Construction specification types: prescriptive, performance, and proprietary
The three types of construction specifications, when each is used, substitution clauses, and how spec type affects drawing coordination and submittals.
Why this matters
Specification type drives how contractors price, what they can substitute, and how you enforce quality. Prescriptive specs name specific brands; performance specs define required outcomes but allow flexibility. Proprietary specs (only Brand X) limit competition but ensure exact performance. Mixing them creates disputes: contractors claim they can substitute; owners claim the spec is fixed. Understanding spec type prevents conflicts and clarifies submittal expectations.
The Three Specification Types
Prescriptive
Names specific product brands/models, or equivalent. Tells contractor exactly what to use.
Performance
Specifies required performance (R-value, fire rating, load capacity). Product choice up to contractor.
Proprietary
Only one brand/product specified; no substitutions allowed or listed. Most restrictive.
Prescriptive Specifications
Definition
Specifies exact product(s) by brand and model. Example: "Insulation: Owens Corning Fiberglas board, 3" thick, R-12 minimum"
Pros
- Clear & enforceable; no ambiguity
- Contractor knows exact cost upfront
- Quality is known (specified product is proven)
- Easy to inspect (check if installed product matches spec)
Cons
- Limits competition; may increase cost
- If product becomes unavailable, spec violation occurs
- "Or equal" clauses create disputes
- Requires detailed product knowledge upfront
Example
"Roofing: GAF Timberline HD shingles, weathered gray, impact-resistant (IR) rated, or pre-approved equal"
"Or Equal" clause problem
If spec says "Brand X or equal," disputes arise: What makes something "equal"? Must the contractor get approval? Can they substitute without asking? Always clarify the substitution process upfront.
Performance Specifications
Definition
Specifies the required outcome/performance, not the product. Contractor chooses how to meet it. Example: "Insulation: Minimum R-12 thermal resistance per ASTM C518"
Pros
- Contractor can choose cost-effective product
- Promotes competition; often lowers price
- Flexibility if preferred product becomes unavailable
- Focuses on what matters: end performance, not brand
Cons
- Requires contractor to research and propose options
- Verification (testing) may be needed to confirm performance
- Disputes over whether chosen product meets spec
- Submittal process more complex
Example
"Concrete: Minimum 4000 psi compressive strength (28-day), 0.55 w/c ratio, tested per ASTM C39"
Testing & verification
Performance specs require proof that the chosen product meets spec. Expect submittals with test reports, certificates of compliance, and sometimes field testing (e.g., concrete samples, insulation R-value tests).
Proprietary Specifications
Definition
Only one specific product (brand & model) allowed; no substitutions. Example: "HVAC: Trane Sintesis air-cooled chiller, Model RTAA-200, no substitutions allowed"
Pros
- Zero ambiguity; exact product required
- Ensures compatibility with system design (one manufacturer)
- Streamlined submittal process (only one option to approve)
- Simplifies warranty/service if all equipment is one brand
Cons
- No competition; highest cost likely
- If product discontinued, spec violation
- Contractor has no flexibility
- May require AIA Form A-133 (single-source justification)
When Used
Integrated systems that require one manufacturer (e.g., curtain wall systems, integrated building management, BIM-modeled structural systems). Sometimes used when one product is clearly superior and justifies the cost.
How Spec Type Affects Coordination
Prescriptive Specs
Easier to coordinate. Drawings reference the specified product by name/model. MEP plans can reference "Carrier 50JH chiller" and structural knows exact equipment dimensions.
Performance Specs
Harder to coordinate. Drawings cannot reference a specific product (contractor hasn't chosen yet). Structural must show "Equipment room for chiller, dimensions TBD per submittal." Requires contingency space in design.
Proprietary Specs
Tightest coordination. All trades design around the one specified product. No flexibility. Risk: if that product becomes unavailable, design must change.
Substitutions & the Submittal Process
How Spec Type Affects Submittals
Prescriptive
Submit product info for specified brand
If substitution: submit "equal" product with detailed comparison
Owner approval required (may be denied)
If substitution: submit "equal" product with detailed comparison
Owner approval required (may be denied)
Performance
Submit multiple product options
Include test data proving performance
Owner selects option or accepts contractor's choice
Include test data proving performance
Owner selects option or accepts contractor's choice
Proprietary
Submit specified product only
No substitutions allowed
Quick approval (one option)
No substitutions allowed
Quick approval (one option)
Substitution strategy
If your spec says "Brand X or equal," always require contractor to submit the "equal" product for approval BEFORE ordering. Document approval in writing. This prevents disputes: contractor can't claim their choice was approved when it wasn't.
Mixing Specification Types (Avoid This)
Many projects mix all three types. This creates confusion and disputes:
Example Conflict
Section 08-11 (doors): Prescriptive, "Jeld-Wen 3000 Series" (exact brand)
Section 03-30 (concrete): Performance, "4000 psi, any brand acceptable"
Section 13-01 (specialties): Proprietary, "Only Horton doors; no substitutes"
Result: Confusion. Some trades can substitute; others can't. Submittal process varies.
Best Practice
Pick one spec type and stick with it across the project. If mixing is unavoidable, clearly label each section: [PRESCRIPTIVE], [PERFORMANCE], [PROPRIETARY]. Define substitution process upfront. This prevents contractor confusion and RFI disputes.
Which Type to Use When
Use Prescriptive When
- You know exactly what product you want (proven track record)
- Quality/aesthetics matter more than cost
- Designs rely on specific equipment dimensions
- Project is small and tight on schedule (fewer submittals)
- You need tight quality control
Use Performance When
- You want to encourage competitive bidding (lower cost)
- Multiple products meet your needs equally well
- You want contractor innovation/optimization
- Product choices can vary without affecting design (e.g., insulation R-value)
- You can accept testing/verification costs
Use Proprietary When
- Product is unique/patented (no equal exists)
- Integrated system requires single manufacturer (curtain walls, BMS)
- Warranty or service requires single source
- Quality/reliability justifies premium cost
- Design depends critically on exact product (no flexibility)
Choose your specification approach based on project goals: prescriptive for control, performance for cost, proprietary for integration. Clear specs reduce disputes, RFIs, and change orders. Ambiguous specs ("or equal" without definition) breed conflicts. Be explicit about what you require and how substitutions will be approved.
Keep exploring
Related references for specifications, substitutions, and submittals.