What AACE classes are and why they matter
The American Association of Cost Engineers (AACE International) publishes Recommended Practice 18R-97, a five-class taxonomy for construction cost estimates based on design maturity and intended use. Every Vortex Estimating deliverable is graded against this scale so the recipient knows exactly how much precision to expect.
The taxonomy maps to two things: how complete the design is, and what the estimate will be used for.
The five classes
Class 5 — Concept Screening
Design maturity: 0-2% complete. Method: Analogous or parametric. Compare to past projects or use cost-per-SF databases. Accuracy: -50% to +100%. Use case: Feasibility, go/no-go decisions, screening multiple investment options. Real estate developer evaluating land acquisition. CEO pricing a hypothetical new facility for a board presentation. Typical turnaround: 24-48 hours.
Class 4 — Study or Feasibility
Design maturity: 1-15%. Schematic drawings, written program, gross areas defined. Method: Parametric with cost-per-unit-area or cost-per-capacity figures, plus major-equipment line items where industrial. Accuracy: -30% to +50%. Use case: Project authorization. Business case for capital request. Owner setting initial budget for design team to work toward. Typical turnaround: 3-5 business days.
Class 3 — Budget, Authorization, Control
Design maturity: 10-40%. Design development complete, equipment lists firming up, structural system selected. Method: Semi-detailed unit-cost estimates against measured assemblies. Major bulk quantities taken off, smaller items estimated parametrically. Accuracy: -20% to +30%. Use case: Budget setting, capital cost approval, design-control budget. Most owner-side budgets used during the design process land here. Typical turnaround: 5-10 business days.
Class 2 — Control or Bid/Tender
Design maturity: 30-70%. Construction documents largely complete. Method: Forced-detail unit-rate estimate. Full quantity takeoff against the working drawings. Accuracy: -15% to +20%. Use case: Cost control during construction, fixed-budget validation, design-build target pricing, GMP negotiation. Typical turnaround: 7-12 business days for typical commercial.
Class 1 — Bid or Tender
Design maturity: 65-100%. Construction documents complete and issued for bid. Method: Full bottom-up. Every quantity counted, every labor productivity reviewed. Accuracy: -10% to +15%. Use case: Hard-bid submission, GMP negotiation, claim defense, contract dispute resolution. Typical turnaround: 10-20 business days for full commercial projects; faster for narrow scope.
How to pick the right class
Three questions to ask:
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What stage is the design? If you have only a written program, you’re at Class 5 or 4. If you have schematic drawings, Class 4. Design development, Class 3. Substantially complete CDs, Class 2 or 1.
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What are you using it for? Feasibility = Class 5 or 4. Budget authorization = Class 3. Hard bid = Class 1. Control during construction = Class 2.
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What’s your tolerance for being wrong? A Class 5 budget being 100% high is fine for feasibility (you don’t pursue the project) but catastrophic for a hard bid (you lose to a competitor at the real price). Match the class to the consequence of being wrong.
Contingency by class
Each class carries a different contingency percentage to reflect the unknowns at that design stage:
| Class | Typical Contingency |
|---|---|
| 5 | 30-50% |
| 4 | 20-30% |
| 3 | 15-20% |
| 2 | 10-15% |
| 1 | 5-10% |
The contingency is what’s reserved for “unknowns we haven’t identified yet.” More design = fewer unknowns = less contingency.
The wrong class is worse than no estimate
A Class 5 estimate presented as a Class 1 bid is malpractice. So is a Class 1 estimate produced from schematic drawings — there isn’t enough information to support that precision.
When we engage with you, we tell you up-front which class the estimate will be based on the documents you provide. If you need Class 1 precision but only have Class 4 design maturity, we tell you that too — and we recommend you wait for more design before going to hard bid.
What this looks like in practice
A typical real-world progression on a $40M commercial project:
| Stage | Drawings % | AACE Class | Use |
|---|---|---|---|
| Feasibility | 0% | Class 5 | Pro-forma, land decision |
| Schematic Design | 15% | Class 4 | Budget authorization |
| Design Development | 35% | Class 3 | Owner budget approval |
| 60% CDs | 60% | Class 2 | Design-control check |
| Issued for Bid (100%) | 100% | Class 1 | Hard bid |
Same project, five different estimates, each at the right class for what it’ll be used for.
If you want to see how this plays out on your project, send us your drawings and we’ll tell you what class makes sense for what you need.