24-Bld-A7 Building Envelope Design · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Reference texts: Straube & Burnett, Building Science for Building Enclosures; ASHRAE Handbook — Fundamentals (Ch. 25 Thermal and Water Vapor Transmission Data, Ch. 26 Heat, Air, and Moisture Control in Building Assemblies); National Building Code of Canada (NBCC), Part 5 (Environmental Separation); ASTM C1472, Standard Guide for Calculating Movement and Other Effects When Establishing Sealant Joint Width; CMHC Best Practice Guides for Building Envelopes (brick veneer, shelf angles, thermal bridging, movement joints, flashing). This is a closed-book paper; the exam instructs that only the first five questions as they appear in the answer book are marked, but every question found in the source is answered in full below as a complete study resource.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Each statement turns on a specific building-science mechanism — independent vapour/air drivers, condensation physics, wind-pressure zoning, or hygrothermal material behaviour — rather than rote recall. Statements 2 and 11 are each printed as two distinct sentences run together; both halves of each are evaluated below and a single combined verdict given, since the exam prints them as one numbered row.
1. FALSE. Vapour diffusion is driven by the vapour-pressure gradient (Fick's law, Eq. 1 of the appendix), while air leakage is driven by the air-pressure gradient (stack effect, wind, fan pressurization). The two drivers are independent, so a wall can diffuse vapour in one direction while air leaks through it in the other.
2. TRUE (both clauses). Condensation on any cold surface — including inside the wall assembly, wherever a surface drops below the local dew point — wets the material and promotes mold growth if conditions persist; separately, a window's overall R-value/U-factor is a certified whole-unit property (NFRC/CSA A440) in which frame material, frame-to-glass ratio and edge-of-glass effects all matter, not the glazing alone.
3. FALSE. Wood's moisture-induced dimensional change is smallest along the grain (longitudinal, ≈0.1–0.3%) and largest across it (tangential, then radial) — the statement names the wrong direction.
4. FALSE. Vapour-barrier placement is climate-dependent: an indoor-side vapour barrier suits a heating-dominated (cold) climate, but in a cooling-dominated or mixed/humid climate it traps outward-diffusing moisture against the cool interior finish, causing the very damage it is meant to prevent — "any climate condition" is the false part.
5. FALSE. Wind pressure/suction coefficients (NBCC/ASCE 7 tables) differ sharply by surface and zone; corner and roof-edge/corner zones see the highest local suctions (conical vortex effects), typically 2–3× a field-of-roof or field-of-wall value — roof suction from wind over the top and wall-corner suction are not equal.
6. TRUE. Brick ties (wall ties) transfer out-of-plane wind (lateral) load from the veneer wythe back to the structural backup wall, while permitting the small differential vertical movement between veneer and frame.
7. TRUE. Mold-growth models (e.g. Sedlbauer isopleth curves) show risk depends on the combination of relative humidity, temperature, AND the duration those favourable conditions persist — a brief excursion above the mold-growth RH threshold is far less risky than a sustained one.
8. TRUE, as far as the printed text goes. The clause given is the standard operating definition of a vapour barrier's function (retarding, not fully stopping, diffusive moisture transport); the sentence is cut off before its likely conclusion (continuity/placement requirement), so no verdict is offered on the missing portion.
9. TRUE. Unlike a vapour barrier, an air barrier has no required position within the assembly (interior, exterior, or mid-wall are all valid) provided it is continuous, air-impermeable and structurally supported to resist the design wind/stack pressure.
10. TRUE. This describes the exterior-air-barrier ("smart"/perfect-wall) strategy: an air/WRB membrane on the cold side of the insulation must be substantially more vapour-open (roughly an order of magnitude, 10–20×) than the interior vapour retarder so that any incidental moisture reaching the sheathing can dry outward rather than being trapped between two vapour-tight layers.
11. FALSE (first clause governs). Mortar's job is to bond and transfer load between masonry units and accommodate minor construction tolerances; brick veneer is explicitly not treated as watertight at the mortar joints — bulk rainwater is managed by the drainage cavity, flashing and weeps behind the veneer, not by a mortar "seal", so the first sentence is false. The second clause (temperature-driven air-density differences causing stack effect, which promotes air leakage) is a correct, standard definition on its own; because the row asks for one verdict and the false first clause is the operative claim, the combined statement is marked FALSE.
12. FALSE. In cold weather, stack effect makes warm, buoyant indoor air rise: air exfiltrates near the top of the building and infiltrates near the base, i.e. the net internal air movement is generally upward, not downward.
14. TRUE. In a metal/glass curtain wall, thermal bridging through the frame plus a convective loop within the sealed IGU cavity make the bottom edge/rail of the glazing the coldest, most condensation-prone location in practice — any moisture that does condense also drains down and collects there.
15. FALSE. The optimum sealed-cavity width differs by fill gas because krypton's lower thermal conductivity suppresses convection at a narrower gap than argon needs: argon's optimum is roughly 12–16 mm, while krypton's optimum is narrower, near 6–10 mm — using argon's optimum spacing with krypton wastes its performance advantage.
16. TRUE. For hygroscopic materials (wood, OSB, plywood, wood-fibre board, gypsum), vapour permeability rises — often by an order of magnitude or more — as ambient relative humidity increases, because sorbed moisture opens additional diffusion pathways through the material's pore structure.
17. TRUE. Corners restrain a brick veneer wythe in two directions simultaneously and concentrate thermal/moisture movement demand, so a missing movement (expansion/control) joint at or near a corner is a classic cause of distress (cracking, spalling) in brick veneer.
18. FALSE. A thin air-barrier membrane is not thick enough to add meaningful thermal resistance — it can genuinely serve as an air barrier, a WRB, and (if its own permeance is low enough) a vapour retarder, but it cannot also function as the thermal insulation layer. (Contrast: a thick, taped rigid-insulation board genuinely can multi-function this way — the subject of the statement, membrane vs. board, is what decides the verdict.)
19. TRUE. In sloped roofs, thermal bridging through rafters/purlins and wind-washing (air movement through or around loose-fill/batt insulation, especially near the eaves) both degrade the effective in-service R-value, so the assembly's overall U-factor is more likely to be higher than the nominal insulation R-value alone would suggest.
20. TRUE. Argon has a lower thermal conductivity than air; filling the sealed IGU cavity with argon in place of air raises the cavity's thermal resistance and lowers the unit's U-factor (raises RSI).
