17.2 Common Pitfalls & High-Yield Topics

Where to Spend the Final Hours

Not all domains are equal. Three domains carry the heaviest weighting and should absorb the majority of your final review time: IDIX Domain III (Construction Documents) at 32 percent, IDPX Domain III (Contracts, Procurement, Permitting) at 28 percent, and IDFX Domain VI (Design Schematics) at 20 percent. If you have only one evening left, drill these three. The bar chart below shows how they tower over the remaining domains.

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IDIX Construction Documents (32%) — High-Yield Pitfalls

This is the single largest domain on the exam. Frequent mistakes include:

• Drawing-set coordination. The floor plan, RCP, and demolition plan must align. A wall moved on the floor plan but not the RCP is a coordination error the exam will test.
• Scale and notation consistency. Demising walls, rated assemblies, and fire barriers must be consistently hatched and labeled across every sheet; the legend defines the convention.
• Demolition plan conventions. Existing-to-remain is hatched; demolished elements are dashed or crossed out. Confusing the two is a classic distractor.
• Construction plan vs. floor plan. The construction plan shows new work; the floor plan shows the overall layout. Items belong on one sheet, not both.

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IDPX Contracts, Procurement, Permitting (28%) — High-Yield Pitfalls

This domain is heavy on contract documents and delivery methods. Memorize these distinctions.

Fee Structures

Delivery Methods

• Design-Bid-Build (DBB): separate design and construction contracts; low-bid selection; owner controls design; slowest.
• Design-Build (DB): single entity; fast-track; owner loses direct design control; one point of responsibility.
• CM-at-Risk (CMAR): CM converts from advisor to constructor at the GMP; owner holds two contracts early, consolidating later.
• CM Agency: CM is the owner's advisor; trade contracts are held directly by the owner.

Change Document Family (AIA)

• G701 — Change Order: formal, signed by owner, architect, and contractor; finalizes a change to contract sum and time after agreement.
• G714 — Construction Change Directive (CCD): architect directs the contractor to proceed before cost/time is agreed; reconciled later by a G701.
• G710 — Architect's Supplementary Instructions (ASI): the architect's minor clarifications or changes that do not adjust the contract sum or time; no pricing agreement is required.

A bulletin is the informal predecessor — a notice of a proposed change with no contract effect. The escalation order is bulletin → ASI (G710, minor/no-cost changes) or Construction Change Directive (G714, work directed before cost agreement) → Change Order (G701), shown in the diagram below.

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Frequently Confused Pairs

Travel Distance Limits (IBC 2021, representative)

• Unsprinklered, Business (B): roughly 200 ft exit access travel distance.
• Sprinklered, Business (B): roughly 300 ft (an NFPA 13 sprinkler extends the limit).
• Limits vary by occupancy and construction type — always confirm against the provided IBC on exam day using the index, not memory.

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IDFX Design Schematics (20%) — High-Yield Pitfalls

• Concept refinement must respond to the program, not aesthetics alone. A schematic that drops a programmed space is wrong even if it looks elegant.
• Code review begins in schematics, not CDs. Occupancy classification and occupant load are schematic-phase deliverables.
• Visualization — orthographic, axonometric, perspective — must match the audience: clients get perspectives, contractors get orthographics.

Pair the heaviest domain (CDs) with the most procedural domain (Contracts) and the most conceptual (Schematics), and you cover roughly 80 percent of the weightiest exam content in one focused pass.

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A Worked Code-Calculation Pitfall

The occupant-load-versus-plumbing-fixture confusion is the single most common code calculation error. Walk it once carefully.

A two-story office (Group B) has 12,000 gross sf per floor. Per IBC Table 1004.5, Business occupant load is 100 sf gross per occupant, so each floor yields 120 occupants, 240 total. That occupant load drives two separate downstream numbers and must never be conflated with either:

• Egress width (IDIX life-safety): stairs at 0.3 in. per occupant = 72 in. minimum stair width for the 240 occupants; level egress doors at 0.2 in. per occupant = 48 in. minimum.
• Plumbing fixtures (IDIX specs): per IPC Table 403.1, Business requires 1 water closet per 25 occupants of each sex (split 50/50 unless otherwise shown). 120 males ÷ 25 = 4.8, rounded up to 5 water closets; 120 females ÷ 25 = 5 water closets. The calculation always rounds up to the next whole fixture.

The trap is using the occupant load number as the fixture count, or rounding the egress width down instead of the fixtures up. The two calculations share an input (occupant load) but use different tables, different units, and different rounding rules. On exam day, look up each table separately by keyword in the provided IBC and IPC; never carry one table's result into the other calculation.