Core competencies for safe, functional, and innovative design practice
This domain is where IDPX separates people who can draw from people who can be trusted with a permit set. Items are scenario-based: you get a tenant fit-out, a change order, or a plan with a conflict buried in it, and you must pick the response that protects life safety, preserves accessibility, coordinates the consultants, and stays inside the contract documents. Expect quantitative egress work, accessibility dimensions, finish and fire-resistance classifications, and questions about the interior designer's authority during construction.
Core rules to hold
- Egress is a chain: occupant load → number of exits → capacity (width) → arrangement (remoteness, travel distance, dead ends) → discharge. Break one link and the plan fails.
- Occupant load = area ÷ load factor. Business and mercantile use gross area (mercantile 60 gross); assembly and standing space use net. Always round fractions up.
- Sprinklered buildings use 0.15 in of egress width per occupant at corridors and doors and 0.2 in at stairs; unsprinklered rises to 0.2 and 0.3.
- Most occupancies need two exits once the calculated load reaches 50, separated by at least half the diagonal of the area served (one-third where fully sprinklered).
- Accessibility floors: 36 in clear route, 32 in clear door leaf, 60 in passing spaces, controls 15–48 in above finish floor.
- Exit enclosures take Class A wall and ceiling finishes; sprinklered corridors may drop to Class B.
Worked example
A sprinklered mercantile tenant has 6,000 sq ft of gross sales area. 6,000 ÷ 60 = 100 occupants. Because 100 ≥ 50, two exits are required, and they must be separated by at least one-third of the diagonal. Capacity is 100 × 0.15 = 15 in total, but each door still needs 32 in clear, so two 36 in doors govern - the calculation never overrides the minimum. A single 72 in storefront opening meets raw width yet fails remoteness and independent paths.
Traps that cost marks
Using a net factor on gross area; letting calculated width override minimum clear width; assuming sprinklers waive exit count (they only reduce remoteness); treating a submittal as "approved" when the designer reviews and returns comments; and answering a code question with a design preference.