For moderate heights the walls can be self-sustaining, that is, built up solidly; but beyond a certain height it becomes economical to use curtain walls similar to the well known “skyscraper.” In buildings up to eight stories, reinforced concrete frame with monolithic floors prove more economical than steel frame with tile or concrete floors. Reinforced concrete buildings are more lasting, since it is impossible to closely fit tile around steel columns and girders and exclude air, moisture, heat and condensation, existing in this class of building, conditions most contributing to rust. The life of steel framing under these conditions is an untried experiment. On the other hand, in the reinforced concrete building the strength is much derived from the concrete and when well designed and the work well executed the steel is imbedded and thoroughly concealed in the concrete, remote from the conditions above stated and contributing to an indefinitely long life. However, steel columns and girders encased in concrete make them practically the same. _Limit for Economic Concrete Columns._--Eight-story warehouses with basement appear to be ample in height for ordinary conditions. Meeting the insistent demands of building ordinances in some cities like Chicago, these can be constructed of reinforced concrete with a maximum column diameter of twenty-eight inches, with all floors designed for 200 pounds per square foot. This height of building with such loadings approximates the practical limit of sustaining on footings on the usual underlying earth, with building panels sixteen feet square, the column spacing best adapted to storage purposes. _Types of Construction._--In concrete buildings just referred to, our preference in style of construction is either of the mushroom type, that is, flat ceilings without girders; or secondly, with girders extending in one direction only. An inexperienced engineer in his efforts to minimize the quantity of steel and concrete requirement will invariably wish to carry girders from column to column and cross beams between girders, making the ceiling look like a checkerboard, losing perhaps twenty inches or more head room on every story and making a much more expensive building to construct and operate. The same fault is noticeable in steel frame buildings, since nearly always there are cross beams between girders. This drops the chilling pipes, curtailing head room and makes an unsatisfactory arrangement. Whereas with a mushroom or flat ceiling with girders in one direction, the difficulty is overcome. _Space Losses; Beams Two Directions._--In an eight-story building the additional height above referred to amounts to from ten to fifteen feet of unnecessary building and adds greatly to the construction cost.