Plates on the outer walls are 3 × 10, and on inner walls 3 × 8 inches. The main studding is lined on both sides with moisture-proof sheathing, and boarded up with matched lumber. The inclosed space is filled with non-conducting substance, usually sawdust or spent tan bark. The filling must be dry and packed tightly. The inner 2 × 6 studding is lined with sheathing, and then boarded up with matched lumber. The joints of this studding should be made with care and the lumber selected, no crooked stock being used. Sealing up these joints with pitch adds to their efficiency, and also to the durability of the lumber. The outer studding is covered with weather boarding or ship siding. Twelve inches at the bottom are left open and hinged covers swung over them, which can be opened or closed as ventilation requires. [Illustration: FIG. 49. PLATE _B_. CROSS SECTION.] The interior walls have 4 × 8 inch × 40 feet posts, and 3 × 8 studding, which are boarded on either side with matched lumber and filled. The lower section of these walls, to a height of ten to fifteen feet, is often left without filling, as it is more exposed to the ill effects of moisture, and requires renewal before the upper portion. This is more conveniently done where no filling is in the wall. In the center of each room, on the end at which the ice cakes enter, an opening is left extending from the sills to the plate. As the house is filled with ice these openings are closed up. Boards are provided, when building, which will fit into place and make the walls at these openings, as near as practicable, the same as in other places. The middle section being filled and planked by the inner and outer air spaces. At the opposite end of the rooms a similar opening is provided. For closing it a slightly different plan is adopted. The outer section is divided into doors five or six feet high, swung on hinges; these take the place of the weather boarding. The interior wall is then arranged the same as the one at the opposite end of the room. These doors can be opened as the ice is coming out, and remain closed at other times. Interior partition walls are sometimes of value. It is thought they add to the durability of the house, and also effect a saving in wastage. In the majority of houses they are dispensed with. The construction of the roof will be found convenient and substantial, if the plans shown in Plate _B_ are followed. Light-colored roofing composition should be used, avoiding tar and gravel, or tin, as these both attract and absorb the heat. Gable roofs, with good shingles laid four or five inches to the weather, are the best roofs for ice houses. They are cooler and more durable than most composition coverings.