The Project Loose Geometry Tool allows you to use the native SketchUp tools to draw loose geometry onto surfaces of your building envelope. When you are ready to project these surfaces into the spaces of your model, you can open this tool and run it across all loose geometry or the selected loose geometry. Although this is often used to create fenestration, it can also be used to split a base surface into two base surfaces. For example, you can create a line 3 feet above the ground representing a change in construction from concrete block to brick. The advantage of this tool--versus the traditional method of entering and drawing within a space--is that you can quickly create surfaces across many spaces without having to ever enter those spaces.If some of the surfaces you have selected are not in the same plane as a building surface, they will be ignored.