=Open Wood Roofs.=--The Saxon use of timber construction survived as a tradition and was developed by the Gothic builders, in the interior roofs that sheathed the vaulting and with specially fine effect in the ceiling-roofs of churches and halls. The simplest principle of it is the so-called _tie-beam_ roof. In this, a succession of rafters slope up to each side of a ridge beam and are prevented from spreading by beams that tie them together at the foot. If the pitch of the roof were high, the construction would be strengthened by a post supported on the centre of the tie-beam, which is called a _King-post_. Instead of or in addition to this, two posts might be erected between the centre and the ends of the beams, known as _Queen-posts_. Each complete section of this arrangement is called a _truss_. It might be further stiffened by _struts_, that is to say cross pieces which, instead of tying the parts, keep them from being drawn together. The next principle is the _trussed-rafter_ or _single-framed_ roof. Since the transverse beam might interfere with the vaulting, it was replaced by one or more cross-beams near the upper angle of the roof known as _collars_. These might be further stiffened by braces, fixed diagonally from the under side of the beam to the rafter. Further, short struts or upright posts might be added near the lower angles, connecting the rafters with short, horizontal pieces, attached to the ends of the rafters and resting on the wall. These were called _sole-pieces_ and represent what would be left if the intermediate part of the tie-beam were sawn away. Sometimes an arched profile was secured by curving braces fixed to the rafters and collars. Or the collars were omitted and the curved braces were carried up to the ridge-beam, forming the variety of roof styled _arch-braced_. Frequently this style of roof was sheathed on its under side with boards decorated with ribs and bosses. The further development was the _hammer-beam_ roof, which came into general use in the fifteenth century. The hammer-beam resulted from the lengthening and thickening of the sole-piece and was supported by a curved brace, connecting its under side with a vertical piece, attached to the wall and hence called _the wallpiece_. The combination of this construction with struts, collars, and curved braces produced the magnificent effects to be seen in the roofs, for example, of =Westminster Hall= and the =Hall= of the =Middle Temple=.