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Open to Below

Open to below is a note on an upper-floor plan marking an area with no floor, where the space opens down to the level beneath. Two-story foyers and great rooms with tall ceilings are common examples.

On the plan, the open area is usually outlined and crossed with an X or diagonal lines, with the words "open to below" written inside. A railing or half wall typically runs along the edge.

An open-to-below area is counted once, on the lower level that has the floor, and left out of the upper floor's square footage. A stair opening is not treated this way, since stairs count on the floor they descend from. See open-to-below areas in GLA.