Flooring · definition
A thin layer between subfloor and finish floor for smoothing, sound, moisture, or cushioning. The required type depends on the finished floor.
Source: APA — Plywood Underlayment (Builder Tip R340)
Where this term lands on a Columbus budget
The cost pages carry the current local ranges, and the guides explain what moves them. A published range becomes a project number only after someone looks at the site.