This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
147. Snow guards made in various forms are used on all kinds of roofs to prevent the snow from sliding down into the gutters, thus clogging them, and causing the water to overflow outside of the building. Where snow accumulates and freezes in a gutter, it is likely to form a dam and back the water up under the slate, tile, or shingles, as the case may be, and eventually finds its way into the interior of the house. Snow guards also prevent the dislodgment of large quantities of snow, which might cause injury to persons in the vicinity, as well as to ornamental shrubbery. For these reasons they should be applied to roofs having a steep pitch towards the street.
148. The guard generally used is made in four different styles, and is constructed with galvanized-iron or copper wire.
At (a), Fig. 133, is shown a fa).
guard used with convex tiles; the loop a acts as the snow stop and stands above the tile about 2 inches; the shank b is of sufficient length to extend well back on the tile, and is made flat so that it presents the least thickness at the tile lap; the end is turned down and out and is kept flat at c, to give a driving surface over the nail point d, and to raise the guard to the height of the tile.
At (d), Fig. 133, is shown a guard made for flat or concave tiles; the loop and shank are the same as at (a). The nail point is turned down without forming a knee, because the tiles do not stand more than 3/8 inch above the roof.
At (a), Fig. 134, is shown a guard used for metal roofs, with lock seams. It is secured to the roof under the lock by a galvanized-iron nail driven through the loop at the back.
At (b) is shown a guard used for slate or shingle roofs. This guard is set between the edge joints of the slates or shingles, and the nail point is driven into the roof boards. Should this form of guard be bent down by the weight of snow and ice, it may be readily pressed hack, without breaking, into its proper position. Guards are also manufactured of cast iron, but, being clumsy, they are not to be recommended.
Guard rails are also clumsy and unsightly; they gather the snow in a drift, which dams up the water, with the result before mentioned; on the other hand, the wire snow guards placed all over the roof are almost invisible, and hold the snow until it melts and disappears.