Before Construction: Design for Tree Survival


Figure 1
The Critical Root Zone (CRZ)

Pick the trees to save and design the house to accommodate them. Look for healthy trees of desirable species. Pay special attention to shade potential for the house and nearby cement/asphalt areas.

Determine the Critical Root Zone (CRZ) for each tree, which is roughly a circle with a radius equal to the average

dripline(see Figure 1). Realize that most tree roots are in the top two feet of soil, and that feed roots are in the top few inches (see Figure 2). Roots require non-compacted soil for both air and moisture.

Protect at 75% of the CRZ. Fence the are to prevent traffic or storage of materials. If fencing is not possible, cover the CRZ with 6-8 inches of wood-chip mulch and 3/4-inch plywood or road boards to prevent soil compaction.

  • Route underground utilities to avoid the CRZ. If digging is unavoidable, bore under the roots or hand dig to avoid severing them.
  • Design paving away from CRZ. If this is not possible, use a porous material for driveways, such as crushed granite, pavestone, etc.
  • Save trees that are very close to buildings by using pier-and beam construction techniques that allow air and moisture to reach the root zone.


How people think tree roots grow
How they really grow

Figure 2

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