Every Project Has a Budget - the Architect's Job Is to Keep the Design Within It at Every Phase
Construction cost estimating is a continuous activity throughout the design process, not a one-time calculation. The architect uses progressively more refined estimating methods at each phase of design, tracking the project's estimated cost against the owner's budget and flagging when design decisions are driving costs toward or over the budget ceiling. Failing to monitor cost through design - and discovering at bid opening that the project is 30% over budget - is one of the most damaging failures in the architect-client relationship. Understanding the estimating methods appropriate for each phase, their accuracy ranges, and how cost estimates are used to inform design decisions is tested on the ARE PjM exam as a project financial management skill.
Order of Magnitude (Rough Conceptual) Estimate
Used in pre-design and early programming, before any design has been done. Based on: historical cost per square foot for similar building types in the same market; published cost data (RSMeans Building Construction Cost Data, Building Construction Cost Index); and the architect's experience. Accuracy: +/- 25-35%. This estimate is sufficient to tell the owner whether their budget is in the right range for their program, but not to commit to any specific scope or quality. Common metrics: office building $250-450/SF; K-12 school $350-550/SF; hospital $700-1200/SF (all highly location-dependent).
Systems or Assemblies Estimate
Used at schematic design completion. Breaks the building into major systems (foundations, structure, exterior walls, roofing, mechanical, electrical, plumbing, interior finishes, site work) and estimates each system separately based on preliminary design decisions. More accurate than order of magnitude because it reflects actual decisions about structural type, MEP system type, and exterior envelope approach. Accuracy: +/- 15-20%. This estimate, combined with the owner's review and approval of the SD package, is the basis for the design development budget.
Unit Price (Quantity Takeoff) Estimate
Used at design development completion and at construction document completion. Itemizes all construction work in specific units (cubic yards of concrete, pounds of structural steel, square feet of exterior wall) and applies unit prices from cost data or subcontractor quotes to each quantity. Highly detailed - requires complete or near-complete drawings. Accuracy: +/- 5-10%. The quantity takeoff estimate at the end of construction documents should closely predict bid prices. Contractors use this method to prepare their bids.
Guaranteed Maximum Price (GMP)
In construction manager at-risk (CMR) project delivery, the construction manager commits to a Guaranteed Maximum Price - the maximum the owner will pay for the construction work. If actual costs exceed the GMP, the CM bears the overrun. GMP estimates are typically developed at 50-75% construction document completion, allowing the CM to coordinate with subcontractors for preliminary pricing. The GMP is a negotiated commitment, not just an estimate.
Key Exam Points
- Order of magnitude: pre-design; cost/SF from historical data; accuracy +/- 25-35%.
- Systems/assemblies estimate: SD completion; by major system; accuracy +/- 15-20%.
- Quantity takeoff/unit price: CD completion; line-item quantities × unit prices; accuracy +/- 5-10%.
- GMP: CM-at-risk only; cost commitment at 50-75% CD; CM bears overruns above GMP.
- Estimate progression: accuracy improves as design develops; architect monitors cost at each phase.
Study PjM on AREprep
AREprep’s PjM flashcards cover every concept on this exam with spaced repetition, and the practice exams mirror the real question formats so the actual test feels familiar.