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Crown and shrub spacing
Tree and shrub spacing is defensible-space guidance, not Oregon R327. CAL FIRE and the Board of Forestry key horizontal gaps to slope. IBHS Base, in the 5–30 foot band, wants two times the tallest plant, capped at 10 feet, and no shrubs under larger trees. Zone 0 is a different, tighter band. See Zone 0.
You are in the yard with a tape. Two canopies almost touch. A 3-foot shrub sits under a pine. That is the measurement this page is about.
FA Exhibit ZON-011 draws the BOF slope-keyed table at the gentle-slope case. Distances are guidance, not a permit. Illustrative, not a construction document. CC BY 4.0.
Why it matters
Crowns that touch carry fire. Shrubs under trees are a ladder. That is a defensible space job. It does not replace vents, roofs, or walls. Oregon’s construction code does not print this table.
How the numbers split
| Document | Horizontal | Vertical |
|---|---|---|
| CAL FIRE dspace | Shrub spacing as a multiple of height by slope | At least 3× shrub height to the lowest branches. Example: 5-foot shrub → 15 feet |
| IBHS Base 5–30 ft | 2× tallest plant, max 10 feet. Groups under 10-foot foliage count as one shrub. No hedges | Do not place shrubs under larger trees |
| Prescott Appendix B, 5–30 ft | 2× tallest plant, max 10 feet. Clusters max 10 feet wide; no continuous or privacy rows | Remove plants and shrubs under larger trees; crowns within 10 feet of structures need 10 feet of clearance |
| Oregon R327 | Not a planting table | Not a planting table |
Measure canopy edge on the CAL FIRE / BOF tree rule this exhibit draws. Do not silently switch to trunk-to-trunk.
The paths
1. California lot with defensible-space rules. Follow CAL FIRE’s page and the BOF table the exhibit draws. Zone 0 remains empty of plants.
2. IBHS designation. Read 2.2.2. The 10-foot cap is IBHS, not a rewrite of a steeper-slope BOF row.
3. Oregon construction. R327 still does not space your trees. OSFM and Firewise guidance can still apply as guidance. See zone bands.
4. Prescott permitted work. Appendix B is part of Prescott’s current local WUI code and requires a vegetation-management plan for projects permitted under that code. Its 5–30 foot spacing resembles IBHS numerically, but it remains a separate local instrument with its own 30–100 foot cap.
5. Ladders. Vertical clearance is ladder fuels.
What people mix up
- Writing a BOF table onto an R327 drawing.
- Measuring trunk to trunk when the document said canopy edge.
- Planting the 5-foot band because the shrub is “fire-resistant.”
- Treating IBHS’s 10-foot cap as CAL FIRE’s 3× vertical rule.
How to check
- Name the document you are scoring.
- Measure canopy edge or shrub height the way that document says.
- Look under the trees. If a shrub is there, you have a ladder issue too.
- Walk Zone 0 separately.
Limits
This page does not spec a species. ZON-011 is illustrative. FireApproved is not the AHJ and not a forestry inspector. Do not scrape a private planting plan.
Related records
Questions
Is crown spacing in Oregon R327?
No. R327 is a construction section where adopted. Spacing trees and shrubs is defensible-space guidance or a designation standard. Do not write a BOF table onto an Oregon structural drawing as code.
Do I measure trunk to trunk?
CAL FIRE and BOF guidance for this exhibit measure canopy edge to edge for trees, and a multiple of shrub height for shrubs. IBHS Base uses two times the height of the tallest plant, maximum 10 feet, between individual shrubs or small groups. Do not mix trunk-to-trunk with canopy-edge without naming the document.
What if my lot is narrower than the table?
Do the work you can on your lot. Neighboring fuels are a different legal problem. This page does not invent a 50-foot-lot exception.
Does Prescott use the same shrub-spacing numbers as IBHS?
Prescott's current Appendix B uses twice the tallest plant, capped at 10 feet, in its 5–30 foot Intermediate Zone and removes shrubs under larger trees. The numeric resemblance does not make IBHS the city's code. Prescott also limits clustered shrub width and continuous rows, and its 30–100 foot Expanded Zone caps required spacing at 6 feet.