Prescriptive, performance, and proprietary construction specifications

Before a submittal can be called compliant or deviating, you have to know what kind of spec it answers to. The same cut sheet can pass against a performance spec and fail against a proprietary one. A spec section is written using a few specifying methods, and the method in play decides how much room there is to pick a product and what proof the package needs.

The types at a glance

Type	What it pins down	Contractor's freedom	Path to a different product
Prescriptive (descriptive)	Material, dimensions, method	Low: match the description	Substitution request
Performance	The result to achieve	High: any product that meets it	None needed; prove the result
Proprietary, open	Named products, or equal	Named products or a proven equal	Or-equal submission
Proprietary, closed	A list of named products only	Pick from the list	Formal substitution request
Proprietary, sole-source	One named product	None	Formal substitution request, rarely granted
Reference standard	Compliance with a cited standard	Any product meeting the standard	Prove the standard

Prescriptive (descriptive) specifications

A prescriptive specification, which CSI calls descriptive, states exactly what to provide: the material, the dimensions, the construction, and often the installation method. It does not have to name a brand, but it describes the product so closely that only products matching that description qualify.

Gypsum board: ASTM C1396, Type X, 5/8 inch thick, tapered edges. Fasten to steel framing with 1-1/4 inch Type S screws at 12 inches on center on ceilings and 16 inches on center on walls.

How to recognize it: dimensions, gauges, thicknesses, materials, and methods stated as requirements. No manufacturer, no "shall achieve."

Why designers use it: the design depends on that exact construction, such as a rated assembly or a detail that has to match the drawings, and the designer wants certainty over contractor choice. The designer carries the risk that the described product works.

What to submit: product data that shows every described attribute, in the same units the spec uses. A value that does not match is a deviation even if your product is "just as good." The spec already decided what good means.

Performance specifications

A performance specification states the result the product has to achieve and leaves the means to the contractor. Any product that meets the stated performance is acceptable, whatever the brand.

Storefront system: design, engineer, and provide a system that withstands a design wind pressure of 30 psf with deflection not exceeding L/175, air infiltration not exceeding 0.06 cfm per square foot at 6.24 psf when tested per ASTM E283, and no water penetration at 12 psf when tested per ASTM E331.

How to recognize it: "shall achieve," "shall withstand," "minimum," "not to exceed," test methods with pass criteria, and often a requirement that the contractor's engineer design the system (delegated design).

Why designers use it: it opens competition and lets manufacturers bring their own engineering. It moves part of the design risk to the contractor, so the proof burden moves with it.

What to submit: proof of every number: test reports, calculations, and, where the spec delegates design, drawings and calculations sealed by a licensed engineer. AIA A201 (Section 3.12.10 in the 2017 edition) sets out how a contractor provides delegated design services when the contract documents call for them. The typical performance deviation is a gap in the numbers, a missing or insufficient value, rather than the wrong manufacturer. That is one of the six deviation categories a review sorts findings into.

Proprietary specifications

A proprietary specification names specific manufacturers and often specific products or model numbers. CSI's Construction Specifier breaks it into forms that differ in one question: can anything else be used?

Open proprietary names one or more products and allows equals:

Basis-of-Design Product: Armstrong Ultima 1912, or approved equal.

Closed proprietary lists acceptable products and nothing else:

Acceptable manufacturers: Hilti, 3M, or Specified Technologies Inc. No substitutions.

Sole-source names one product, no alternatives:

Door hardware cylinders: Best 1E series interchangeable core, to match the owner's existing keying system. No substitutions.

How to recognize it: manufacturer names, model numbers, "basis of design," "acceptable manufacturers," and the phrase that decides everything: "or equal," "or approved equal," or "no substitutions."

Why designers use it: to match existing equipment (keying systems, building automation, finishes), to lock in a product the rest of the design was sized around, or because the owner has a standard. The basis of design is usually written as an open-proprietary entry: one named product the design was built around, with equals allowed on proof.

What to submit: the named product, exactly, with its model number visible in the package. If you propose an equal under an open spec, submit it as an or-equal with a side-by-side comparison against the named product's salient characteristics. Under a closed or sole-source spec, anything else needs a substitution request approved before the product appears in a submittal. Our substitution request template lays out the comparison a reviewer expects.

Proprietary specs on public work

Public owners limit proprietary specifying because it restricts competition. California's Public Contract Code Section 3400 is a common example: an agency cannot call for a product by brand or trade name unless it is followed by "or equal." Unless the specs set another period, a bidder has 35 days after award to submit data supporting a substitution. The exceptions are narrow: a field test, matching products already in use on the public work, a product available from only one source, or an emergency. The agency has to make a finding for the exception and describe it in the bid documents. Federal agencies using brand-name-or-equal descriptions must state the salient physical, functional, or performance characteristics an equal has to meet (FAR 11.104), and specifying an item peculiar to one manufacturer requires justification (FAR 11.105). Some states discourage proprietary specifying on public work entirely. Check the bid documents and Division 01 for the rules on your project.

