Tree Protection During Construction: TPZ Planning for Kelowna Developers

If you are planning a construction or development project in Kelowna, understanding Tree Protection Zones is not optional. It is a municipal requirement. The City of Kelowna and surrounding municipalities mandate tree protection measures for any development that could impact existing trees, and failing to comply can result in project delays, fines, and costly remediation.

This guide explains what a TPZ is, how to calculate it, and what developers need to know to meet Kelowna's regulatory requirements while keeping their projects on schedule.

What Is a Tree Protection Zone?

A Tree Protection Zone is the designated area around a tree that must be protected from construction activity. The TPZ encompasses the critical root zone, which is the area where the majority of a tree's structural and absorptive roots are located. Damage to roots within this zone can compromise tree stability, reduce health, and ultimately lead to tree death.

The TPZ is not just about the trunk. Most of a tree's roots extend well beyond the canopy edge, and even minor soil disturbance within the critical root zone can cause significant long-term damage.

How to Calculate the TPZ

The standard method for calculating a TPZ is based on the tree's trunk diameter measured at 1.4 metres above ground level (diameter at breast height, or DBH). The general formula used in Kelowna follows the Australian Standard AS4970, which is widely adopted in British Columbia.

An ISA certified arborist may adjust the TPZ based on species, soil conditions, root architecture, and site-specific factors. Some species are more tolerant of root disturbance than others, and soil type significantly affects how far roots extend.

Municipal Requirements in Kelowna

The City of Kelowna requires a Tree Management Plan for most development applications where existing trees may be affected. This plan must include an arborist report, TPZ calculations, and a tree protection plan showing how trees will be safeguarded during construction.

• An arborist report assessing the health, condition, and retention value of all trees on site
• TPZ calculations for each tree proposed for retention
• A site plan showing TPZ boundaries, tree protection fencing locations, and construction zones
• Tree protection fencing specifications (typically chain-link or rigid panel fencing)
• Monitoring requirements during construction

Tree protection fencing must be installed before any site work begins and must remain in place until construction is complete. The city may require inspection by the project arborist at key stages of construction.

Best Practices for Developers

Successful tree protection starts early. Engaging an arborist at the site planning stage, before design work is finalized, gives you the best chance of designing around significant trees and avoiding costly redesigns later.

• Commission the arborist report early and share it with your design team before finalizing site plans
• Design building footprints and service routes to avoid TPZ encroachment where possible
• Designate specific access routes and material storage areas outside TPZs
• Brief all site workers on TPZ boundaries and prohibited activities within those zones
• Schedule regular arborist inspections throughout construction, not just at the start and end

Common Mistakes

Even well-intentioned developers can damage trees during construction. The most common mistakes are preventable with proper planning and site management.

• Soil compaction from heavy equipment. Even a single pass of a loaded truck within the TPZ can compact soil enough to restrict root growth for years.
• Grade changes within the TPZ. Adding or removing even 10 to 15 cm of soil over root zones can suffocate roots or expose them to damage.
• Storing materials within the TPZ. Stacking lumber, soil, or equipment on root zones causes compaction and can physically damage surface roots.
• Trenching through root zones. Linear excavation for utilities is one of the most damaging activities. Hand digging, air spading, or boring under roots are alternatives.

When to Hire an Arborist

You should engage an ISA certified arborist as early as the feasibility or due diligence stage of your project. If trees are present on a site you are considering developing, an early assessment will identify which trees can realistically be retained, which may need removal permits, and what protection measures the municipality will require.

An experienced arborist can also help you avoid surprises during the permitting process. Trees that appear healthy from the outside may have internal decay or structural issues that change their retention value, and an arborist can identify these issues before they become problems during construction.