Concrete slab
In-situ relative humidity probe (ASTM F2170)
Target: ≤ 75% RH for most adhesives; ≤ 85% RH for some LVP systems
Probes sit in the slab for 24 hours before reading. A surface meter is a screening tool, not a result.
Pro edition
Subfloor & Moisture Report
Almost every failed floor failed underneath, and almost every denied warranty claim was denied because nobody wrote down a number before the material went in. This is the sheet we fill out on your job — and the one you can hold any installer to.
What gets measured
Concrete slab
Calcium chloride (ASTM F1869)
Target: ≤ 3 lbs / 1000 sq ft / 24 hr
Older method, still specified by some manufacturers. Measures surface emission only.
Wood subfloor
Pin or pinless moisture meter
Target: 6–9% in most of the US; within 2% of the flooring itself for solid, 4% for engineered
The gap between subfloor and flooring matters more than either number alone.
Ambient
Thermo-hygrometer
Target: 60–80°F, 30–50% RH, held for the acclimation period and after
A house that swings outside this range seasonally will move the floor no matter what was installed.
Tolerances, by material
| Specification | Value |
|---|---|
| Flatness, most nail-down hardwood | 3/16" over 10 ft |
| Flatness, most floating LVP | 3/16" over 10 ft |
| Flatness, large-format tile (≥15") | 1/8" over 10 ft |
| Solid hardwood acclimation | 3–5 days on site, in the room, out of the box |
| Engineered hardwood acclimation | 48–72 hours; some products none at all |
| Expansion gap at walls | 3/4" typical, covered by base and shoe |
Pre-install checklist
Ten items. If an installer cannot answer all ten before material is ordered, the quote is a guess.
- Slab or wood subfloor identified, and its age
- Moisture readings taken, recorded, and dated
- Ambient temperature and RH logged at the same time
- Flatness measured with a 10 ft straightedge, deflection noted room by room
- Existing floor layers identified — including anything floated over
- Pre-1985 sheet vinyl flagged for asbestos screening before demo
- Vapour barrier requirement confirmed against the manufacturer spec
- Acclimation start date agreed and material delivered
- Expansion gaps planned at every wall, column and threshold
- Transitions and thresholds specified where material or height changes