The inclination of the framework of the roof (which must have an even surface) should be at the rate of from 1/2 to3/4 inch per foot. The rafters or joists should not be more than 2 feet 3 inches apart, so as to give sufficient strength. As the rafters rest on the side walls, a comparatively small quantity of timber is required. Boards of 1 inch or 1-1/4 inch thick are fastened or nailed on the rafters, and should be dovetailed. These are then covered with a layer of sand 1/4 or 1/2 inch thick, in order to produce an even surface. Strong brown paper, in continuous rolls, and as broad as possible, is then laid upon it, so that each length overlaps the other by about 4 inches. When the whole or a large part has thus been covered with paper, the mixture is put into a caldron, in the proportion of tar 100 pounds to Portland cement 180 pounds. Care must be taken to heat the tar gently, and to mix the cement with it gradually, in order to prevent its boiling over. This mixture of tar and cement must then be laid on as hot as possible on the paper with a tar-brush. The next layer of paper is then laid upon it, and smoothed with a light wooden roller. In this way the whole roof must be covered. In order to break the joints of the paper, begin the second layer with half the breadth, and proceed as before. The third and fourth layers are laid in like manner, with alternate layers of cement and brown paper The last layer must be carefully covered with cement, and then strewn with sifted ashes to the thickness of 1/4 inch. Next to the gutter is a board covered with zinc, and projecting about 2 inches. It should be laid on after the second layer has been completed, so as to be covered by the third and fourth. If there are any chimneys pro. jecting through the roof, they should be surrounded with zinc immediately after the first layer has been finished.