Every trade has its canonical gaps. Estimators who have written a hundred concrete scopes know what concrete subs habitually exclude; estimators who have written one or two do not. The remainder of this chapter is a field catalog of the gaps mentioned most often across the interviews, organized by trade family. None of this is exhaustive. It is the starting checklist.
Site and earthwork
- Geotech compaction percentages and lift requirements live in the geotech report, not the drawings. If the estimator works from the drawings only, they will be missed. Always upload the geotech.
- Tree protection, clearing and grubbing, erosion and sediment control — frequently in notes pages, easy to drop in revised drawing sets.
- The five-foot transition. Where does the site-servicing contractor stop and where does the plumber pick up? “Five feet outside the building” is the canonical answer in many markets; spell it out anyway.
- Excavator unit-rate exploitation. A Top-ENR Pre-Con Lead described a $5/m³ excavation quote that did not include trucking of unsuitable material. On a 10,000 m³ site this was a cripple-the-job miss. State explicitly that the unit rate includes trucking and dumping of all material types.
- Granular base under slab. Often weeping tile is excluded by civil and assumed by Division 3. Define it.
Concrete and cast-in-place
- Grouting under base plates. The canonical orphan. Formworker excludes (“he'll come back later”), steel erector excludes, GC self-performs by default. Name it in one scope or the other.
- Housekeeping pads, equipment pads, transformer pads. Frequently shown only on architectural or mechanical, not structural. Capture them anyway.
- Slab assembly conflicts. Architectural says 6″ stone + 4″ concrete; civil/structural says 4″ + 4″. Across 300,000 sq ft this is a $45K decision. Resolve at RFI, not at award.
- Building concrete vs. site concrete. In some markets one sub, in others two. Match your package structure to the local market.
- Sealers, hardeners, oil-float finishes shown on the room-finish schedule. Live in the finish schedule, not the structural set. Add them inferentially.
- Concrete pumping and hoisting. Inferred; often missed.
Structural steel and miscellaneous metals
- Embeds, anchor bolts, leveling plates. Whose scope — steel, concrete, precast? Spell out supplier and installer for each.
- Hoisting, rigging, manlifts for erection. Inferred. Always state.
- Miscellaneous metals scatter. “Misc metals got the most particular items scattered through the entire disciplines of drawings from the site works to the architectural, to the structural, to the electrical and the process” (Director at a Canadian Industrial/Process GC). Bollards, lintels, ladders, stanchions, pipe supports, dock ramps, generator yard platforms, UPS room railings.
- Stainless steel railings, glass balustrades. Often defaulted to misc metals but specced for glazing. Decide early.
- Pre-fabricated steel structures (e.g., press boxes). Goes to the modular sub, not the steel sub. Easy mis-allocation.
Mechanical, electrical, plumbing, fire protection
- The trench. Subsurface piping and conduit. Earth-worker assumes mechanical/electrical carries excavation and backfill; mechanical/electrical assumes earth-worker does. Mentioned in three separate interviews as the single most common interface gap.
- Generator field conditioning. The recurring multi-million-dollar gap. Some specs say mechanical does initial commissioning and electrical does top of; some say electrical does initial and owner does top of. Resolve per project.
- Motor starters. Chronic supply-responsibility war between electrical and mechanical. Sub will arrive at post-tender meeting and disclaim it. Name it in one scope.
- Heat tracing. Almost never on drawings. Experience-only. Add to your inferred scope library.
- Cast iron vs. PVC, copper vs. PEX. Subs substitute by market habit regardless of spec. Pin down per package or eat the credit at the close.
- Fire-rated louvres. Long lead. If the low bidder misses one, the GC may eat the schedule — $10,000/day in LDs against a $100 per-piece premium.
- Lighting control systems. Spec/drawing conflict is the norm: spec says “by owner,” drawing says “by electrical contractor.” RFI before bid.
- Owner-supplied gear and sole-source distributors (OFE/OFCI/CFOI). Read the spec for sole-source designations. Drawings may show install-only items as supply-and-install.
- BAS and low-voltage demarcation. Building automation, security, fire alarm subs all prefer to do their own low-voltage wiring. The scope matrix needs to say who pulls, who terminates, who commissions.
- Plumbing fixtures. Itemize by tag (T1/T2/T3 with basis-of-design manufacturer), not “toilets per spec.” Otherwise substitutions become disputes.
- Water-heated baseboards. Plumbing, electrical, and mechanical all duck this in residential. Assign explicitly.
- Painting of exposed conduit and electrical boxes. Lives in an electrical keynote; belongs to the painter. Move it before bid.
Drywall, framing, and interiors
- Wall blocking. Architectural shows blocking for cabinetry, TVs, toilet accessories, wood door frames; structural rarely details it. A perennial cross-trade scope gap.
- Insulation inside drywall scopes. Division 7 often missed under drywall packages. “The drywaller doesn't see insulation on it, he's not going to confirm that he has it or not, and that's a gap” (Pre-Con Manager, Canadian ICI GC).
- Hollow metal door frames. Drywaller often installs but the door sub also prices it. State “frames installed by drywall contractor; doors and hardware by Sub Z” in both scopes.
- Gypcrete naming collision. “Gypcrete” (poured underlayment) is a concrete-finisher scope, not drywall. Naming similarity is how this gets mis-allocated.
- Bulkhead/ceiling transitions. Acoustic tile to gypsum board junctures. Drywallers look at floor and ceiling plans, not special detail sheets. Cite the detail.
- Wood-frame vs. metal-stud assumptions. On a wood-frame multifamily, don't let a metal-stud coordination note from a previous job default into the drywaller package.
Thermal, moisture, and the building envelope
- Roof cover board. The most-cited high-dollar scope gap in our interviews. Always explicitly listed.
- Flashings at masonry-storefront transitions. Both subs exclude. Carry it yourself or assign explicitly.
- Snow, ice, and standing water removal from roof substrate. Roofer will exclude as “weather dependent.” Add explicitly.
- Ductwork insulation at the exterior envelope. Mechanical carries interior; the exterior-wall portion (e.g., 10 ft of rigid inside the wall box) is the orphan.
- Caulking. Exterior vs. interior is the perennial split. “You're responsible for caulking the exterior but not the interior” — name it; don't quote the spec, point to the detail.
- Fire-stopping. Choose: hire a single fire-stopping sub for all penetrations, or each trade does its own. Write the choice consistently across every trade scope so two subs don't both exclude.
Specialty equipment, finishes, and one-offs
- Elevators. State number of stops, travel distance, cab finishes, finish allowance, cab dimensions, type, basis-of-design manufacturer, and acceptable alternates. Anything less is a substitution trap.
- Curtainwall and exterior mock-ups. “It'll say please provide mock-up of this. Doesn't show on the drawings anywhere. That's a very expensive thing to build” (Senior Estimator, Canadian ICI GC).
- Lead-lined glass in medical imaging. $300K gap on a hospital we interviewed. Surface in the door and glazing scopes.
- Countertops. Tagged Division 12 by CSI; usually delivered by Division 6 millwork. Match scope to who actually builds it.
- Mass timber. Material protection on site is the canonical gap (the $10K glulam). “Include for protection of all materials delivered to site and while on site” must be in the scope.
- Mock-ups, RF-shielded rooms, atrium scaffolding. Frequency low, dollar impact high. Pull from spec and confirm with the sub at pre-bid.