An envelope plan is a delineation of the extent of a building’s mass taken at a fixed elevation. It establishes a precise limit to the outermost profile of the building. Envelope plans are easily derived from photogrammetric surveys and point clouds that decribe the exterior conditions of a building.
The value of the envelope plan should not be overlooked. When charged with creating plan drawings of a building, the envelope plan is the first place to start. It provides a reliable framework against which any data from an interior survey can be compared – significantly reducing the occurrence of human error when constructing a detailed floor plan drawings depicting interior layouts.
When possible, I use data from photogrammetry to prepare envelope plans before I go inside a structure to collect additional observations. By establishing accurate envelope conditions, previously mysterious internal conditions that might have been otherwise unmeasurable (such as wall thicknesses) can then be reliably calculated.
An envelope plan is especially valuable for non orthogonal structures. For some projects when I am collaborating with a team of architects who are close by to a project site, I prepare the envelope plan using photogrammetry and then hand it off to my colleagues who will complete the drawing during subsequent visits to the building. It is a great way to eliminate questions that arise amid a wealth of (sometimes) confusing field notes and measurements.