Engineered Hardwood in San Francisco

San Francisco Conditions That Affect Engineered Hardwood

NOAA's Comparative Climatic Data humidity table lists San Francisco (station 23272, period of record 1945-2018) at a mean July relative humidity of 91% in the morning and 71% in the afternoon, with annual means of 87% and 69%. The same table gives Sacramento a July afternoon mean of 29% and Stockton 27%. San Francisco's morning-to-afternoon spread of about 20 points is among the narrowest in the table; Sacramento's is roughly 42. Engineered hardwood exists precisely for climates like this. With San Francisco summer highs near 67°F and air conditioning drying the house out, a cross-laminated or multi-ply core moves far less across the grain than solid wood does, so seasonal gapping is much less pronounced. It is the reason we recommend engineered over wide plank widths in particular — the wider the board, the more a solid version would move.

NOAA 1991-2020 normals at San Francisco Downtown give a January average high of 57.8°F and an average low of 46.6°F. Winter lows sit well above freezing. Annual precipitation normal is 22.9 inches, of which 4.40 inches falls in January alone. Through winter the same stability works in reverse: the core resists the swelling that a solid floor would show as the house takes on moisture. Stable is not inert, though — the expansion gap at the perimeter still gets set properly.

The marine layer holds summer temperatures far below the inland valleys. The July normal high at San Francisco Downtown is 66.3°F and August is 67.9°F — roughly 14°F cooler than Redwood City, 25 miles south on the same peninsula, which normals at 81.0°F in July. Marine air moderates San Francisco's humidity swing, which suits engineered hardwood well; the same air is a reason to confirm the subfloor is dry before a glue-down rather than assuming it.

Subfloor and Foundation Work

California's Earthquake Brace + Bolt program, administered by the California Residential Mitigation Program, states that 'an EBB seismic retrofit is only done on wood-framed, pre-1980 homes with a raised foundation,' targeting cripple walls in crawl spaces beneath the structure. Twenty-eight San Francisco ZIP codes appear on the 2025 EBB Northern California eligibility list, from 94102 through 94158 — the largest block of any city in this service area. That establishes that pre-1980 raised-foundation houses exist here in numbers the state considers worth a grant program. It does not establish a share: EBB eligibility is set at the ZIP level and no source publishes a measured raised-versus-slab split for San Francisco. Alongside this, 76.5% of the city's 414,602 housing units predate 1980 and 45.2% predate 1940 per ACS. Separately, San Francisco's mandatory soft-story retrofit ordinance applies to wood-frame buildings of five or more residential units built before 1978 — that ordinance is evidence about multi-unit buildings, not about single-family foundation type, and is not used here as a proxy for one.

Over a crawlspace, engineered goes down by nail, staple, glue, or float, so the method follows the subfloor rather than the other way round. We flatten the subfloor first — engineered plank is stiff, and it bridges dips instead of following them, which is what produces hollow spots underfoot.

Source: NAHB analysis of the Census Bureau Survey of Construction, foundation type by region (2024)

San Francisco Homes We Work In

ACS 2020-2024 five-year estimates count 414,602 housing units, of which 45.2% (187,447 units) were built in 1939 or earlier. That is the single largest pre-1940 concentration in this service area by a wide margin. A further 8.4% date to 1940-1949 and 7.7% to the 1950s; construction from 2000 onward accounts for 14.4% of the stock. In San Francisco's pre-1940, 1940s, and 1960s housing, engineered often wins on height as much as on moisture: a thinner assembly clears existing door jambs, appliance toe-kicks, and the transitions to rooms that aren't being redone, which matters when only part of the house is getting new floor.