On a San Francisco lot with two buildings, fire separation distance is not read off the survey. California Building Code Section 202 gives three things it may be measured to; on one lot only one is available — a line between the two buildings that Section 705.3 supplies and the drawing places. San Francisco's published Planning Code Interpretations set a floor on the whole gap and say nothing about where that line goes. Section 705.9.6 states its condition on the distances from the line to each building, and carries none of the Group R-3 relief that ends the search earlier.
Key numbers
| Figure | What it governs | Section |
|---|---|---|
| 5 feet | Opening area no longer limited (Group R-3); wall rating removed (Group R-3, Type II-B or V-B) | Table 705.9 footnote f; Table 705.5 footnote i |
| 3/4 hour | Rating of the opening protectives | Section 705.9.6 |
| 15 feet | Height above the adjacent roof; distance to each building | Section 705.9.6 |
| 25 feet | Horizontal dimension of the open court | Interpretations, Code Section 140(a)(2) |
Where the line falls
California Building Code Section 705.3 makes the line exist: for wall and opening protection, projections and roof coverings, "buildings on the same lot shall be assumed to have an imaginary line between them."
Section 705.3 does not put it in the middle, and bounds the placement once. Where a new building goes up beside an existing one, the line's location relative to that building must be such that "the exterior wall and opening protection of the existing building meet the criteria as set forth in Sections 705.5 and 705.9." Nothing else places it.
What the distance is measured to
California Building Code Section 202 defines the term. Two of its three targets need a lot line or a street, and neither runs between two buildings on one lot. The third is "To an imaginary line between two buildings on the lot.", and "The distance shall be measured at right angles from the face of the wall."
Both walls measure to the same line, which the definition names but does not place.
The relief that stops the search
Section 705.9.1 ties allowable opening area to Table 705.9 "based on the fire separation distance of each individual story" — wall by wall, story by story. Footnote f is where a search can stop: opening area "shall not be limited for Group R-3 occupancies, with a fire separation distance of 5 feet or greater."
Table 705.5 footnote i sits beside it: for a Group R-3 building of Type II-B or Type V-B construction, "the exterior wall shall not be required to have a fire-resistance rating" where the fire separation distance is 5 feet or greater. Both are conditioned on Group R-3, and both govern a different obligation from the one three subsections later.
How San Francisco sizes the court
San Francisco's published Planning Code Interpretations state that, as an alternative to facing a street or alley, "a dwelling unit may face an open court which is at least 25 feet in every horizontal direction." They settle an old ambiguity: "The minimum requirement is 25 feet, not 25%, of the lot depth."
A separate interpretation, turning on an adjacent City-owned lot that "could not be considered to be part of the street right-of-way," concludes that an addition at the front of such a lot "would have to provide the open area between it and the noncomplying house at the rear." Both are floors on the gap as a whole; neither says where the line goes.
Openings above an adjacent roof
California Building Code Section 705.9.6 applies "For buildings on the same lot." It calls for "opening protectives having a fire protection rating of not less than 3/4 hour" in "every opening that is less than 15 feet" vertically above an adjacent building's roof. Then the condition:
The opening protectives are required where the fire separation distances from the imaginary line to each building or structure are less than 15 feet.
The condition is written over the pair, and the subsection prints no Group R-3 exception: the relief in footnotes f and i does not reach it.
Where the cheaper lane is, and what it costs
One lane deletes the line, and the code prices it in the same sentences. Section 705.3 Exception 1 states that two or more buildings on one lot "shall be either regulated as separate buildings or shall be considered as portions of one building if the aggregate area of such buildings is within the limits specified in Chapter 5 for a single building," and Section 705.9.6 Exception 2 exempts buildings "considered as portions of one building in accordance with Section 705.3." The price runs on: "Where the buildings contain different occupancy groups or are of different types of construction, the area shall be that allowed for the most restrictive occupancy or construction." Section 503.1.2 adds that "The provisions of this code applicable to the aggregate building shall be applicable to each building."
Which lane applies is a determination for the design professional and the jurisdiction.
What this looks like on the drawing
Three drawn things carry this: the site plan, showing the line and each wall's dimension to it; the court elevation, showing which openings sit less than 15 feet above the adjacent roof; and the window schedule, where a 3/4-hour rating appears against those openings or not.
Currency
The California Building Code sections here — 202, 503.1.2, 705.3, 705.5, 705.9, 705.9.6 — are the 2025 edition (Title 24, Part 2), updated in this library 2026-07-29. Title 24 carries no ordinance-history line, so none of them shows an amendment date, and the 2025 edition's effective date was not established here.
San Francisco's material is the 2026-08 edition of the Zoning Administrator's published Planning Code Interpretations, whose header records changes through January 20, 2026 — inside 24 months of September 2026. The "Exposure — Minimum Open Area" interpretation shows no effective date in this copy, and none was established here; "Exposure — Noncomplying Structure" is dated 9/88, older than 24 months.
Frequently asked questions
Does footnote f end the search at 5 feet?
Footnote f is scoped to opening area: it "shall not be limited for Group R-3 occupancies, with a fire separation distance of 5 feet or greater." Section 705.9.6 carries no Group R-3 relief: two different obligations.
Does a 25-foot open court settle the separation?
It sets a floor on the gap as a whole, in a different document for a different purpose, and says nothing about where the line goes. Section 705.9.6's condition is on the distances from that line "to each building or structure."
Is there an exit once the subsection attaches?
The code writes two, both exceptions rather than advice. Section 705.9.6 Exception 1 turns on a 1-hour roof assembly for a minimum distance of 10 feet from the wall facing the line, with 1-hour supporting elements. Exception 2 pairs with Section 705.3 Exception 1.
Sources
- California Building Code Section 202 — DEFINITIONS (FIRE SEPARATION DISTANCE): https://gocodebook.com/library/us/ca/ca-building-code/chapter-2-definitions/section-202-definitions#202
- California Building Code Section 705.3 — Buildings on the same lot: https://gocodebook.com/library/us/ca/ca-building-code/chapter-7-fire-and-smoke-protection-features/section-705-exterior-walls#705.3
- California Building Code Section 705.5 — Fire-resistance ratings, Table 705.5: https://gocodebook.com/library/us/ca/ca-building-code/chapter-7-fire-and-smoke-protection-features/section-705-exterior-walls#705.5
- California Building Code Section 705.9 — Openings, 705.9.1 and 705.9.6: https://gocodebook.com/library/us/ca/ca-building-code/chapter-7-fire-and-smoke-protection-features/section-705-exterior-walls#705.9
- California Building Code Section 503.1 — General, 503.1.2: https://gocodebook.com/library/us/ca/ca-building-code/chapter-5-general-building-heights-and-areas/section-503-general-building-height-and-area-limitations#503.1
- San Francisco Planning Code Interpretations, entry headed Code Section 140(a)(2) — Exposure: https://gocodebook.com/library/us/ca/san-francisco-planning-interpretations
- Related reading: How Close to the Fence Can You Build in California?: https://gocodebook.com/blog/california-fire-separation-distance-rules
Code text quoted as published in GoCodebook's library on 2026-09-13. This article does not replace permit review or professional judgment.
