Doors are edges in a graph.
Who This Matters To (And Why)
Critical: Architect (doors define circulation paths and egress compliance), GC (door installation is a significant trade scope with precise sequencing requirements), Engineer (doors in rated assemblies require specific coordination with structural and fire systems).
Important: Developer (door count and hardware specification affect hard costs), City (egress door compliance is a primary plan check item).
Context: Banker, Broker, Inspector.
Highest typology impact: Multifamily, Office, Hotel — high door count buildings. Lower impact: Industrial, Open retail.
Doors are edges because they are the connections between nodes in the building's spatial graph. Every door represents a potential path between two rooms. The door's properties — rated assembly, hardware, clearance — are properties of the connection, not the door leaf itself.
How It Shapes Development
The building's circulation graph is defined by its doors. Walk from the entry to any room and you pass through a sequence of doors. Each door is a node in the path. The set of all possible paths between all room pairs defines the building's accessibility structure. A building where the path from a parking space to a dwelling unit passes through three doors, two elevators, and one fire stair is less accessible — and less marketable — than one where the path passes through two doors and one elevator.
Egress path analysis is graph traversal. The code question “can every occupant in this room reach an exit within the allowed travel distance?” is a shortest-path problem on the building's door graph. The occupant is a node. The exits are destination nodes. The maximum allowed travel distance is the edge weight limit. Code compliance is verified by confirming that a path exists from every occupied room to an exit within the allowed distance. This is graph theory, not architecture theory, which is why it can be computed.
Fire door requirements are edge properties in the code graph. When a corridor is required to be fire-rated because it separates a high-hazard occupancy from egress, every door in that corridor wall must be fire-rated to match the assembly. The door is a break in the rated assembly. An unrated door in a rated assembly defeats the assembly's purpose entirely. The door rating is a property of the edge — the wall-to-corridor transition — not a property of the door in isolation.
Accessible door requirements are dimensional constraints on edges. A door providing accessible passage must have a minimum 32-inch clear width when open (36-inch nominal door). The hardware must be operable with one hand without tight grasping. The threshold must not exceed 3/4 inch. These requirements apply to doors that serve accessible routes — which is most doors in any building that serves the public. The accessible route is a subgraph of the full door graph, with stricter edge property requirements.
Door hardware specification is where the detail lives. The hardware set includes hinges, lockset, closer, and any required coordinator, astragal, or security hardware. Hardware sets must be coordinated with door and frame types, fire ratings, accessibility requirements, security requirements, and operational preferences. A typical multifamily building might have 8–12 distinct hardware sets for its 200–400 doors. The door hardware schedule is a table that assigns each door instance to its hardware set and ensures consistent specification. It is one of the most complex coordination documents in a construction package.
Quick Wins: Connect This Applet To
- Applet #41 (Egress Is a Shortest-Path Problem): Direct pair. Show egress path from each room through door connections to exit. Input travel distance, show pass/fail for each room. One distance input, one room-by-room pass/fail output.
- Applet #32 (Schedules Are Just Graphs): Door schedule generator. Select door type from graph properties, populate schedule row. Door type dropdown, one schedule row output.
- Applet #28 (Adjacency Is the Only Spatial Rule): Show that wherever two rooms are adjacent, a door is possible. Show that wherever egress requires passage, a door is required. Adjacency input, one door requirement readout.
For Other Professions (24-Hour Builds)
- GC: Add door count-to-cost estimator. Show rough material and labor cost for a building's door package by door count, frame type, and hardware complexity. Three inputs, one cost estimate.
- Inspector: Add egress door compliance checklist. Show the most common egress door deficiencies found during inspection. Static list, one deficiency frequency display.