Floor Refinishing in Mill Valley

Seasonal Gaps in Mill Valley Floors, by the Numbers

Seasonal gaps between boards are a common reason people ask about refinishing, and Mill Valley's measured climate shows how much of that gapping is simply the wood moving with the seasons. Measured at Gnoss Field, Novato, then brought to 70°F, the air averages 40.1% relative humidity over the heating season and 56% over summer, which settles wood at roughly 7.7% and 10.3% moisture content. For a traditional 2¼-inch oak strip floor that is about 0.022 inch of seasonal shrinkage per board (about 1/45 inch); for 5-inch plank, about 0.049 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's Single-Family Residential Design Guidelines direct that new buildings and additions on sloped lots be designed to relate to existing landforms — 'for example, step with the slope' — and minimize earthwork cut, fill, and offhaul. The guidelines add that any single-plane retaining or foundation wall visible from a public right-of-way 'should not exceed six feet,' and that cut banks higher than six feet should have stepped retaining walls.

Regionally, crawl space use in Pacific-division construction has declined long-term and dropped sharply only in the past decade, against 89.9% slab in new 2024 builds — so raised floors turn up more often in Mill Valley's Pre-1940, 1940s, 1950s, and 1960s stock than in anything recent. We confirm on site.

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)

Mill Valley Homes We Work In

ACS 2020-2024 5-year estimates show 28.2% of Mill Valley's 6,418 housing units (1,807, ±324) predate 1940 — a higher pre-1940 share than San Rafael (9.8%), Larkspur (9.6%) or Novato (2.5%), though Ross and Fairfax, elsewhere in Marin, run higher — with a further 11.5% built in the 1940s, 13.7% in the 1950s, and 16.6% in the 1960s. Roughly seven in ten units predate 1970, and the median year built is 1958 (±4). Mill Valley's Pre-1940, 1940s, 1950s, and 1960s 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.