17.7 Quantity Takeoff Estimating, General Conditions, Overhead & Alternates

Complementary Documents, Conflict Resolution & Precedence

During bidding and construction, discrepancies inevitably arise between graphic representations on the drawings and written requirements in the Project Manual.

The Doctrine of Complementary Documents (AIA Document A201)

A central canon of standard American construction contracts is codified in AIA Document A201 Section 1.2.1:

"The Contract Documents are complementary, and what is required by one shall be as binding as if required by all; performance by the Contractor shall be required only to the extent consistent with the Contract Documents and reasonably inferable from them as being necessary to produce the indicated results."

Under this complementary doctrine, the Contract Documents are legally designed to be interpreted as an integrated whole. The architect is not legally obligated to duplicate every item on both the drawings and specifications. If an item is depicted on the drawings (e.g., an acoustical tile ceiling shown in a reflected ceiling plan) but inadvertently omitted from the finish schedule or specifications, or vice versa, the contractor is contractually bound to provide that item without an increase in the contract sum or contract time.

Order of Precedence: AIA Standard vs. Customized Contracts

• AIA Philosophy (No Precedence Clause): Standard AIA contract documents (such as AIA A101 and A201) intentionally omit an Order of Precedence clause. The AIA asserts that establishing an artificial legal hierarchy (such as declaring that specifications always supersede drawings) encourages careless document coordination and can allow an outdated, generic boilerplate specification clause to override a carefully resolved, site-specific architectural detail. Instead, A201 obligates the contractor to examine the documents carefully and promptly submit a Request for Information (RFI) to the architect upon discovering an error, inconsistency, or omission (Section 3.2.2). The architect then issues an official written interpretation or clarification (Section 4.2.11).
• Judicial Common-Law Rules of Interpretation: When an irreconcilable conflict between documents ends up in litigation or arbitration without an explicit contractual precedence clause, courts apply established common-law rules of contract interpretation:
  1. Specifications Govern Quality; Drawings Govern Quantity: Written specifications determine materials, quality standards, finishes, and workmanship; drawings determine quantities, geometric dimensions, physical locations, and spatial relationships.
  2. Specific Governs General: A large-scale detailed drawing (e.g., a 1-1/2" = 1'-0" wall section detail) governs over a small-scale general plan (e.g., a 1/8" = 1'-0" overall floor plan).
  3. Written Words Govern Figures: Explicit spelled-out text notes govern over graphic symbols; figured numerical dimensions govern over dimensions scaled directly with a ruler.
  4. Chronological Hierarchy: Addenda issued during bidding supersede original drawings and specifications; fully executed Change Orders signed by the Owner, Architect, and Contractor supersede all prior contract documents.
• Customized Owner Precedence Clauses: Private corporate and public institutional clients frequently amend standard agreements to insert a rigid legal Order of Precedence Clause. A typical hierarchy reads: (1) Signed Change Orders, (2) Signed Owner-Contractor Agreement, (3) Addenda, (4) Supplementary Conditions, (5) General Conditions (A201), (6) Division 01 General Requirements, (7) Technical Specifications (Divisions 02–49), (8) Large-Scale Detail Drawings, (9) Small-Scale Drawings. Architects must strictly align their documentation practices with any precedence clause contained in the owner's customized agreement.

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Contractor Quantity Takeoff Estimating & Cost Structure

To prepare a competitive, profitable lump-sum or Guaranteed Maximum Price (GMP) bid, general contractors and commercial cost estimators perform a comprehensive Quantity Takeoff (QTO). The quantity takeoff converts two-dimensional architectural drawings and three-dimensional BIM models into an exhaustive bill of materials and discrete labor activities.

ANATOMY OF A CONTRACTOR LUMP-SUM BID
┌─────────────────────────────────────────────────────────────────────────────┐
│ DIRECT CONSTRUCTION COSTS (Hard Costs)                                      │
│ • Net Material Takeoff Quantities + Material Waste Factors (5% to 10%)      │
│ • Direct Trade Labor (Hourly Wage + Burden + Productivity Rates)            │
│ • Trade Subcontractor Lump-Sum Bids (Mechanical, Electrical, Concrete)      │
│ • Construction Equipment Rental (Scissor lifts, backhoes, concrete pumps)   │
├─────────────────────────────────────────────────────────────────────────────┤
│ GENERAL CONDITIONS COSTS (Division 01 Jobsite Field Overhead: 6% to 12%)    │
│ • On-site Project Superintendent, Project Manager, Field Engineer salaries  │
│ • Jobsite Field Office Trailer, computers, printers, internet               │
│ • Temporary Utilities (Electric power, water, winter heating, lighting)     │
│ • Site Security, perimeter fencing, barricades, signage                     │
│ • Waste Management (Dumpsters, debris hauling, recycling mandates)          │
│ • Scaffolding, staging, hoists, cranes, safety equipment                    │
│ • Building permits, plan check fees, testing and inspection services        │
├─────────────────────────────────────────────────────────────────────────────┤
│ CONTRACTOR OVERHEAD & PROFIT (OH&P: 8% to 15% combined)                     │
│ • Home Office Overhead (Corporate office rent, executive salaries, legal)   │
│ • Contractor Net Profit Margin (Risk reward, return on capital)             │
├─────────────────────────────────────────────────────────────────────────────┤
│ CONTINGENCY & BONDS                                                         │
│ • Contractor Estimating Contingency (design refinement allowance)           │
│ • Performance and Payment Bonds (typically 1% to 2% of total contract)      │
└─────────────────────────────────────────────────────────────────────────────┘

