The apertures required in walls are chiefly those for doors and windows.

Heads

Each opening is generally closed at the top, either by an arch, as shown in Figs. 94, 98, 525, 549, etc., or by a "lintel" of stone, as in Figs. 143, 542, 543, 547.

In many cases the head is of an ornamental character, weak in itself, and requires to be protected from undue pressure by a relieving arch, as described.'at page 52.

Jambs

These are the sides of the openings, and may either be square, or formed with recesses to receive the frame for the door or window.

1 Sc. for "gatherings" - Incomes or Oncomes.

Revealsl are the portions of the sides of the openings left in front of the recesses for the frames (a b in Fig. 18). They are probably so called because they are revealed, or exposed to view, whereas the rest of the sides of the opening is generally hidden - the recesses by the frame which fits into them; and the remainder by linings. The jambs behind the reveals may either be square, as in Fig. 17, or splayed, as in Fig. 18. Openings with splayed jambs weaken the wall more than when the jambs are square. They are, however, convenient in order to afford room for shutters, etc. The thickness of the reveal is generally from 4 1/2 to 9 inches in brickwork, or from 6 to 12 inches in stone, but varies accord-iiior to circumstances.

Sills.2 - The lower side of the opening is generally finished, both in brick and stone walls, with a sill of stone in one piece, and about 5 or 6 inches longer than the opening. This forms the base of the window, and supports the oak sill of the sash frame.

Window Sills should be set so as to bear only on the ends, the intermediate portion being left quite clear, with a hollow space underneath, as the weight of the piers of the window will probably cause a greater settlement in the wall under the ends of the sill than under the centre, in which case the sill would be pressed upwards in the middle, and broken. The space is subsequently pointed up.

Sills should project at least 2 inches over the face of the work and be throated so that they may keep the wet off the wall below them.

Different ways of finishing the ends of sills are shown in Figs. 541, 542, 544, 545, 547.

Door Sills are also of stone, in a single piece, except for internal doorways, where they may be of oak.

Fig. 16. Square Jambs, no Reveal.

Fig. 16. Square Jambs, no Reveal.

Fig. 17. Reveal with Square Jambs.

Fig. 17. Reveal with Square Jambs.

Fig. 18. Reveal with Splayed Jambs.

Fig. 18. Reveal with Splayed Jambs.

1 The term reveal is somewhat loosely used, and is often applied to the width a c required for the frame. 2 Sc. Sole.

Holes are sunk in these sills to receive the studs at the foot of the door frame.

The sill of an external doorway is generally formed by a stone step (see Fig. 524).