A specification that names a product decides the outcome before the bids arrive. Sometimes that is intended. Frequently it is inherited from a previous project, and it excludes systems that would suit the site better.
This is written for the specifier, and its argument is not that our product should be named. It is that naming any product is usually the wrong move.
Why performance specification is better procurement
It is competitively neutral, which matters on public work where sole-sourcing invites challenge.
It lets the site decide. A specification written around riprap on a site with no local gradation, poor access, and no dewatering option produces either an expensive job or a substitution request.
It survives scrutiny. “Or equal” clauses attached to a named product generate arguments about what equal means. Criteria generate evidence.
It puts the burden on the bidder to demonstrate compliance, which is where it belongs.
What is genuinely specifiable
The honest list, because a performance specification full of unverifiable criteria is worse than a prescriptive one.
Straightforwardly specifiable
The design condition. Design event, design velocity or shear stress at the structure, water levels, wave condition where relevant. This is the requirement the armor has to meet.
Geometry. Plan extent, elevations, slope, thickness, toe treatment depth or apron dimension, crest elevation and freeboard, flank termination. These are design outputs and they belong in the specification whatever the system. See revetment anatomy.
The filter requirement. Specified against the bed material, which is site data you have.
Installation conditions. Whether placement must be achievable in flowing water, whether dewatering is permitted, the work window, and any access constraint. Naming these as requirements rather than assumptions is what lets a suitable system be offered.
Documentation. What must be submitted, which test methods results are required against, and what the manufacturer must publish about limitations.
Durability requirements expressed as the environment the material must survive: submerged, exposed, saline, abrasive, ice-affected, UV-exposed above water.
Maintenance expectation. Requiring bidders to state an inspection and maintenance regime makes the lifecycle comparison possible. See lifecycle cost vs. first cost.
Specifiable with care
Stability under the design condition. The right requirement, and the difficulty is the method of demonstration. Different systems have different accepted frameworks: riprap has established sizing methods, cast armor units have stability coefficients from physical model testing.
If you require demonstration by a specific method, you have effectively specified a family of products. If you require demonstration by “an accepted method,” you have to be willing to assess unlike evidence.
Being straight about our own position: we hold no citable physical model test results for wave stability, and on a design-wave-governed structure that is a real gap. When not to use rock bags says so. A specification requiring wave stability demonstrated by physical model testing is one we cannot meet, and that is a legitimate specification to write.
Not specifiable from us
Measured material property values. We publish which method backs which claim and which laboratory ran it, and we do not publish measured values. A specification requiring a minimum tensile value in stated units is one we cannot answer today.
That is a real constraint and a specifier should know it before writing the clause rather than after.
What to avoid
Naming a product without an equivalency route. Excludes everything else and invites challenge.
“Or approved equal” with no criteria. Moves the argument to after bid, where it is expensive.
Inheriting a specification from a different site. The commonest cause of a mismatched specification.
Specifying method where performance would do. “Placed on a prepared subgrade in the dry” is a method requirement that excludes every system placed in flowing water. If a dry working area is genuinely required, say why. If it is not, do not require it.
Requiring certifications that do not exist in this product category.
Silence on the filter, toe, and terminations. Those decide performance and a specification that omits them is incomplete regardless of what it says about the armor.
A workable structure
- Purpose and design condition — what the armor must resist
- Extent and geometry — plan, elevations, section, toe, crest, flanks
- Performance requirements — stability, durability in the stated environment, permeability, flexibility or conformance if the bed is mobile
- Interface requirements — filter, subgrade preparation permitted, transitions to adjacent treatment
- Installation constraints — wet or dry, window, access, plant limits, placement verification
- Submittals — product data, test methods and laboratories, published limitations, method statement, as-built
- Acceptance — how coverage and elevations are verified
- Maintenance — inspection regime the bidder must state
The one that changes the field most
Whether dewatering is required.
Nothing else in a specification excludes more options. If the section can be built wet, saying so opens the field substantially. If a dry working area is genuinely necessary for the permanent works, that is a legitimate requirement — but it should be a decision, not an inherited assumption. See what dewatering really adds.
Where to go next
- Getting a non-standard product approved
- How to compare unlike armor bids
- Revetment anatomy for the geometry to specify
- Assembling the submittal package
- When not to use rock bags
- The cost hub for the rest