Floor Refinishing in Sunnyvale

Sunnyvale Conditions That Affect Floor Refinishing

Derived statistic, not a published normal: averaging NOAA Local Climatological Data hourly observations at Moffett Federal Airfield, outside Sunnyvale city limits, across nine Julys 2015-2024 (July 2022 missing; Local Standard Time) gives 84.4% relative humidity at 04:00 (n=442) and 60.2% at 16:00 (n=338). NOAA's published table gives Sacramento a July afternoon mean of 29%.

The nearest NOAA station, Moffett Federal Airfield, records 1991-2020 January normals of 59.0°F average high and 42.4°F average low. Its annual precipitation normal is 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.

Moffett Federal Airfield, the nearest station, normals at a July high of 76.9°F, against 66.3°F at San Francisco Downtown and 80.8°F at San Jose (USW00023293). Cool, damp days in Sunnyvale lengthen finish cure times compared with a hot, dry one — a scheduling factor rather than a quality one.

Seasonal Gaps in Sunnyvale Floors, by the Numbers

Seasonal gaps between boards are a common reason people ask about refinishing, and Sunnyvale's measured climate shows how much of that gapping is simply the wood moving with the seasons. Measured at Moffett Federal Airfield, then brought to 70°F, the air averages 40.1% relative humidity over the heating season and 61.2% over summer, which settles wood at roughly 7.7% and 11.2% moisture content. For a traditional 2¼-inch oak strip floor that is about 0.030 inch of seasonal shrinkage per board (about 1/34 inch); for 5-inch plank, about 0.066 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 City of Sunnyvale's Eichler Design Guidelines (adopted July 28, 2009) state that Joseph Eichler built around 11,000 production homes in California, 'with over 1,000 constructed in Sunnyvale between 1949 and 1972.' The guidelines list 'Slab-on-grade construction' and 'Radiant floor heating' together among typical Eichler features, and describe the homes as having 'flat roofs, slab-on-grade construction, and open beam ceilings.' Just 1.5% of Sunnyvale's 63,239 units predate 1940 and 57.4% predate 1980, so pre-war construction is close to absent. No source publishes a citywide slab-versus-raised share.

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)

Sunnyvale Homes We Work In

ACS 2020-2024 five-year estimates count 63,239 housing units, heavily concentrated in three postwar decades: 18.0% built in the 1950s, 18.0% in the 1960s and 17.3% in the 1970s. Only 1.5% predate 1940, against San Francisco's 45.2%. Sunnyvale's 1950s, 1960s, and 1970s 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.