As soon as the walls of a frame building are up they should be slightly covered with common boarding, or "sheathing" as it is called in many localities. For this purpose the cheapest kind of lumber may be used ; hemlock spruce and Western white pine being most commonly used in the North, hard pine in the Gulf States, and red wood and Oregon pine on the Pacific coast. For the better class of buildings the boards should be dressed on one side to bring them to a uniform thickness, and they should be free from shakes and large knot holes.
When the braced frame is used it is customary to sheath the first story before the second story studding is set up. The sheathing or boarding should be nailed at each bearing with two ten-penny nails, although eight-penny nails are often used. If the building is built with a balloon frame, without braces, it is necessary to put the boarding on diagonally in order to secure sufficient rigidity in the frame. With the braced frame diagonal sheathing is not necessary, although it makes a better job than when laid horizontally, and all towers, cupolas, etc., should be sheathed in this way.
Roof Boarding. - In covering the roof either of wood or brick buildings two different methods are pursued : in the first the roof is tightly covered with dressed boarding, like the walls, and in the second narrow boards, sometimes called "laths," are nailed to the rafters horizontally, and with a space of 2 or 3 inches between them. The latter method is considered to make the more durable roof, as it affords ventilation to the shingles and causes them to last longer. But if the attic is to be finished such a roof is very hot in summer and cold in winter, and most architects prefer to cover the roof with boarding laid close together and then lay tarred paper over the boarding and under the shingles or slate ; this not only better protects the attic space from changes in temperature, but also prevents fine snow from sifting in under the slates or shingles. The specifications should distinctly mention whether the boards are to be laid close together or laid open, as well as the kind and quality of the boards.
Roofs that are to be tinned should be covered with matched boards, dressed one side, so as to give a smooth surface for the tin, and all knot holes should be covered with a piece of heavy galvanized iron. All rough edges should also be smoothed off with a plane. The necessity for these precautions is to prevent the tin being injured by the turned up edges of the boards when walking on the roof, or breaking through where the knot holes occur.