Is the bottom of building flat or round?

Question

Is the bottom of a building flat or round? Obviously the building is on the Earth, and the Earth isn't flatten. The use a grader and other tools to prepare the ground for the building though. Is that prepared ground flat, or the surface of sphere. More importantly, how much land would a HUGE building have to cover before the people building it had to worry about the difference?

Answer 1

Buildings are usually made "level", which means they follow the curvature of the earth and are therefor not "flat", but one would be hard pressed to measure the difference in most buildings.
Since buildings are usually made of a number of relatively small pieces the difference in length in any given piece caused by the curvature is usually less than the tolerances for fabricating the part, so I believe the effect of the earths curvature is usually ignored. In some cases there are very long continuous structural elements (suspension bridge cables) and the effect of curvature may be noted, but I doubt anyone "worries" about it much, as again, normal tolerances (not to mention thermal effects) make a bigger difference.

Answer 2

Buildings are made level (flat). Even the largest building in the world, in Everett, WA, where Boeing manufactures planes, at several Acres of area is a flat, level surface. If I recall correctly it is one of the most level concrete surfaces in the world.

However, there are some structures that require building to the curvature of the earth. For example, the Washington suspension bridge over the Hudson river has 2 towers. Normally you'd think they'd be parallel with each other, but they are not. They are laid in perpendicular to the ground where they are standing. The base of the towers is some distance, but the top of the towers is greater than the base distance by several inches (IIRC) due to the curvature of the earth. This would apply to all long suspension bridges, too.

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