Principals

Principals
in a roof of double-framed construction, the main as opposed to the common rafters.
Pulvinated Frieze ...

Bay: Internal division of building marked by roof principals or vaulting piers; A unit of interior space in a building, marked off by architectural divisions.

Principals - the main inclined timbers in a roof.
Purlin - a continuous horizontal timber running parallel to the ridge, sometimes referred to as side timbers.
Queen post - a pair of vertical timbers rising from a tie beam to support purlins.

As a rule in such cases the rafters are divided into stronger principals and weaker subsidiary rafters.
Hipped: roof with sloped instead of vertical ends.
Mansard: roof with a double slope, the lower slope being larger and steeper than the upper.

Innovative architectural ideas began from the Classical principals that had dominated the Renaissance, further stimulated by the often clever and surprising buildings of the mid and late 16th century.

Scissor braces: paired braces crossing diagonally between pairs of rafters or principals. Wind-braces: short, usually curved braces connecting side purlins or ridge piece with principals.

America's first leaders modeled their homes after the grand manors of Europe, borrowing classical principals from ancient Greece and Rome.

See also: Principal, Timber, Architecture, Church, Classical