With slating or tiling greater care is necessary than with shingles. Neither slates nor tiles will lay as closely to the roof, or to each other, as shingles, and for this reason, the boarding should always be matched, and tarred paper always used, as circulation of air is no object with slates. The lap of slates should vary with their length, always allowing at least three inches head-cover, that is, each slate must lap three inches below the head of the second slate below it. Tiles are constructed with a variety of joints and laps, each designed for the needs of the different forms of the tiles. Both slates and tiles should be put on with galvanized nails, which must not be driven too hard for fear of cracking and yet hard enough to prevent loosening or rattling, and if the cost is not too great, copper should be used for all gutters and flashings. It is a good practice to lay the first three or four courses of a slate roof above the gutter in elastic cement, and also all hips and ridges.

Window Frames

Following the completion of the roof will come the preparation of the side walls to receive their finish, and the first thing to be done is to set the window frames. In wooden houses the stud will usually make one side of the weight box, and the frame will consist only of the "pulley stile" and casing. Sometimes the boarding is kept back from the edge of the studding and the casing is set upon the studding with a piece of finish or a "back-band", put over the joint with tarred paper, or better still, strips of zinc, to keep out the water. (Fig. 38.) In case the frame is set against the usual four-inch studding the outer casing will form one side of the groove in which the sash slides, but in the other case there will be room to put a strip five-eighths or three-quarters of an inch wide inside of the casing, moving the sashes in and leaving a space for mosquito guards. (Fig. 39.) The top of the frame must be flashed with lead and the bottom of the sill grooved, to receive the top of the shingles or clap-boarding, which will be begun as soon as the frames are set. Pockets of canvas, in which the window sill is set, are advisable in exposed situations.