14.7 Cost Estimating by Phase & Contingency Planning

Cost Estimating Hierarchies Across Design Phases

Financial stewardship is a core professional responsibility of the licensed architect. Under standard contract frameworks (such as AIA Document B101-2017, Section 6.2), the architect must evaluate the owner's budget for the Cost of the Work and provide preliminary cost evaluations at each design milestone. If the lowest bona fide contractor bid or negotiated proposal exceeds the agreed budget, the architect may be contractually obligated under B101 Section 6.7 to redesign the project at zero additional fee. On the ARE 5.0 Project Planning & Design (PPD) division, candidates must navigate the progressive hierarchy of cost estimating methodologies, understand contingency burn-down rates, and perform life-cycle cost economic analyses.

                         PROGRESSION OF COST ESTIMATING TIERS

   Schematic Design (SD)         Design Development (DD)        Construction Documents (CD)
  ┌─────────────────────────┐   ┌─────────────────────────┐   ┌───────────────────────────┐
  │   Square-Foot / Area    │   │   Systems / Parameter   │   │  Unit Price / MasterFormat│
  │  Historical Cost Data   │──►│   Assembly Unit Costs   │──►│  Granular Quantity Takeoff│
  │  Accuracy: ±15% to ±20% │   │   Accuracy: ±10%        │   │  Accuracy: ±5%            │
  └─────────────────────────┘   └─────────────────────────┘   └───────────────────────────┘

1. Square-Foot & Area Estimating (Schematic Design)

During pre-design and Schematic Design (SD), the architectural project exists primarily as spatial program diagrams, gross floor areas, and preliminary massing models. Specific wall assemblies, structural grids, and mechanical chillers have not yet been selected.

• Methodology: The architect utilizes historical construction cost reference databases (such as RSMeans Building Construction Cost Data). A baseline cost per gross square foot (GSF) is selected based on building occupancy typology (e.g., $320/sq ft for an elementary school; $480/sq ft for an outpatient surgical clinic) and multiplied by total Gross Floor Area.
• Modifying Factors & Regional Adjustments:
  • City Cost Index (CCI): Construction costs vary drastically by geographical region due to local labor wages, union vs. non-union market penetration, material freight logistics, and local building codes. RSMeans publishes quarterly City Cost Indexes benchmarked against a national 30-city average (100.0). For example, if the national base cost of a high school is $300/sq ft, and the local CCI for New York City is 135.2, the localized base cost is $300 \times 1.352 = $405.60/sq ft. If building in rural Arkansas with a CCI of 78.5, the adjusted cost is $300 \times 0.785 = $235.50/sq ft.
  • Inflation & Cost Escalation: Construction cost estimates represent costs on the day the estimate is drafted. Because major commercial projects require 12 to 24 months of design and bidding before groundbreaking, future construction inflation must be compounded to the projected midpoint of construction: $\text{Escalated Cost} = \text{Base Cost} \times (1 + r)^t$ Where $r$ is the annual construction inflation rate and $t$ is the elapsed time in years from estimate date to construction midpoint.
  • Perimeter / Shape Factor: The ratio of exterior envelope skin area to gross floor area significantly impacts unit costs. A compact 50,000 GSF square building (224 ft x 224 ft) has an exterior perimeter of 896 linear feet. A highly articulated or fragmented 50,000 GSF building (courtyards, finger wings) with an exterior perimeter of 1,600 linear feet requires 78% more exterior wall cladding, foundation footing, parapet coping, and insulation per square foot of interior floor space, driving up overall square-foot costs by 15% to 25%.
  • Story Height Factor: Baselines assume standard floor-to-floor heights (typically 12 feet for commercial office). Buildings requiring 16- to 18-foot floor-to-floor heights (performing arts, laboratories, athletic facilities) require vertical scaling adjustments to account for longer structural columns, taller partition framing, taller risers, and expanded exterior facade square footage.

2. Systems / Parameter Estimating (Design Development)

During Design Development (DD), the design team locks in major building assemblies: structural steel composite deck vs. concrete flat plate; masonry cavity wall vs. glazed aluminum curtain wall; central VAV vs. VRF.

• Methodology: Parameter estimating evaluates costs per unit of system assembly rather than overall building floor area. This technique bridges macro-level square-foot estimates and granular takeoffs:
  • Exterior Skin: Cost per square foot of gross exterior envelope area, segmented into vision curtain wall ($120/sq ft), opaque rainscreen ($65/sq ft), and punched windows ($85/sq ft).
  • Interior Partitions: Cost per linear foot of partition (differentiated by 1-hour drywall, 2-hour demising walls, CMU).
  • Structural Framing: Cost per pound or ton of structural steel framing, or cost per cubic yard of placed concrete.
  • HVAC & Mechanical: Cost per ton of cooling capacity (e.g., $3,500/ton for central chilled water plant) or cost per CFM of conditioned air distributed.
  • Plumbing: Cost per fixture count or Drainage Fixture Unit (DFU).
  • Electrical Distribution: Cost per connected kVA or watts per square foot.
• Architectural Trade-Off Analysis: Parameter estimating enables rapid, rigorous cost-benefit trade-offs. If the owner wants to upgrade an exterior skin from metal composite panels to custom terra cotta baguette rainscreens, parameter pricing immediately isolate the net cost impact on the facade subsystem without re-estimating the entire building.

3. Unit Price / Quantity Takeoff Estimating (Construction Documents)

During Construction Documents (CD) and contractor bidding, drawings and specifications are 100% complete.

• Methodology: The estimator performs a granular measurement (Quantity Takeoff) of every physical component in the project, organized strictly by the CSI MasterFormat 50-Division System:
  • Division 03 30 00 (Cast-in-Place Concrete): Exact cubic yards of footing concrete, tons of grade 60 rebar, square feet of plywood formwork.
  • Division 09 22 00 (Support for Plaster and Gypsum Board): Linear feet of 20-gauge 3-5/8-inch metal studs, square feet of 5/8-inch Type X gypsum board, pounds of drywall screws, rolls of joint tape, gallons of joint compound.
• Direct vs. Indirect Costs:
  • Direct Costs (Bare Costs): The physical expenditures directly incorporated into the permanent structure: material purchase prices, equipment rental rates (cranes, excavators, lifts), and skilled labor craft hours.
  • Indirect Costs (General Conditions / Overhead & Profit): Expenditures necessary to manage construction that do not become part of the physical building: project superintendent and project manager salaries, temporary job trailer rental, temporary electrical service and winter heating, temporary perimeter safety fencing, site security, dumpster waste hauling, scaffolding, municipal building permit fees, builder's risk insurance, performance and payment bonds, corporate home office overhead, and general contractor profit margin. General conditions and O&P typically add 15% to 25% on top of bare direct costs.