Floor Flatness in Oregon: The Number Before You Buy
Flatness is the one specification that applies to every material on this site, it is measurable with a straightedge, and it is the most common reason a quote goes up after the job starts.
The tolerances
- Plank — wood, laminate, vinyl: about 3/16 in over 10 ft.
- Ceramic and porcelain tile: about 1/8 in over 10 ft, and tighter for large-format tile where lippage between adjacent pieces is what people notice.
- Natural stone: the same flatness as tile, plus a stiffer floor under it.
These are manufacturer specifications and the warranty is written around them. A floor laid over a substrate that fails the tolerance is not a covered floor, whatever else goes wrong later.
How to measure it yourself
Borrow or buy a ten-foot straightedge. Lay it on the floor in several places and in several directions, and measure the largest gap underneath with a tape or a coin. Do the doorways and the middle of the largest room; those are where deviation shows up. Ten minutes, no tools you cannot buy at a hardware store, and it tells you before anyone quotes whether leveling is part of this job.
Flat is not the same as level
A floor can slope noticeably across a room and still be perfectly flat, and flat is what the tolerance is about. Plenty of prewar Portland and Salem houses sit visibly out of level and take a new floor without complaint. Conversely a floor that reads level with a spirit level can have a dip in the middle that fails the specification outright. Measure the gap under a straightedge, not the bubble.
Deflection is the number underneath the number
Flatness is about the surface. Deflection is about how much the floor structure bends when someone walks on it, and tile and stone care about it far more than plank does. The usual specification is L/360 for ceramic and L/720 for natural stone — the span divided by that figure is the maximum permitted deflection. In an older west-side Oregon house with 2×8 joists on wide centers, meeting L/720 often means sistering joists or adding a subfloor layer, and that is a carpentry line rather than a flooring one.
What fixing it costs and who should do it
Small dips are filled with a patching compound. A whole room that fails is a self-leveling underlayment, poured, and it is priced by area and by depth. Either way it belongs in the quote as its own line before the job starts. A leveling line that appears on the second morning is the most common cost surprise in this trade, and the reason is almost always that nobody put a straightedge down first.
The one case where flatness is not the constraint
Carpet. It is laid over a pad and stretched onto tack strip, and it will happily cover deviations that would fail every plank manufacturer’s tolerance. In an older house that sits visibly out of level, that is a real advantage. What carpet will also cover is a springy or soft spot, and that is a structural question rather than a flooring one — walk the whole floor before it goes down, not after.