fur

To fur is to attach thin strips of material, called furring strips, to an existing surface in order to create a new plane that is level, plumb, or properly spaced. Furring transforms an uneven or unsuitable substrate into one that will accept finish materials like drywall, flooring, or cladding. The verb describes the process itself; the noun fur can refer either to the strips being applied or the completed assembly.

Furring strips are typically wood (1 by 2 inch or 1 by 3 inch lumber) or metal channels, fastened horizontally or vertically to concrete, masonry, existing studs, or other structural elements. A builder furs out a basement wall to bridge over bumps and create a cavity for insulation and services. A floor is furred when joists sit unevenly, using shims or new strips laid across the top to achieve a level surface for subfloor installation. Metal furring is common in commercial work and offers better dimensional stability than wood.

The spacing and orientation of furring strips depend on the finish material. Drywall typically requires furring every 16 or 24 inches on center. Tile or stone cladding may require closer spacing and thicker strips to support weight and allow for substrate movement. Before fastening, the substrate must be assessed for rot, loose material, and structural integrity. Fasteners are chosen to suit both the strip material and the base: masonry anchors for concrete, driven nails or powder-actuated fasteners for existing wood, and self-drilling screws for metal-to-metal connections.

Variants and complications

Furring a basement wall to create a sealed cavity requires coordination with drainage and vapor barriers. Moisture trapped between the fur and the wall can cause rot and mold. Furring around mechanical penetrations, electrical boxes, and window frames demands careful framing to maintain code-compliant air sealing and insulation integrity. Over-furring a floor or wall can reduce usable space and increase material cost; under-furring leaves lippage (uneven surface variation) that becomes visible after finish.

The term likely derives from the Old French fourrer, meaning to line or pad, which captures the literal action: covering a rough surface with a protective, leveling layer. In contemporary construction, furring is routine in renovation and retrofit work, where it solves the problem of imperfect existing conditions more cheaply and faster than removing and rebuilding the substrate.