Floor Refinishing in San Jose

San Jose Conditions That Affect Floor Refinishing

Derived statistic, not a published normal: averaging all NOAA Local Climatological Data hourly reports at San Jose International Airport in the 4 AM and 4 PM hours (Local Standard Time) across the ten Julys 2015-2024 gives 82.1% relative humidity in the 4 AM hour (n=392) and 49.3% in the 4 PM hour (n=317), a difference of about 33 points. By the same method San Francisco International averages 61.3% in the 4 PM hour, and San Jose has the lowest 4 PM-hour average of five bay-side airport stations checked — though not the lowest in the 4 AM hour, where Hayward averages 80.9%. NOAA's Comparative Climatic Data table, a different method, gives Sacramento a 29% July afternoon mean. San Jose summers near 81°F change the finishing schedule more than the sanding. Waterborne finishes flash off faster in hot, dry air, which shortens the working window and makes lap marks easier to leave behind; we adjust application pace and airflow to the conditions in the house that day rather than to a fixed timetable.

NOAA 1991-2020 normals at the San Jose airport station give a January average high of 59.8°F and an average low of 41.8°F. January is the wettest month at 2.80 inches, and the annual precipitation normal is 13.48 inches — effectively tied with Moffett Federal Airfield's 13.45 inches. Cold, damp conditions do the reverse and stretch cure times, which mostly costs patience — a floor that is walkable is not yet a floor that is ready for furniture or rugs.

San Jose's July normal high of 80.8°F runs about 14½°F above San Francisco Downtown (66.3°F) and about 4°F above Moffett Federal Airfield to the northwest (76.9°F). August, at 81.4°F, is San Jose's warmest month. Cool, damp days in San Jose lengthen finish cure times compared with a hot, dry one — a scheduling factor rather than a quality one.

Seasonal Gaps in San Jose Floors, by the Numbers

Seasonal gaps between boards are a common reason people ask about refinishing, and San Jose's measured climate shows how much of that gapping is simply the wood moving with the seasons. Measured at San Jose Mineta International Airport, then brought to 70°F, the air averages 39.2% relative humidity over the heating season and 59% over summer, which settles wood at roughly 7.6% and 10.8% moisture content. For a traditional 2¼-inch oak strip floor that is about 0.027 inch of seasonal shrinkage per board (about 1/37 inch); for 5-inch plank, about 0.060 inch. Gaps in that range that open in winter and close by summer should not be filled — filler packed into a winter gap gets crushed out, or pushes the boards toward cupping, once the wood takes its moisture back.

Source: Hourly ASOS dewpoint observations 2015–2025, Iowa Environmental Mesonet (Iowa State University); equilibrium moisture content from USDA Wood Handbook FPL-GTR-190 Eq. 4-5; movement from FPL-GTR-282 Eq. 13-3 and Table 13-5

What's Under the Finish

The 2025 Northern California Earthquake Brace + Bolt ZIP list from the California Residential Mitigation Program lists 33 ZIP codes under San Jose, including 95002 and 95070, with the caveat 'Eligibility based on ZIP Code only, city provided as reference.' The program states that 'an EBB seismic retrofit is only done on wood-framed, pre-1980 homes with a raised foundation.' ZIP eligibility says nothing about how many San Jose homes have raised foundations. At tract level, the National Register nomination for the Fairglen Additions — 218 Eichler homes built 1959-1961 in Willow Glen — records that 'Concrete slab on-grade foundations with radiant heating were covered with 12-inch asphalt tile flooring.' That description is documented for Fairglen Additions only. Citywide, 60.4% of the 345,066 units predate 1980 but only 5.2% predate 1940, so most pre-1980 housing was built from 1950 through 1979. No source publishes a slab-versus-raised split for the city.

A slab affects what can be refinished at all. Wood over concrete is usually engineered or glued-down, and an engineered floor can only be sanded if its wear layer is thick enough to survive it — some can take a full sanding, many can take one light pass, and some cannot be sanded at all. We measure the wear layer before quoting rather than after starting.

Raised floors are where the best refinishing candidates live: solid wood over a crawlspace, often with decades of wear and plenty of thickness left. It is also where cupping comes from. Sanding a cupped floor flat before the crawlspace moisture is fixed produces a floor that goes concave the other way once it dries — so the moisture reading comes first and the sanding comes second.

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

San Jose Homes We Work In

ACS 2020-2024 five-year estimates count 345,066 housing units with a median year built of 1976: 23.3% built in the 1970s, 18.5% in the 1960s and 11.8% in the 1980s, and 52.7% built from 1950 through 1979. Only 5.2% predate 1940. Construction from 2000 onward accounts for 18.6%. 51.3% of units are detached single-family houses, and 55.8% of occupied homes are owner-occupied. San Jose's 1970s, 1960s, and 1980s stock is where refinishing pays off most: homes of that period often have original wood under carpet, and when the wear layer is intact, refinishing keeps a floor that cannot be bought new. We check thickness at a vent or a doorway before recommending it.