Net Takeoffs vs. Material Waste Factors

Estimators measure net physical dimensions directly from the drawings using specialized takeoff software (e.g., Bluebeam Revu, On-Screen Takeoff) or direct BIM model quantification:

• Cubic Yards (CY): Concrete foundations, footings, structural slabs, mass excavation, and backfill. (Calculated as $\text{Length [ft]} \times \text{Width [ft]} \times \text{Thickness [ft]} / 27$).
• Square Feet (SF) or Squares: Drywall partitions, acoustic ceilings, ceramic tile, resilient flooring, wall sheathing, building wraps, exterior insulation, paint, and roofing membranes. (One roofing "square" = $100\text{ sq ft}$).
• Linear Feet (LF): Cold-formed steel studs, wood framing plates, interior baseboards, millwork moldings, plumbing piping, electrical conduits, and perimeter flashing.
• Piece / Unit Count (Each): Doors, frames, locksets, luminaires, plumbing fixtures, roof drains, and kitchen equipment.
• Weight in Tons / Hundredweight (cwt): Structural steel wide-flange beams and columns (calculated by multiplying member linear footage by its nominal pound-per-foot weight; e.g., $100\text{ LF}$ of W14x90 steel weighs $9,000\text{ lbs}$, or $4.5\text{ tons}$).

Mandatory Waste Factors: Estimators never purchase raw net takeoff quantities. Unavoidable geometric cutting losses, edge trimmings, drop-off scrap, transport breakage, and material lap joints require adding realistic waste allowances:

• Gypsum Board: $5%$ to $10%$ waste (elevated to $12%$ to $15%$ in spaces with complex curved soffits, angular walls, or high reveals).
• Ceramic / Porcelain Tile: $10%$ to $15%$ waste (required for perimeter cut tiles, grout alignment, pattern matching, and owner-mandated attic stock).
• Cast-in-Place Concrete: $5%$ to $8%$ waste (accounting for trench over-excavation, formwork deflection, and spillage).
• Framing Lumber & Studs: $10%$ to $15%$ waste.

General Conditions Costs (Division 01 Field Overhead)

General Conditions costs encompass the indirect, operational expenses incurred on the physical jobsite that cannot be allocated to a single trade or material. These costs represent the logistical infrastructure required to execute the work specified in Division 01. On typical commercial projects, General Conditions represent $6%$ to $12%$ of the direct construction cost.

Contractor Overhead and Profit (OH&P)

To the sum of direct trade costs and General Conditions costs, the contractor applies markups for overhead and profit:

• Home Office Overhead (Indirect Overhead): Recoups corporate operating costs incurred off-site, including corporate headquarters rent, executive and accounting salaries, marketing, legal counsel, and general corporate liability insurance; typically $2%$ to $5%$.
• Contractor Profit: The net financial return earned by the contractor for assuming construction risk, managing capital, and delivering the project; typically $3%$ to $6%$.
• Combined OH&P: In commercial construction bidding, combined OH&P typically ranges from $8%$ to $15%$, fluctuating based on local economic competition, project complexity, and delivery method.

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Bid Alternates and Unit Prices

To safeguard the owner's budget against market volatility on bid day, architects utilize Bid Alternates and Unit Prices structured within Division 01 (Section 01 20 00 Price and Payment Procedures).

Add Alternates vs. Deduct Alternates

An Alternate is a clearly defined, modular package of work for which the bidder submits a separate, discrete price addition or deduction from the base bid:

• Add Alternate: Specifies an additive item of work that the owner may choose to incorporate into the contract if the base bid comes in below the owner's budget (e.g., "Add Alternate 1: Provide high-performance standing-seam zinc roofing in lieu of standard SBS-modified bitumen roofing").
• Deduct Alternate: Specifies a scope reduction or material downgrade that the owner may select if base bids exceed the budget (e.g., "Deduct Alternate 1: Delete finished acoustical wood ceiling panels in the auditorium and provide standard painted drywall").
• Professional Standard of Care: Architects should strongly prefer Add Alternates over Deduct Alternates. When contractors price deduct alternates during competitive bidding, they frequently offer disproportionately small financial credits—often withholding the labor savings, general conditions, and profit margin originally baked into that work. Conversely, add alternates foster fierce competitive pricing among bidders eager to win the contract, resulting in fair market valuations for the added scope.

Unit Prices

A Unit Price is a predetermined fixed price per unit of measurement (e.g., per cubic yard of mass rock excavation, per linear foot of helical micro-pile, per square foot of concrete slab scarification) established in the bid documents:

• Unit prices are utilized when the exact physical quantity of a required item of work cannot be reliably determined prior to field construction (most commonly in subsurface foundation conditions, utility relocations, or structural concrete restoration).
• The contractor's quoted unit price includes all necessary material, labor, equipment, waste, general conditions, overhead, and profit for that specific unit.
• If the geotechnical engineer encounters $150\text{ CY}$ of unexpected subterranean bedrock during basement excavation, the contractor is reimbursed based on the predetermined unit price (e.g., $150\text{ CY} \times $180/\text{CY} = $27,000$), completely avoiding contentious change order disputes and schedule delays.