What is "sarking"

Sarking \Sark"ing\, n. [From Sark shirt.] (Carp.) Thin boards for sheathing, as above the rafters, and under the shingles or slates, and for similar purposes.

n. (context chiefly Scotland Australia New Zealand architecture English) Wood, felt, or other material placed under the shingles of a roof in order to provide support or insulation; the practice of furnishing roofs with such material; an installation of such material.

Sarking is an English word with multiple meanings in roof construction:

• The use of wood panels, or "sarking boards", called sheathing, sheeting or decking in American English, under the roof covering materials such as the shingles of a roof to provide support. It is a common term in Scotland, Australia, and New Zealand. The shingles or slates are nailed directly to the sarking boards without timber battens, providing a strong, wind-resistant roof.
• An additional layer within a roof that insulates or reflects heat, such as a layer of felt, reflective foil, or polystyrene.
• Roofing felt or other type of underlayment (Am. English) under the roof covering for extra resistance to leakage.
• The word sarking is further used as part of the term scrim and sarking, a method of interior construction widely used in Australia and New Zealand in the late 19th and early 20th centuries. In this method, wooden panels were nailed over the beams and joists of the house frame, and a heavy, loosely woven cloth, called scrim, was then stapled or tacked over the top of this. This construction method allowed wallpaper to be applied directly to unplastered walls.

In current usage in Australia, sarking refers to a laminated aluminium foil layer (commonly described as RFL, or reflective foil laminate) that is installed on the roof trusses, beneath the battens, supporting a tile or metal deck roof. It acts as additional radiative and convective insulation and provides a condensation barrier.