from an ISA certified arborist (SMC 20.50.310); Lake Oswego may require a TRAQ arborist report for a hazard-tree permit and an arborist report for a dead-tree permit (LOC 55.02.042); Edmonds lets a hazard tree come out without a permit once it has reviewed a Tree Risk Assessment Form from an ISA Certified Arborist/Tree Risk Assessor, with a site plan and photos (handout P46); Kirkland requires an arborist report with any tree removal permit, including hazard claims (KZC 95.25); Bellevue still requires a clearing and grading permit, but a tree that a TRAQ-qualified tree professional rates hazardous (high or extreme risk) falls outside its annual removal limits and replanting rules (BCC 23.76.035; 23.76.060.G); Bremerton wants a certified arborist’s written determination for danger trees in critical areas (BMC 20.14.190). The lists are in tree removal permits in Washington and tree removal permits in Oregon.

Two situations where you want one even without a city rule: a tree leaning toward a neighbor’s house, where a dated report showing low risk, or showing that you acted on high risk, is your record if it later fails (Oregon neighbor tree law, Washington neighbor tree law); and a purchase, where a tree inspection before buying a home is a Level 1 of the lot and a Level 2 of anything over the roof.

What it costs

We do not publish a price for a risk assessment; there is no quote sample behind one and the work does not fit our crew-hour model. What you should expect is a flat fee quoted in advance for a stated number of trees at a stated level, with Level 3 instruments priced as a separate line. The only published figures are the cities’: Seattle charges 0.5 × its Land Use hourly rate to review a hazard-tree application and nothing for a dead tree, and Portland’s Urban Forestry hourly rate is $160 (FY2025-26) where its staff time is billed. Removal, when it follows, is priced on the tree removal cost page.

How to find a TRAQ-qualified arborist

1. Search the ISA directory at treesaregood.org/findanarborist and filter for the TRAQ credential, or verify a name at certificates.directory.isa-arbor.com. The directory is public and shows whether the credential is current.
2. Check the business license if the same company will do any work: in Oregon a CCB or LCB license is required for tree removal and pruning (Oregon lookup guide); in Washington, L&I contractor registration (Washington lookup guide). In Seattle, confirm the SDCI tree service provider registration.
3. Ask for a sample report, the level proposed for each tree, the time frame, and the fee in writing.

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