The posts in Diagram _B_ can be extended and additional bracing put in. The increased area and weight will require a proportional addition to the strength of roof timbers. In the sizes of timbers for ice house construction, noted in this chapter, consideration has been given to durability, and while lighter material is employed, in some instances, the houses are sooner racked and sprung out of place. [Illustration: FIG. 50. PLATE _C_. SECTION OF ELEVATOR INCLINE AND PLATFORM CONVEYORS.] The ventilator on top is about twenty feet square and two feet high, with slats on all sides. It will not be required on high gable roofs, an opening in each gable end being sufficient to carry off the moisture and heated air. The gable ends should be well braced against the wind. At the center of roof trusses a floor is laid through the building, dividing the space above the ice. Trap doors are cut through this floor about seventy-five feet apart, four to six feet in size; these doors are for ventilating the space between the ice and the floor, and for dumping the sawdust through on top of the ice. It also affords a convenient place in which the sawdust can be stored and dried, when the houses are cleaned in the fall. The outer circulating air-spaces are continued to the level of the loft floor, discharging the air into the loft, where it finds vent through the ventilator. The eaves project about two feet, and are provided with ample gutters, which are furnished with large conductor pipes every fifty feet. On the side of the house where galleries are placed, the roof is extended to cover them, or, if at a gable end, a special roof is provided. Lightning rods are especially required on ice houses. Being often the most prominent object in their locality, the electric fluid finds its readiest path through them, and the escaping vapor and much of the material used in their construction add to their exposure. Copper strips, terminating in forked points, raised above the cone of the roof, fifty or seventy-five feet apart each way, provide ample protection. A line of points across the house should be connected, and the copper strips extended, without any break or interruption, into the ground. They should be buried several feet below the surface, and if they terminate in a drain or other damp place, their efficiency is increased. [Illustration: FIG. 51. ELEVATION OF PLATFORM ALONG TRACKS FOR LOADING CARS.] [Illustration: FIG. 52. PLATE _D_. SECTION OF LOADING PLATFORMS.]