Reference-standard specifications

CSI's fourth method requires compliance with a published standard, such as an ASTM, ANSI, NFPA, or UL standard, without describing the product itself.

Concrete masonry units: ASTM C90, normal weight.

How to recognize it: "comply with," "conform to," or "in accordance with" followed by a standard number.

What to submit: proof the product meets the edition of the standard the spec cites, usually a test report or listing, not a data sheet line saying "meets ASTM." Most spec sections weave reference standards through their other methods, so a product can match a prescriptive description and still fail a cited standard. Both have to hold.

How to tell which type you are reading

Wording in the spec	Method	What it means for your submittal
Dimensions, materials, gauges, methods stated as requirements	Prescriptive	Match every attribute
"Shall achieve," "minimum," "not to exceed," test method with pass criteria	Performance	Prove every number
"Design, engineer, and provide" or "delegated design"	Performance with delegated design	Include sealed calculations and drawings
Brand or model "or equal" / "or approved equal"	Open proprietary	Named product, or an or-equal with proof
"Acceptable manufacturers" with "no substitutions"	Closed proprietary	Pick from the list
One named product, "no substitutions" or "to match existing"	Sole-source	That product only
"Comply with ASTM ..."	Reference standard	Show compliance with that standard

Most sections mix methods. A typical Part 2 names a basis-of-design product, adds performance requirements, and cites reference standards, so one product has to clear all three. Read the whole paragraph before deciding how much room you have. For where each method sits inside a section, see how to read a spec section.

Common mistakes

• Reading a prescriptive or proprietary spec as performance. "It performs the same" does not matter when the spec described or named an exact product. This is the root of most manufacturer substitution findings.
• Treating "or equal" as a blank check. The equal still has to match the named product's salient characteristics, and many specs require approval before the equal is submitted. See or-equal vs substitution request.
• Missing the reference standard. A product can match the description and still fail the ASTM or UL standard the same paragraph cites.
• Assuming performance means less paperwork. It usually means more. The rating has to be shown with a test report, not asserted on a brochure.
• Missing a delegated-design requirement. If the spec says the contractor designs the system, a package without sealed calculations is incomplete.

Before you send a package, run the pre-submittal checklist for your CSI division, or run a $35 check to see every deviation flagged against the actual spec language.

Frequently asked questions

What is a prescriptive specification in construction?

A prescriptive specification, also called descriptive, tells the contractor exactly what to provide: the materials, dimensions, construction, and installation method. It may not name a brand, but it describes the product closely enough that the contractor has to match the description rather than choose a product that performs the same.

What is an example of a prescriptive specification?

"Gypsum board: ASTM C1396, Type X, 5/8 inch thick, tapered edges. Fasten to steel framing with 1-1/4 inch Type S screws at 12 inches on center on ceilings and 16 inches on center on walls." It fixes the material, size, and fastening, and leaves nothing about the result to the contractor.

What is a proprietary specification in construction?

A proprietary specification names specific manufacturers and often specific products or model numbers. It is open when it allows or-equal products, closed when only the listed products are acceptable, and sole-source when it names one product with no alternatives.

What is the difference between closed proprietary and sole-source?

A closed proprietary spec can list several acceptable manufacturers, but nothing outside the list. A sole-source spec is the narrowest form: it names one manufacturer or product and nothing else is acceptable without a formal substitution the design team approves.

Are proprietary specifications allowed on public projects?

Often only with or-equal language or a documented reason. California's Public Contract Code Section 3400 bars public agencies from calling for a brand name unless it is followed by "or equal," with exceptions such as matching existing equipment, a field test, a product available from only one source, or an emergency. Federal agencies using brand-name-or-equal descriptions must list the salient characteristics an equal has to meet (FAR 11.104). Rules vary by state and owner, so check the bid documents.

What is the difference between a prescriptive and a performance specification?

A prescriptive spec defines the means: the exact product, material, or method. A performance spec defines the end: the rating, capacity, or result the product must achieve, and lets the contractor choose any product that meets it. Prescriptive puts the design risk on the designer; performance shifts more of it to the contractor.

How many types of construction specifications are there?

CSI describes four methods of specifying: descriptive, performance, reference standard, and proprietary. Many people use prescriptive as the umbrella for the methods that say what to provide, in contrast to performance. A single spec section usually mixes several methods.