Furring

In construction, furring (furring strips) are strips of wood or other material applied to a structure to level or raise the surface, to prevent dampness, to make space for insulation, to level and resurface ceilings or walls,[1] or to increase the beam of a wooden ship.

They can be laid out perpendicular to studs or joists and nailed to them, or set vertically against an existing wall surface.

[2] Metal furring strips are used for commercial projects, or in towns where fire-proof supporting elements are required by the local building code.

Often called "hat channels" to describe the profile (cross section), they consist of two flanges on each side of a trapezoid shape, 7/8 in thick.

Drywall has become the most common interior wall finishing material and does not need furring due to its strength.

Vertical, metal furring is applied to the wall to create a channel and receive the siding material
A Furring "is performed by ripping off the planks, and putting second timbers upon the first timbers, and upon them again other planks. And all this is done to make a ship to bear a better sail" (Perrin 1929, 92).