Solar in San Francisco has to be honest about fog. Western neighborhoods can stay gray through the hours when a valley roof is already in full sun. Eastern slopes may get a clearer morning and then lose the day. Tall neighbors, parapets, and the next house up the hill shade flat roofs that look wide and empty in a photo. Roof decks, vents, and stair penthouses compete for the same surface. Production will not match a brochure shot in a bright inland county. If the layout ignores fog and shade, it is describing a different city.
The roof underneath is usually flat and often tired. A membrane that ponds or a parapet that leaks should be corrected before anyone anchors an array through it. There may be no attic, so the ceiling of a bedroom is directly under the work. Walking a soft deck is how a leak starts in the plaster below. Pitched sections over bay windows are small and fussy. A south-facing plane sounds ideal until a neighbor's wall covers it after midday. Ask for a layout that shows shade by time of day, not a rectangle dropped on the biggest open patch.
Gear has to live in wind and damp. Attachments, conduit, and shutoffs corrode. The path to an older electrical panel may run through a finished stair and a tight closet. Some buildings have rules about what is visible from the street, so the conversation should include where the equipment sits, not only how it faces. Production will dip in long gray stretches and rise on the clear days the city does get. Ask how the array comes off when the membrane needs work. That question matters more here than a sunny-state assumption.
Call with the roof shape, the shade from neighbors, and how foggy the block actually is. Mention soft spots, a roof deck, or a panel that is already full. The useful talk is whether this San Francisco roof, in this fog, has a workable layout.
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