Duck roofing has been successfully applied by first laying and tacking down a covering of two-ply asphalt paper, and upon this was spread a covering of resin-sized sheathing paper, tacked in the usual manner. Upon this was laid a covering consisting of cotton duck, forty-four inches wide and weighing twenty-six ounces to the yard. Several methods of joining the edges of the duck together have been tried, resulting in the abandonment of the method of sewing used, for the preferable method of nailing the duck down, laying one strip over the other, and then opening the duck, a lock joint is formed without any jointure between the two sheets exposed to the weather. After the duck is stretched on the roof, it is securely fastened by means of round-headed woodscrews, one and one-fourth inches long, through a concave tin washer three-fourths of an inch in diameter, resting upon a seven-eighths of an inch washer made of roofing felt.
A coat of hot pine tar with a small quantity of linseed oil is laid upon the whole of the duck roofing, after being laid, for the purpose of filling the fiber and preserving the cotton fabric by means of the antiseptic principles of the pine tar. The surface is then covered with two coats of mineral paint.
Within a year, paper has been very successfully used as a roof covering. Sheets of wood pulp board about one-sixteenth of an inch in thickness are treated by a process which renders them hard and elastic, and secured upon the roof by means of tacks through concave tin washers. The edge of each sheet is grooved, in order to allow for the expansion and contraction of the roof. The whole roof is then covered with a heavy mineral paint. Experience with this during the past severe winter in Maine has been of the most satisfactory nature.
Shingles furnish a much better roof covering than slate, both in the matter of conduction of heat or cold in the extremes of summer and winter and also in resistance to fire. The heat of a slight fire underneath the roof will cause slates to crumble; and the same result will be obtained by heavy sparks falling and burning upon the roof. Some people treat shingles by boiling them under pressure in a solution of salt and chloride of lime, for the purpose of antiseptic treatment and also to render them fireproof.
STOREHOUSES.
The latest form of storehouses tends to one of two extremes. Where land is nearly level, and cheap, the greatest storage capacity can be obtained with the greatest economy by means of a one or two story storehouse built with a plank construction, with the beams secured to the posts by means of knees. A traveling crane or railroad runs along the middle of the storehouse, affording a ready means for rapid changes of the contents of the storehouse.
Another form for storage is by means of very large brick buildings, especially arranged as a protection against outside fire. In designing a storehouse it is of especial importance that the stories should not be made so high that it will be possible for a dangerous load to be piled upon any one floor.
The wool storehouse of the Pacific Mills at Lawrence can be safely said to be in its design and construction the finest example of mill engineering in the country.
Another type of mill storehouse, designed for both raw material and finished goods, is designed by Mr. John Kilburn, of Lowell, and consists of two buildings
placed at right angles to each other, and joining only at one corner. These buildings do not contain openings through the floors of any nature whatsoever, either for stairways, elevators, or any other purpose; but all vertical communication is furnished by means of a masonry tower at one corner of the buildings, which contains an elevator and stairway. At the level of each floor, substantial balconies lead through a doorway in the tower to one in the storehouse, and the storage is added to or withdrawn from the storehouse in this manner.