Your architect shows you the elevation and there it is — the bay window that makes the room, pushing out over the rear yard. Then the planner's comment letter arrives asking how much glass is on the angled faces, how long the bay is at the yard line, and how far it sits from the neighbor's property line. None of that is a matter of taste. San Francisco writes those dimensions down.
The short answer: required yards, setbacks and usable open space in San Francisco are supposed to stay clear, and only listed obstructions may reach into them. A bay window or balcony may project 3 feet into that open area with 7½ feet of headroom, may be up to 15 feet long at the yard line, and must be at least 50 percent glass on the surfaces above the open area (§ 136).
Key numbers
| Feature | Limit | Source |
|---|---|---|
| Minimum headroom / clearance, most projections | 7½ feet | § 136 |
| Bay window or balcony, projection into a required open area | 3 feet | § 136 |
| Bay window over a street where the sidewalk is 9 feet or less | 2 feet | § 136 |
| Minimum distance from the centerline of an alley | 8 feet | § 136 |
| Glass area of a bay window | 50 percent of its vertical surfaces above the open area | § 136 |
| Maximum bay or balcony length at the open-area line | 15 feet, tapering to 9 feet | § 136 |
| Architectural projections — cornices, eaves, sills, sunshades | 4 feet | § 136 |
| Fire escapes | 4 feet 6 inches maximum | § 136 |
What a "required open area" is, and why it matters
San Francisco's planning code carves certain parts of your lot out of the buildable area: front setbacks, side yards, rear yards, and usable open space — the outdoor area a dwelling unit is required to have. Together these are the required open areas, and the default rule is blunt:
"No obstruction shall be constructed, placed, or maintained in any such required open area except as specified in this Section 136." (§ 136)
Everything below is an exception to that sentence. If a feature is not on the list, it does not belong in the yard — which is why the section is worth reading before design, not after.
The section covers four situations at once: projections over streets and alleys, obstructions in legislated setbacks and front setback areas, obstructions in side and rear yards, and obstructions in usable open space. A single bay window on a corner building can be answering to more than one of those.
Things that do not add floor area: the 4-foot allowance
The most generous allowance goes to features that are purely architectural — they do not increase the building's floor area or the volume of enclosed space. The code names cornices, eaves, sills, belt courses, sunshades, fins and brise soleils.
These may project up to 4 feet over streets and alleys, and up to 4 feet into setbacks, yards and usable open space, as long as they leave at least 7½ feet of clearance.
That is the trade the section makes throughout: the less enclosed volume a feature adds, the further it may reach.
Bay windows and balconies: the 3-foot allowance
Bay windows and balconies do add floor area or enclosed volume, so they are held to tighter numbers. Note that balconies used as the primary access to two or more dwelling units, or to two or more bedrooms in group housing, are excluded from this allowance entirely.
Headroom. At least 7½ feet.
Projection. Limited to 3 feet into the required open area. Over streets and alleys it drops to 2 feet where the sidewalk is 9 feet wide or less, and in no case may the projection come closer than 8 feet to the centerline of any alley.
Glass and openness. At least 50 percent of the sum of the vertical surfaces of the bay window — or the open portions of the balcony — above the required open area must be glass or open. Then the code says where that glass goes: at least one-third of it on one or more vertical surfaces set at 30 degrees or more to the line establishing the open area, and at least another third on the surface parallel to, or most nearly parallel to, that line. In plain terms, a bay has to read as a bay — angled glass on the sides, glass on the face — not as a solid box hung off the wall.
Length. Each bay window or balcony may be up to 15 feet long measured at the line of the required open area. From the ends of that 15-foot dimension the allowed length tapers inward along 45-degree angles, reaching a maximum of 9 feet measured along a line 3 feet out from the open-area line. Where a bay window and a balcony sit immediately next to each other and the balcony floor is at least 6 feet deep everywhere, those two figures increase to 18 feet and 12 feet.
Separation from each other. Bay windows and balconies must be at least 2 feet apart at the open-area line, with the separation widening along 135-degree angles to at least 8 feet measured 3 feet out. The adjacent bay-and-balcony pairing above is the exception.
Separation from the neighbor. Each bay window or balcony over a street, alley, setback or rear yard must also sit at least 1 foot from an interior lot line at the open-area line, widening along a 135-degree angle to at least 4 feet measured 3 feet out. That requirement is waived where the neighboring building's wall is already flush to the lot line right next to the projection.
The alternative set of limits
For obstructions within yards and usable open space, the code offers a second, differently-shaped allowance you may use instead. Under it, headroom is still 7½ feet, but the projection is limited to 3 feet or one-sixth of the required minimum dimension of the open area, whichever is less — so a narrow yard yields less than 3 feet. Each bay window may be up to 10 feet long, with a minimum 5-foot horizontal separation between bays.
That alternative also adds an aggregate cap: the combined length of all bay windows and balconies projecting into the required open area may be no more than two-thirds the buildable width of the lot along a rear building wall, two-thirds the buildable length of a street side building wall, or one-third the length of all open areas along an interior side lot line. In yards, that aggregate includes fire escapes and chimneys as well.
Fire escapes and overhead projections
Fire escapes must leave at least 7½ feet of headroom, not counting drop ladders to grade, and may project no more than necessary for safety — never more than 4 feet 6 inches into the required open area. In yards they count toward the same aggregate-length cap as bay windows, balconies and chimneys.
Other overhead horizontal projections not otherwise listed also have to leave at least 7½ feet of clearance.
Mission Bay plays by modified rules
If your project is in a Mission Bay use district, Section 136's allowances carry over but are reshaped (§ 942). In MB-R districts, obstructions over streets are not permitted at all, and projections over midblock lanes and park pathways are limited to 1½ feet.
In exchange, Mission Bay allows more design freedom in the bay itself. The Zoning Administrator may approve a bay window of any shape judged to improve the building's appearance, provided the total horizontal projection area stays within 45 square feet for each 25 feet of lot width, the projection into the required open area does not exceed 3 feet or come within 8 feet of a midblock lane centerline, and bays are separated by at least 4 feet. Corner bays get their own version: no wider than 15 feet at each open-area line, no more than 90 square feet of horizontal projection, and the same 4-foot separation. Purely decorative horizontal projections — sills, moldings, belt courses, columns, piers — may extend up to 6 inches into the clearance zone over usable open space.
Two practical cautions
A projection over public property is a license, not a right. The code states that a permit allowing a projection over a street or alley "shall not be construed to create any perpetual right but is a revocable license." You are borrowing the airspace over the sidewalk.
Vertical clearance can be higher than 7½ feet. Section 136 sets 7½ feet as the floor for projections over a street or alley, but explicitly defers to any greater clearance the San Francisco Building Code requires. Confirm both books before finalizing a height.
This article covers what the planning code allows in the required open areas. It does not cover how much you may build overall — height limits, bulk controls and rear yard depth come from your zoning district, which you can look up on the San Francisco jurisdiction page.
