double-course

Double-course describes a construction technique where materials are laid in two parallel rows or layers rather than one.

In roofing, double-course shingles overlap more than standard installation, creating deeper shadow lines and better weather protection.

In masonry, a double-course of bricks provides extra thickness at foundations or decorative bands.

On stringed instruments like mandolins and twelve-string guitars, double-course means pairs of strings tuned in unison or octaves, played together as a single unit.