What is probably hiding

The rule

Assume the expensive problems are the invisible ones, because the visible ones were already priced.

The list I actually work through

Foundation type, starting with brick. San Francisco has a great deal of housing stock old enough to sit on unreinforced brick or rubble foundations. This is not automatically disqualifying and it is not automatically cheap. It changes the cost of nearly every subsequent improvement, because you cannot add mass above a foundation that cannot carry it. With the right engineer, you can identify the material before you begin imagining an addition.

Skylights, roof decks, and every place water is asked to change direction. Skylights leak. Roof decks over occupied space leak. Both are frequently repaired cosmetically from below, which conceals the symptom and preserves the cause. Look for patched drywall at a skylight well and fresh coating on a deck membrane, and ask directly whether either has ever leaked. In the homes I have built, roof decks and terraces required their own waterproofing review, negative-pressure testing at openings, and floor drains in wet areas — because water in a horizontal assembly does not announce itself until the substrate is gone. It is worth the time to have a waterproofing and roof inspection.

Improvements without permits. A property's permit file is its autobiography, and the interesting chapters are usually the missing ones. Pull the record and compare it against the floor plan in front of you. A finished lower level, a rear deck, a converted garage with no corresponding permit is not merely a compliance question — it is a valuation question, because unpermitted space is inconsistently counted and may need to be removed or legalized. Legalization is not instant: the City's own March 2026 audit found a 280-day median from filing to issuance for in-house permits adding housing in the older cohort, against a 114-day median for applications filed on or after January 1, 2024 (SF Board of Supervisors Budget & Legislative Analyst). Faster than it was. Not fast.

Structures on land you do not own. This one is missed constantly. Stairs, retaining walls, planters, garden walls, ramps, and bay projections routinely sit in the public right-of-way. In San Francisco those may sit without easements — and without an easement, the right to keep them there may not be yours. Minor sidewalk encroachments are permitted under Public Works Code §723.2 at the Director's discretion and are revocable at will, and are subject to an annual public right-of-way occupancy assessment fee whether permitted or not (SF Public Works). Major encroachments require a resolution of the Board of Supervisors, carry insurance and indemnity obligations, and are expressly non-exclusive and revocable (SF Public Works, Public Works Code §786). Planning Code §136 says it plainly: a permit for a projection over a street “shall not be construed to create any perpetual right but is a revocable license” (SF Planning Code §136). Confirm what is permitted, confirm it is recorded, and price the restoration obligation if it is not.

Retaining walls. On San Francisco's grades, many properties are held up by a wall built by a neighbor, or by nobody documented. Determine who owns it, whether it was engineered, whether it drains, and whether it is leaning. A failing retaining wall is a six-figure problem in a place where equipment cannot reach.

And two things nobody has protected for you. Views from private property are not protected under San Francisco City regulations; the General Plan protects specified public view corridors, not your window (SF Planning Urban Design Guidelines). Planning Code §295 is a park-shadow control, not a private view right, and it exempts structures at or below 40 feet (SF Planning Code §295). If the view is why you are buying, verify the height limit on the parcel across the street, not the view from the living room.

Separately, on seismic: the mandatory soft-story program under SFEBC Chapter 4D reaches unstrengthened wood-frame buildings of three or more stories with five or more residential units, permitted before January 1, 1978 — it is not a blanket single-family mandate, and DBI identifies a voluntary AB-094 path for Type V wood-frame homes (SF DBI Information Sheet G-23). Owners of noticed concrete buildings face a screening deadline of June 9, 2027 (City of San Francisco). Not applicable to most houses; essential if it applies to yours.

Who to bring

Two specialists earn their fee on nearly every significant San Francisco purchase: a geotechnical engineer, because this is a city of sand, fill, bay mud, and rock within a few blocks of one another; and a structural engineer, because the question is never whether the house is standing but whether it is standing the way someone intended. On the properties I developed, geotechnical and structural review were not contingency-period luxuries. They were the first two calls.

I once had a client who went further and retained an acoustical engineer to measure evening conditions at the site — city noise — and another that measured electromagnetic fields. I would not put that on a standard checklist. But they bought a quiet house, and they have never once wondered about it.

What this means for you

If you are buying: Order the geotechnical and structural reviews early enough that the findings can still affect price. Pull the full permit history yourself and read it against the plan. Ask about every horizontal surface over occupied space. Assume nothing about the view.

If you are selling: Every item above will be found. Being the person who produces the retaining wall engineering, the closed permits, and the roof deck warranty is worth real money, because it converts an open-ended risk into a documented condition.

If you are a fiduciary: Commission the engineering rather than relying on a general home inspection. A general inspection is a screening tool. It is not a defensible basis for a fiduciary's valuation or disclosure position.