What an Arborist Report Includes and When the City Requires One

Property owners on the San Francisco Peninsula are typically required to obtain a formal arborist report in four common scenarios:

1. Protected Tree Removal Applications: Under Redwood City Municipal Code Chapter 29 and San Mateo County Significant Tree Ordinances, removing any tree over designated diameter thresholds (12 inches DBH in Redwood City; 55 inches circumference in county areas) requires an arborist report documenting why removal is justified based on severe disease, structural hazard, or infrastructure damage. 2. Residential Construction & Remodeling Permits: When applying for building permits for home additions, swimming pools, detached ADUs, or driveways, cities require a Tree Protection Plan (TPP) to safeguard existing mature trees within the construction zone. 3. Insurance Damage Claims: Following a winter storm tree strike, insurance adjusters frequently demand an arborist report to verify tree health prior to the storm and establish that the incident was an unforeseen 'Act of God' rather than deferred maintenance. 4. Boundary Line Neighbor Disputes: Resolving conflicts over root damage to retaining walls, foundations, or encroaching canopy risk under California Civil Code § 1714.

To be accepted by municipal urban forestry staff, an arborist report must follow strict ISA guidelines and include comprehensive data:

• Precise Taxonomic & Physical Identification: Botanical species name, common name, GPS coordinates, and exact diameter at breast height (DBH measured 54 inches above natural grade). • Canopy & Structural Health Assessment: Crown vigor rating (1 to 5 scale), percentage of live crown ratio, leaf color, presence of epicormic sprouting, and canopy dieback measurements. • Structural Defect Analysis: Detailed documentation of codominant stems, included bark, basal trunk cavities, cracks, lightning strikes, and fungal conks indicating internal heartwood decay. • ISA TRAQ Risk Rating Matrix: Objective risk rating combining likelihood of failure, likelihood of impacting a target (home, driveway, public street), and consequences of failure (negligible to severe). • Diagnostic Testing Data: When visual assessments are inconclusive, reports may include data from sonic tomography (sound-wave decay mapping) or resistograph micro-drill resistance testing. • Actionable Recommendations & Mitigation Plan: Specific prescriptions (crown thinning, cabling, soil aeration) or justification for removal, accompanied by a tree replacement schedule specifying native container species.

When building on parcels with mature heritage trees, cities mandate a comprehensive Tree Protection Plan (TPP) integrated into the civil engineering architectural drawings. The report establishes critical protection parameters:

• Critical Root Zone (CRZ) & Tree Protection Zone (TPZ): Calculated as one foot of radial protection for every inch of trunk DBH. A 24-inch coast live oak requires a mandatory 24-foot radius protective zone surrounding the trunk. • Tree Protection Fencing Specifications: Requirements for 6-foot galvanized chain-link fencing anchored with steel posts driven into the ground, barring heavy machinery, soil grading, or material stockpiling inside the dripline. • Specialized Root Pruning & Pneumatic AirSpade Work: Prescribing AirSpade supersonic air trenching to expose tree roots without tearing bark when utility trenches must cross the root zone.

The investment for an ISA Arborist Report depends on the scope of the project:

• Single-Tree Permit Application Report: Typically ranges between $350 and $650 for a standard residential tree hazard assessment in Redwood City or Menlo Park, including on-site inspection, photographic documentation, and report preparation. • Multi-Tree Inventory & Construction Impact Plan: Ranges from $1,200 to $3,500+ for residential development sites involving 5 to 20 mature trees, detailed CAD-ready mapping, and ongoing construction monitoring visits. • Standard Turnaround Time: Most reports are delivered within 3 to 5 business days following the on-site physical evaluation. Expedited 24-hour turnaround is available for urgent real estate escrow or active building permit deadlines.

Municipal planning commissions and city foresters reject poorly prepared arborist reports that read like biased sales pitches from tree cutting companies. To guarantee permit approval, reports must demonstrate strict adherence to ISA ethical standards and municipal codes.

Our ISA Certified Arborists maintain deep familiarity with the specific requirements of Redwood City, San Carlos, Menlo Park, Atherton, and San Mateo planning departments. We provide unbiased, scientifically rigorous reports that city planners respect and approve without contentious revisions.