Framing for Slate Roofs

FRAMING FOR SLATE ROOFS. It is the prevail ing opinion of people not familiar with the use of slate for roofing purposes, that a building should be constructed very much stronger for slate than for other roofing materials. This is a mistake, as any building strong enough for shingles, tin, or iron is strong enough for slate. Two-by-six rafters, eighteen feet long, two feet from centers, give all the strength necessary. The writer has seen hundreds of houses roofed with slate where the rafters were two-by-four, two feet from centers, sixteen feet long, with collar beam nailed across one-third of the way down from the top.

Slate can be depended upon to make a roof perfectly water-tight on any pitch down to one fifth. Half-pitch or steeper makes the best roof both for looks and strength, as it throws the weight on the walls more than on the rafters, and causes the snow to slide off clean, thereby never overloading any one part of the roof.

Matched lumber is best for sheathing for any roof; but surfaced boards from six inches to ten inches wide make a good job, and are used on a large majority of the buildings now being put up. Sheathing boards, when not matched, should be nailed at both edges on rafters, which should not be over two feet apart. Wide boards, when used for sheathing, are liable to warp and curl up at the edge, thus affecting the slate. While it may not break the slate, it raises the courses, marring the appearance of the roof. Very often a roof that lies well and smooth when done, apparently gets rough and the slates stick up. The roofer is often blamed for this when the cause is really in the sheath ing. Great care should be used in putting on the sheathing, that there are no lumps or uneven thicknesses in the boards, as they will surely show after the slate is put on. This especially applies on curved roofs or round towers, dormers, etc. In all such, the rafters should be close together and the sheathing perfectly solid and smooth. Where the sheathing is not solid

it is almost impossible to make a good smooth job, for the reason that in driving one nail it jars the next slate loose.

Fig. 119. Proper Construction at Ridge and Eaves for Slate.

Lath or strips are often used instead of sheathing boards on which to lay slate; but in such case the lath should be at least one and one-quarter by two and one-half inches, and must be spaced to suit the size of slate used. They should be placed so that the upper end of each slate will rest in the center of the lath. This plan is a good one for barn roofs, as it allows some ventilation between the slate; but where a perfectly snow-tight roof is wanted, the slate should be pointed with hair mortar on the under side of the slate at the upper end of each course, also at the joints between the slate.

Tarred or other waterproofed paper should be used under slate where the same is laid on sheathing boards. This will insure a roof per fectly tight against fine snow.

Slate roofs require about the same founda tion as shingles. The better the foundation, the better will be the roof. In beginning at the eaves, a thin cant strip is put on just above the eaves; or, in case of a roof gutter, the strip is put about a foot above the gutter, as in Fig. 119. This strip is usually about two inches wide and three-eighths of an inch thick, nailed across the roof. The first course of slate is made shorter than the other courses; or the usual size is turned and laid horizontally, so that the first two courses may be double, the same as in shingles. The lower part of the slate should project about one and a-half inches. The second course up should lap about three inches over the first or double course. When nearing the peak, the lap may be varied a little to make the slate come out right.