A type of timber construction in which curving paired members (blades) rise from ground level to a tie-beam or collar-beam which supports the roof timbers.
Basement
Lowest, subordinate storey; hence the lowest part of a classical elevation, below the piano nobile or principal storey.
Basilica
A Roman public hall; hence an aisled building, especially a church, with a clerestory, i.e. windows in the walls rising over the aisles.
Basket arch
A three-centred and depressed arch, or one with a flat centre; also called anse de panier (French, lit. basket handle).
Bastion
One of a series of defensive semicircular or polygonal projections from the main wall of a fortress or city.
Batter
Intentional inward inclination of a wall face.
Battlement
Defensive parapet, composed of merlons (solid) and crenels or crenelles (embrasures or openings) through which archers could shoot; sometimes called crenellation. Also used decoratively. Irish battlements have the up-and-down rhythm of merlons and crenels interrupted at the corners, which are built up in a series of high steps; typical of late medieval Irish architecture.
Bawn
(Irish, lit. ox fold): Defensive walled enclosure attached to, or near, a tower house or Plantation castle.
Bay
Division of an elevation or interior space as defined by regular vertical features such as arches, columns, windows etc.