Space surfaces can be configured for surface type. For example, a wall can be interior or exterior, and a floor can be interior, slab, or underground. However, you do not need to specify surface types in order to use the gbXML export tool. The tool automatically figures out the correct surface type when the gbXML file is created. For example, surfaces that have no adjacent spaces are considered exterior, and wall surfaces below grade level (z = 0) are considered underground. You can specify surface types in the Space/Zone Manager.