For a similar reason, it is necessary to form a ledge, either by reducing the size of the pier above, or by corbeling out, at the window openings, as shown at _g_, for the support of the floor planks at _h h_. On the top of the corbel so formed, usually a 3" × 8" yellow-pine piece is securely anchored to the wall, to provide a bearing for the ends of the rough floor planking. =26.= Reference to _i_ and _j_, Fig. 7, shows that there is very little room between the head of the window and the bottom of the floor construction. By this means, the maximum amount of light near the ceiling is obtained, and, besides, the ventilation is greatly facilitated. This is one of the important features in factory designing, as well as in school-house architecture. =27. Foundation Walls and Piers.=—From the section of the wall shown at _k k_, Fig. 7, it will be observed that the entire building is practically supported on heavy piers, and that the 13-inch walls below the window sills are only spandrel fillings. In some instances, 9-inch walls can be used in these places, but it is not considered advisable from the fact that beating rain will readily drive through a 9-inch wall, and, besides, there is hardly sufficient sill for a heavy window frame. Attention is particularly called to the construction of the window sill at _l_. In the better class of construction, heavy bluestone sills 5½ in. × 7½ in. would be used; but for cheap work, it is customary to use a light 3" × 5" bluestone sill. Where spandrel fillings more than 13 inches in thickness are used, or where the thickness of the wall is much greater than the frame, as indicated at _m_ in the basement, beveled bricks on edge are used for forming the sloping wall inside. The purpose of the sloping sill is to prevent the corners from being broken and damaged, and employes from occupying them. =28. Terra-Cotta Window Heads.=—In factory construction, the use of terra-cotta window heads is not unusual, and the construction of such a window head is indicated at _n_, Fig. 7. Where terra-cotta window heads are used in this manner, some means of support must be had for the brickwork above the window head, as terra cotta in itself is of little use as an arch, or lintel. It is not uncommon to use angle irons back to back, as indicated on the section of window head _n_. This construction, of course, can only be used where the wall runs parallel with the supporting floor, for if the head of the window receives beams or girders it must necessarily be more strongly and rigidly constructed with heavy channel irons, or =I= beams.