“It is indeed a different matter as regards the construction of the roof, but the water is wet all the same, and a roof is inexcusable that fails to keep all beneath it dry, however peculiar the weather may be.  No, it is not difficult to make a tight roof with the aid of common sense and common faithfulness.  The most vulnerable spots during a rain storm are beside the dormers and the chimneys, over the bay-window roofs and in the valleys, that is, wherever the plane surface and the uniform slope of the roof is broken.  In guarding these it is not safe to assume that water never runs up hill; a strong wind will drive it up the slope of a roof under slates, shingles or flashings as easily as it drives up the high tide of Lincolnshire.  It will cause the water pouring down the side of a chimney, a dormer window, or any other vertical wall, to run off in an oblique direction and into cracks that never thought of being exposed to falling rain.  ‘Valleys’ fail to carry their own rivers when they are punctured by nails carelessly driven too far within their borders; when the rust that corrupts the metal of which they are commonly composed has eaten their substance from the under side perhaps, their weakness undiscovered till the torrent breaks through; when they become choked with leaves and dust and overflow their banks; when they are torn asunder by their efforts to accommodate themselves to changes of temperature, and when ice cakes come down from the steep roofs and break holes through them.

“The other danger is peculiar to cold climates, where the roof must protect not only from driving rain but from snow and ice in all their moods and tenses.  When the higher peaks feel the warmth of the sun or the internal heat of the building, the lower slopes and valleys being without such influence, it sometimes happens that the rills will be set to running by the warmth of the upper portions, while the colder climate below will stop them in their course, building around the slate, shingles or tiles an impervious ice dam, from which the descending streams can find no outlet except by ‘setting back’ under the slates and running down inside.  Eave spouts and conductors are especially liable to this climatic influence, for nothing is more common than to find them freezing in the shade while the roofs above are basking in the sun.  As Jack observes, admitting water above an ice dam is a different kind of sin in a roof from that which caused the ruin of my plans last night, but it is no less unpardonable.  The same treatment that will make a roof non-conducting of fire will, to some extent, overcome this danger, or a double boarding may be laid upon the rafters, with an air space between.  This or the mineral wool packing will prevent the premature melting of snow from the internal heat.  The only sure salvation for gutters is to take them down and lay them away in a cool, dry place.  Thorough work, ample outlets and abundant room for an overflow on the outward side will make them reasonably safe.  In general it is better to let the water fall to the ground, as directly as possible, and let the snow slide where it will, provided there is nothing below to be injured by an avalanche.  A hundred-weight of warm snow or a five-pound icicle falling ten feet upon a slated roof or a conservatory skylight is sure to make a lasting impression.”