PE Architectural common mistakes
PE Architectural · Understand the traps and how to avoid them.
Computing a single demand (dead + live) and comparing it directly to an allowable or nominal strength, instead of writing out the governing ASCE 7 load combinations first - including the 0.6D + W uplift case on cantilevers, roof overhangs, and retaining walls.
Most candidates learned a one-line 'D+L vs. allowable' check in school and carry it in as a reflex; the exam scenarios are deliberately selected so that wind uplift or seismic reverses the governing case, and the simple sum never surfaces it.
What to do instead
Before touching numbers, list the 3–4 combinations that could plausibly govern for that element (usually 1.2D+1.6L, 0.9D+1.0W, and the ASD equivalents) and compute each. On any cantilever, roof member, or retaining wall, always run the minimum-dead-load-plus-wind case explicitly - it is the one that is missed.
Applying a live load reduction by subtracting a flat percentage or using the wrong area, without first computing the influence area KLL·AT and confirming the element is one for which ASCE 7 permits reduction (one-way slabs, and members supporting only one floor, are common traps).
Candidates remember that reduction exists and roughly how big it is, but not that the reduction is a function of tributary area times the element's live load element factor and that it is capped (no reduction below 50% of the unreduced load for members supporting one floor).
What to do instead
Always compute KLL·AT as a number, state the applicable element factor (KLL = 4 for interior columns, 2 for beams and exterior columns, etc.), and check the floor-count cap before using the reduced value. If the problem gives you a light floor system with a small tributary area, expect no reduction at all.
Sizing outdoor air by occupant count only, or by floor area only, rather than summing the per-person and per-area components and then dividing by the zone air distribution effectiveness.
Rules of thumb (e.g., '15 cfm per person') circulate widely, so candidates skip the dual-component ASHRAE 62.1 breathing-zone calculation and never apply the distribution effectiveness factor for the zone type, which changes the answer by 20–100%.
What to do instead
Set up the calculation as Vbz = Rp·Pz + Ra·Az, then Voz = Vbz / Ez, and state Ez for the zone (1.0 for well-mixed cooling-only, 0.8 for ceiling supply with ceiling return, etc.). Do the arithmetic symbolically first so units and components stay separate.
Confusing total heat with sensible heat when sizing a coil or an air handler, or using the 1.08/1.10 duct constants at a condition (altitude, wet coil, or high bypass) where they do not apply - then reporting a cfm that is off by the latent fraction.
The sensible-heat equation is the one candidates memorise, and exam items that give you total heat, apparatus dew point, or a design altitude look like the familiar problem but are not.
What to do instead
Before selecting a formula, label what the problem gave you: total or sensible. Use the sensible-heat relationship for temperature-only changes and the total-heat relationship for enthalpy changes. State that the 1.08/1.10 constants assume standard air (≈0.075 lb/ft³) at sea level, and adjust or note the limitation when the stem gives altitude or a wet-coil condition.
Building a panel schedule by summing connected loads without applying the code demand factors and the 125% continuous-load adder, or by mixing volt-amperes across 120 V and 240/208 V circuits as if they were additive current.
Connected load addition is intuitive and fast; demand factors, the continuous-load multiplier, and the difference between VA and amperes at different voltages require deliberate bookkeeping that candidates skip under time pressure.
What to do instead
Convert every load to VA and kVA at its own voltage before summing anything. Then apply the applicable demand factor for the occupancy, apply 125% to continuous loads, and only at the end convert to amperes at the service or feeder voltage. Show the demand factor as a separate line so the grader (and you) can see it was applied.
Computing voltage drop with the single-phase two-wire formula (2·K·I·L/CM) on a three-phase feeder, or using the one-way circuit length when the formula requires the round-trip length.
The single-phase form is the one most often memorised and the difference between it and the three-phase form (√3·K·I·L/CM) is a single constant that is invisible if you never write the circuit type down.
What to do instead
Write the circuit type - single-phase two-wire, single-phase three-wire, or three-phase - as the first line of the calculation, then pick the matching constant (2 or √3). Convert the length to the units the resistance or K value expects, and use the load current, not the breaker rating, unless the stem says to size for the breaker.
Computing occupant load from the gross floor area of the whole building shell instead of the net floor area of the specific use, and then failing to check that the egress width, exits, and travel distance are adequate for the occupant load of the room plus any occupants egressing through it from adjacent spaces.
Gross versus net area is a single word in the code table that candidates read past, and the 'egress through an intervening space' rule only appears in a small number of scenarios, so it is rarely practised.
What to do instead
For every space, state the use classification, whether the table calls for gross or net area, and the resulting occupant load as an explicit number. Where a room is a required exit path from another space, add those occupants to the room's own load. Then check egress width per occupant, number of exits, and travel distance against the values for that occupancy and sprinkler status.
Measuring travel distance in a straight line from the most remote point to the nearest exit door, and applying the sprinkler-increase allowance without first confirming the building is actually fully sprinklered per the code definition.
Travel distance looks geometric on a floor plan, and candidates measure the diagonal rather than the actual path around partitions; the sprinkler allowance is remembered as a bonus that can be claimed whenever sprinklers are mentioned in the stem.
What to do instead
Trace the actual path a occupant would walk, around corners and along aisles, and measure that path. State the base allowable travel distance for the occupancy, then state whether the increase applies and the code basis for it - a partial or 13R system does not qualify for the same allowance as a full 13 system.
Using unadjusted reference design values for lumber, or nominal rather than dressed dimensions, when checking a wood member - skipping the load duration, size, repetitive member, and wet-service adjustment factors.
Reference values in the NDS supplement are tabulated as clean numbers, and it is easy to read one off and compare directly to the computed stress without realising reference values are for standard duration, dry service, and a specific size.
What to do instead
Write the adjustment equation out in full (Fb' = Fb·CD·CM·Ct·CL·CF·Cfu, and the equivalent for shear and compression) and assign each factor a value with a one-word justification. Use dressed dimensions for section properties, and check the adjustment factors that actually differ from 1.0 for the given condition rather than listing all of them.
Answering a scheduling or contract-administration item with the 'standard' AIA A201 answer without checking which agreement, delivery method, or party the stem actually names - and computing total float as free float, or forgetting to re-sequence the critical path after a change.
Most candidates have seen far more A201-based examples than design-build, CM-at-risk, or owner-held-contract scenarios, so the default answer feels safe; float terminology is also easy to blur under time pressure.
What to do instead
Circle the delivery method, the contract type, and the party named in the stem before reading the options, and answer only from that arrangement. For network questions, compute early and late dates for every activity, label total float and free float separately, and redraw the network after any logic change before selecting the new critical path.