Chapter 9 — Quiz

B. Water first — a bulk-water failure destroys an assembly quickly and expensively. Air second, because air leakage carries both energy and moisture continuously. Vapor third, because diffusion acts slowly and seasonally. Thermal fourth: it costs operating money and creates condensing surfaces, but a thermal defect does not rot a wall by itself.

C. The cladding is a screen: it sheds most of the water and takes the sun and wind. The system assumes water gets past it. The WRB behind the cavity is the actual water control layer, and the cavity plus flashing and weeps give the water a way back out.

C. $5,150/CD of extended general conditions plus $5,500/CD in liquidated damages to Meridian Health System.

B. 14 − 6 = 8 CD chargeable × $10,650/CD = $85,200. Answer C is the number most people quote (14 × $10,650) and it ignores float. Answer D is the mistake in the other direction — float absorbs part of the slip, not all of it, and consuming float has its own cost.

C. 38 weeks: shop drawings (6), review (3), resubmittal and re-review (4), material procurement (10), fabrication (12), with shipping and staging partly overlapped. Field installation is another 11 weeks after that. This is why curtain wall usually has to be bought out within about six weeks of Notice to Proceed.

C. Tapered insulation provides slope (A), a separate sheet provides the vapor retarder (B), and the cover board contributes little R-value (D). The cover board resists foot traffic, hail, and dropped tools, stabilizes the adhesive substrate, and is frequently required by the assembly's fire and wind-uplift listings. Deleting it saves roughly $1.10–$1.60/SF and endangers the warranty.

B. NDL means "no dollar limit," and it covers labor as well as material. It is issued by the manufacturer, not the subcontractor (C), terms vary (A), and it absolutely can be voided (D) — by unapproved components, missed manufacturer inspections, or post-occupancy alterations by others.

B. The overwhelming majority of sealant failures trace to the substrate: dusty, damp, cold, or contaminated surfaces, and the wrong primer or no primer. Three-sided adhesion (no bond breaker) is the second most common. UV degradation is real but slow, and undersized — not oversized — joints are the geometry problem.

C. A ±25% sealant can stretch or compress a quarter of the joint width. To absorb 0.25 inches, the joint must be at least 1.00 inch wide. Building it at ¾ inch because it looks better is designing a failure.

B. The in-wall inspection comes after rough-in and blocking and before insulation and board; the above-ceiling inspection comes after overhead MEP and before ceiling tile. Each is a gate, not an activity — it cannot be partially complete, and a failure stops the whole zone.

C. A rated wall must be continuous through the plenum to the deck above, with a detailed head-of-wall joint that accommodates deflection. A wall that stops at the ceiling is a decorative partition with a red line on the life-safety plan. Some rated ceiling assemblies exist as tested systems, but they are specific listed assemblies — not a lay-in tile ceiling.

C. Level 5 exists for critical lighting and glossy paints, where Level 4's joint compound over tape reads as visible banding. Tile substrate is Level 2, concealed plenum surfaces are Level 1, and fire rating is a function of the assembly, not the finish level.

False. Industry rules of thumb put it at roughly thirty to fifty times the installed cost, because the repair requires either excavating a finished building or accepting a permanent negative-side compromise.

False. The field is a large welded sheet installed by specialists and rarely fails. Leaks concentrate at the perimeter and at penetrations — Northgate has 214 of them — because those require judgment, sequence, and a second trade.

False. Curtain-wall units are designed to accept some water past the outer seal and drain it back out through an internal sill gutter and weeps. Water at the slab usually means the drainage path is blocked or misdirected — commonly a crushed end dam or a blocked weep — not an exterior seal failure.

False. A mockup tested after fabrication starts is not a quality-control tool; it is an expensive way to discover a recall. The test and its report belong on the critical path in front of the fabrication release.

False. A change in SHGC or U-factor is a mechanical load decision, an energy-code compliance decision, and a schedule decision. Route glazing substitutions to the mechanical engineer before anywhere else.

False. Enclosure is achieved by area. On Northgate, Margo issued a written partial enclosure release for Levels 1 and 2 on February 3, Year 2, and framing started February 5 — seven weeks before the March 28 whole-building milestone.

A control layer is only as good as its worst interruption. Air leakage follows the path of least resistance, so a small continuous gap moves a disproportionate share of total flow. Water is worse because it concentrates: a large collection area drains toward one bad seam. The field of a wall is repetitive work done well by people who do it all day; transitions require judgment and usually involve two subcontractors, so that is where failures live.

Three examples: wall-to-foundation — the above-grade WRB and the below-grade waterproofing are different materials installed by different trades, and the classic failure is water entry at the base with no through-wall flashing or weeps. Wall-to-roof (parapet) — the wall air barrier stops at the top of the sheathing and the roof membrane stops under the coping, and nothing connects them over the top. Window-to-wall — three trades touch one rough opening; failures are reverse laps at the head, a missing sill pan, and crushed end dams.

A face-sealed wall stops 100% of the water at the exterior surface, relying on a single permanent line of defense made of materials that move and age at different rates and are installed outdoors by hand. One failure delivers all the water inside.

A rainscreen assumes failure. The cladding blocks most of the water; what gets past lands in a drained, vented cavity and runs down to a through-wall flashing that returns it to the exterior through weeps. The venting does a second job: it lets the cavity's air pressure equalize with the exterior. Wind-driven rain is pushed through openings by a pressure difference — remove most of the difference and you remove most of the driving force.

The mechanism is redundancy, not perfection. You cannot build a perfect wall with imperfect people in bad weather; you can build one that keeps working when a piece of it fails.

(a) The water control layer fails through a reverse lap. Water draining down the outside face of the WRB meets the top edge of the flashing membrane, which faces uphill, and runs behind the flashing and into the wall. Because the WRB is also the air barrier on this assembly, the air layer fails at the same plane, and the thermal layer degrades locally when the mineral wool wets. Vapor is not the issue — this is bulk water.

(b) Not at the window. Water runs down the back of the frame, into the stud cavity, and appears as staining at the base of the wall below the window or at the first horizontal obstruction. The leak begins with the first wind-driven rain and is invisible; visible interior staining typically shows at eight to fourteen months, sheathing deterioration and mold at two to four years.

(c) First: the factual statement of the conflict citing all governing documents — 4/A-501 versus 2/A-321 and Spec 07 27 00 — so the order of precedence can resolve it. Second: the dated schedule-impact sentence — "WRB installation at the north wing begins in 12 work days; a response after that date will require a resequence of the exterior envelope work." That sentence converts a technical question into a documented notice, and it is worth more than the rest of the RFI if this ever becomes a dispute.

(d) Roughly $0 now (a revised sequence card and about $340 of soft cost) versus $486,300 in warranty — 74 openings at about $5,950 each for flashing, cladding removal and reinstallation, swing stage, interior repair, and consultant share, plus a $46,000 investigation. Between those endpoints: $1,200 at the mockup, $8,160 after the first twelve openings, $217,560 after cladding but before occupancy.