Basis of Design, Proprietary and Performance Specifications

Why this matters

Before a shop decides what to buy for a commercial job, it has to know how much freedom the spec actually gave it, and how much responsibility comes attached to that freedom. Specifiers name products in four different ways, and each one moves a different line. One lets you change nothing. One lets you change the product but makes every knock-on change yours. One lets you buy anything that meets a standard but makes you prove it. One lets you design the thing yourself and holds you to the result. Reading all four as "the spec says this, or equal" is how a shop ends up owning a heavier unit on a roof nobody checked.

The four methods side by side

Most real sections mix these: a performance requirement for the equipment, a basis of design to show the size and shape the designer had in mind, and reference standards for materials. Read each paragraph for which method it is using.

Proprietary: one product, and why a specifier does it

A closed proprietary spec names one product with no substitutions. Owners use it to match equipment they already run, to stay inside a fleet they service with their own staff, to keep a controls system on one platform, or because a warranty depends on it. An open proprietary spec names one or more products and allows others through a substitution procedure.

What it gives the contractor is certainty: no selection risk, no design argument. What it takes away is the price lever. If the named product is unavailable or has a lead time that breaks the schedule, the move is a written substitution request under the procedures in Division 01, not a quiet swap (see related: How to Write a Substitution Request the Engineer Can Approve).

Basis of design: the named product is a benchmark

Under a basis of design (some say "base of design"), the named product is the one the designer used to draw the job. Its dimensions set the space, its weight went into the structural check, its electrical data set the feeder on the electrical sheets, its connections set the piping and duct layout. Listed alternates are allowed, but "subject to compliance" means the alternate must meet every requirement in the section, and the section commonly adds that any change the alternate forces on other work is at the contractor's cost, including redesign by the engineers.

That second clause is where the money is. A listed equal is not pre-approved to fit; it is pre-approved to be considered. Whether "or equal" language lets you go further, to an unlisted product the shop believes is equivalent, is its own argument (see related: Specification Compliance and the Or Equal Question).

Reference standard: anything that meets the number

A reference standard spec names a published standard instead of a product. "PVC pipe: ASTM D1785, Schedule 40" admits every manufacturer whose pipe meets D1785 at that schedule. "Copper tube: ASTM B88, Type L" admits any Type L tube, and rules out Type M, which B88 also covers and which has a thinner wall. A crew that grabs Type M off the truck because it is copper and the right size has installed a nonconforming product, and the marking on the tube proves it.

The contractor's burden is compliance and proof: product markings, listings, mill certificates or test reports, whatever the section asks for. The standard also carries its own edition and limits. Read what the standard covers before assuming it covers your use; a standard for the pipe is not a standard for the fittings or the joining method.

Performance: you choose the means and own the result

A performance spec describes what the finished work must do and leaves the how to the contractor. "Provide seismic restraint for suspended equipment designed for the forces required by the building code" is typical. So is "the heating system shall maintain the scheduled space temperatures at the scheduled outdoor design condition."

Two consequences follow. First, the result is the acceptance test, so the section will say how it is measured, and a system that does not meet it is not complete however good the parts. Second, performance language often comes with delegated design: the section requires the contractor to engage a licensed design professional to design the component, and to submit sealed calculations and drawings. A shop that bids performance work without pricing an engineer, or without one available, has bid a design it cannot legally produce where the state licenses that design work. Who is liable when a delegated design fails, and how that liability splits with the engineer of record, is a question for the shop's own attorney and its insurance agent.

Worked example: a listed equal on a rooftop unit

A renovation specifies a new rooftop unit as a basis of design, with two other manufacturers listed as acceptable subject to compliance. The section carries the common clause: costs of changes to other work caused by a product other than the basis of design are the contractor's. The HVAC shop's supplier offers a listed equal with a shorter lead time and a better price. The estimator compares submittal data, not brochures. The figures below are illustrative but typical in shape:

Weight. The equal is 1,380 minus 1,150, which is 230 lb heavier, and 230 divided by 1,150 is 20 percent. The structural engineer checked the roof for 1,150 lb. A 20 percent increase on an existing roof is not something the shop decides; it goes to the engineer through the submittal, and the review is at the shop's cost under the clause.

Curb. The equal's footprint does not match the existing curb, so an adapter curb is needed, and the roofer has to flash it. That is material, labor and a second trade's time, all carried by the shop.

Electrical. The electrical sheets show the basis-of-design feeder: 8 AWG copper on a 50 A breaker. NEC Table 310.16, as adopted by your jurisdiction, rates 8 AWG copper at 50 A in the 75 C column that typical terminations allow. That covers the basis of design's 38 A MCA. It does not cover the equal's 52 A MCA. The next size, 6 AWG copper, is rated 65 A in the same 75 C column, which clears 52 A. The breaker is then normally chosen at or above the 52 A MCA and must not exceed the 70 A MOP on the equal's nameplate, so the 50 A breaker goes too. Pulling a new feeder from the panel to the roof is the electrician's work, priced by the electrician, and under the clause it lands on the HVAC shop's ticket.

The decision. The equal's lower unit price and shorter lead time have to pay for a structural review, an adapter curb with flashing, and a replacement feeder and breaker before they save anything. On this job they did not: the shop submitted the basis of design and used the lead-time difference to schedule the crane day earlier. On a new building where the roof, curb and feeder had not yet been built, the same equal might have cost nothing extra, because the designers could have drawn to it from the start. That is the condition that flips this answer: whether the work the alternate disturbs already exists.

The failure mode. A shop that reads "listed equal" as "pre-approved" orders the cheaper unit, sets it on the old curb with shims, and has the electrician land it on the existing 8 AWG feeder. The submittal reviewer may not catch it, because a reviewer checks general conformance and does not take over the contractor's coordination (see related: What a Submittal Review Stamp Means and What It Does Not). The inspector or the first hot afternoon does.

If the shop does submit the equal. The submittal's cover letter lists every difference from the basis of design, in the same terms as the table above: weight and the percentage, curb fit, MCA and MOP against the feeder shown on the electrical sheets, and the work each difference triggers. A difference the reviewer was told about in writing can be accepted or rejected on purpose. A difference buried in a data sheet is still the shop's when it surfaces on the roof.

How to read any product paragraph in thirty seconds

Ask three questions in order. Does it name one product, several, a standard, or a result? Does it say "no substitutions," "subject to compliance," or "or equal"? And is there a sentence, here or in Division 01, that says who pays for the consequences of choosing something other than the first name on the list? The answers tell you what you may buy and what you are signing up for when you buy it.

References

• ASTM B88 (seamless copper water tube) and ASTM D1785 (PVC pipe, Schedules 40, 80 and 120), in the editions the specification names.
• NFPA 70 (NEC), as adopted by your jurisdiction: Table 310.16 conductor ampacity; Article 440 for air-conditioning equipment nameplate MCA and MOP.
• See related: Specification Compliance and the Or Equal Question
• See related: The Three-Part Spec Section: General, Products, Execution; The MasterFormat Divisions a Service Trade Lives In
• See related: How to Write a Substitution Request the Engineer Can Approve