One of several such wooden rafters that extend from the ridge uninterrupted down to the wall plate; more massive than common rafters, and framed into a tie beam that makes the whole assembly more stable.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
In a timber-framed house, one of several such rafters that extend from the ridge of the roof down to the wall plate; somewhat heavier than a common rafter; often located at a corner post, story post, or chimney post and framed into a tie beam. Principal rafters, together with the principal purlins, form a roof framing system having considerable stability. Also called a blade.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.