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How does the height of the terrain relate to the height of my floors?
In the real world, floor platforms are nearly always built so that you step up into a building. There are a number of reasons for this, but perhaps the most important is to prevent the structure's framing from coming into contact with the terrain. Over time, exposure to moisture in the soil can damage or even ruin untreated lumber in a framed floor platform or wall. For this reason, building codes in most areas require that floors be raised off the terrain.
Chief Architect programs raise the building pad off the terrain for you automatically. The amount that the building pad is raised depends on the type of foundation you have built in your plan: