Building envelope

The building envelope is the three-dimensional legal volume within which a building must fit, produced by the interaction of the district's bulk rules: yards shrinking the footprint, coverage capping it, base heights and setbacks shaping the profile, and a maximum height or sky exposure plane closing the top. The envelope is distinct from the floor-area budget — FAR says how much may be built, the envelope says where it may stand.

Envelope analysis (massing) is the discipline of packing the budget into the volume. When the budget fits easily, FAR governs; when the envelope binds first, paper floor area goes unbuilt. Most surprises in buildability trace to the envelope, not the ratio.