This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
Cornices. For these, terra cotta is greatly used, as it is much lighter, and usually cheaper, than stone, especially if the work requires elaborate decoration. When a stone cornice is built, it is always necessary, in order to balance it, that the projection of the pieces composing the cornice shall be less than the portion extending into the wall. A terra-cotta cornice, however, does not require this, as the various pieces may be made to enter the wall only from 8 to 12 inches, being held in place by ironwork embedded in the masonry. Small angles, I, or T beams are generally used to support the projecting pieces of a cornice. If the projection is considerable, the inner end of the beams should be anchored by rods carried down into the wall until there is enough masonry above the anchor to insure stability. When the wall carrying the cornice is light, it is well to anchor the top of the wall to the roof timbers, so as to prevent its inclining outwards. If iron is to be used for tying the cornice to the wall, it is necessary to determine the method of anchoring before the pieces are molded, as, in manufacturing them, holes or slots must be made for inserting the beams, rods, and anchors.
149. The method of placing and anchoring terra-cotta cornices is shown in Figs. 73, 74, and 75. In Fig. 73 is represented a cornice having a projection of over 3 feet. At a is shown the bracket extending into the wall, and held in place by an iron rod b bolted to the angle c, which runs longitudinally through the wall; the rod b has an anchor plate at its lower end.
In Fig. 74 is shown another cornice, having considerable projection; a shows the bracket; b, the crown mold; c, a tie or clamp holding the upper portions of the cornice together; d and e, anchor rods tying the various portions of the cornice to the wall; f and g are respectively the angle and anchor rod. In Fig. 75 is shown a more elaborate cornice, having a projection of 4 feet. It is essentially similar to those just described, the principal difference being in the use of angles extending into each bracket, supporting it as shown.
150. Terra cotta is also very extensively used for roofing purposes, but as that subject is dealt with in Roofing, it is unnecessary to consider it in this place.