OBC House Exam common mistakes
OBC House Exam · Understand the traps and how to avoid them.
Treating the occupancy classification as a single label chosen by building use, then applying one chapter's requirements without checking whether the space needs a mixed-occupancy analysis or an accessory-occupancy exception.
Candidates memorize occupancy group names and then jump straight to height/area tables, skipping the threshold questions (is the space accessory, is it separated, does the incidental-use table apply) that determine which rules actually govern.
What to do instead
Before answering any occupancy question, write down three checks: the use of each space, the area and fire-separation relationship between spaces, and whether the code treats the smaller space as accessory or incidental. Only then select the governing table.
Applying the base allowable-height and allowable-area table values directly to a building without applying the frontage increase, sprinkler increase, or the correct construction-type limits first.
The tables are the most visible numbers in the code, so candidates stop there and forget that the tabular values are a starting point modified by several adjustments applied in a defined order.
What to do instead
Work the height/area problem as a fixed sequence: determine construction type, read base values, apply the frontage increase, then apply the sprinkler increase, and check each intermediate result. Practice the full sequence rather than recalling final numbers.
Sizing egress components from the occupant load of the room being served without recalculating the occupant load of the floor or the story, and without checking the egress-width and exit-access rules that apply at each point along the path.
Questions often describe one room, so candidates compute one number and apply it to doors, corridors, and stairs alike, missing that the required capacity changes as occupants merge along the path.
What to do instead
Draw the egress path as a line from the most remote point to the public way and label the cumulative occupant load at each segment. Size each component for the load it actually serves, and separately verify number of exits and travel distance.
Assuming a fire-rated assembly's rating alone satisfies the requirement, without verifying the assembly's listing, the firestopping at penetrations, and the protection of openings in that assembly.
Candidates learn rating numbers (1-hour, 2-hour) as facts and treat them as the whole answer, forgetting that ratings are meaningless without listed assemblies and protected penetrations and openings.
What to do instead
For every fire-resistance question, answer three sub-questions: what is the required rating, is the assembly a tested/listed configuration, and are penetrations and openings protected to the required rating. Treat a missing sub-answer as an incomplete answer.
Confusing prescriptive envelope requirements with the performance or trade-off path, and mixing values from both approaches in a single answer.
Both paths are presented in tables that look similar, and candidates grab the first U-factor or R-value they recognize without confirming which compliance path the question describes.
What to do instead
Read the question stem for the compliance path before touching any table. State the path explicitly in your scratch work, then pull only values from that path's tables and verify units (U-factor versus R-value) before selecting.
Answering accessibility questions from general memory of clear-width and grab-bar numbers instead of applying the specific scoping rule that determines whether and where the requirement applies.
Dimensional values are easy to memorize, so candidates skip the scoping step (what elements, how many, which exceptions) and apply a number to a situation the code does not actually cover.
What to do instead
Split every accessibility question into scoping (does the requirement apply here, and to how many elements) and technical (what dimensions). Answer the scoping question first and cite the exception if one applies.
Selecting a foundation or structural system based on soil description alone, without checking groundwater, frost depth, bearing capacity, or the load path from the superstructure.
Candidates focus on the visible soil type named in the stem and treat foundation choice as a lookup, ignoring the site and loading conditions that actually drive the decision.
What to do instead
For foundation questions, list the four governing inputs (soil/bearing, groundwater, frost depth, loads and load path) and eliminate options that fail any one of them before choosing among the survivors.
Treating the building envelope as a single barrier and answering weatherproofing questions with one control layer, rather than locating the water, air, vapor, and thermal controls in the correct order within the assembly.
Candidates learn 'the barrier' as a concept and do not practice placing each control layer relative to the others, so they accept answers that put the vapor retarder or air barrier on the wrong side.
What to do instead
For each wall or roof question, sketch the section and label the four control layers and their positions. Check that the air barrier is continuous, the water control layer is drained and shingled, and the vapor control is on the correct side for the climate.
Reading inspection and plan-review questions as isolated facts about a test or document, without connecting them to the sequence of inspections and the point in construction at which each verification must occur.
Candidates study testing methods and plan-review checklists separately, so they miss questions that turn on timing, who must observe, or what must be approved before work is covered.
What to do instead
Build a timeline of the project from permits through final inspection and place each test and approval on it. For any inspection question, first identify the construction stage, then the required verification at that stage.
Answering mechanical, electrical, and plumbing questions by recalling equipment capacities or fixture counts without confirming the design basis (occupant load, demand factors, ventilation rates, or available pressure) that the question supplies.
MEP content is formula-driven, and candidates memorize outputs rather than the inputs, so they apply a remembered number even when the stem's occupancy, area, or demand conditions differ.
What to do instead
For every MEP question, extract the given design basis into a short list before calculating, then apply the method to those inputs. If a needed input is absent, treat the answer as unverified and reason from the governing principle instead of a memorized value.