Let’s understand these definitions first. Archtoolbox.com has some really good explanations of types of construction specifications:
“Prescriptive specifications convey the requirements of a project through a detailed explanation of the materials that the contractor must use and the means of installing those materials.”
“Proprietary specifications are those that require the use of a single approved product type for any particular installation.”
“A performance specification is a document that specifies the operational requirements of a component or installation. Simply put, a performance specification tells the contractor what the final installed product must be capable of doing. The contractor is not instructed as to how to accomplish the task of meeting the performance specification requirements - only as to how the component must function after installation.”
In practice, many specifications are hybrids, which name products and list performance criteria. There are pros and cons to each approach.
The primary reason is that green roofs are most often installed as stormwater management devices. Stormwater management devices must perform. After selecting a green roof system and designing the green roof for optimal performance, the next most important action item is documenting performance requirements in specifications. Performance requirements might include retaining a certain volume of water, or being within a certain weight range, or lowering peak flow by a certain percentage during certain storm events.
“But the nice sales rep who visited my office told me their green roof meets all our needs, and I just need to put their name in the spec.”
Surely that sales rep is expecting a nice commission from your project. Ask the rep to document how they meet each performance requirement. Are they able to provide the documentation? What are the performance criteria? Listing only the product name (a proprietary specification) is not sufficient.
We’ll try to demonstrate the value of performance specifications through the example below.
The story below is sadly a true case. In short, the architect didn’t specify performance, something else was installed, and a post-construction lawsuit results in exorbitant remediation costs.
Adam Architect and Erica Engineer are approached by Norm the Nurseryman, who sells green roofs. Erica informs Norm that their current design project needs to retain a 75mm (1.5 inches) storm and that they expect instant, excellent plant coverage. Norm is able to show several beautiful, convincing photos of plant performance, and he produces a glossy marketing brochure that claims some performance benchmarks. Adam and Erica are sold! Erica uses the values from the brochure in her calculations, and Adam issues a proprietary spec for Norm’s green roof system.
The construction contract is awarded to Corey Contractor, who is the second cousin to the grower, Gretchen. Gretchen also sells and installs green roofs, and Corey decides that he’ll go with whatever green roof Gretchen provides. Corey checks the spec, and it lists Norm’s product by name, but no performance criteria. When Corey sends submittals to Adam, Adam rejects the submittal for Gretchen’s green roof and says only to use Norm’s. Corey doesn’t like this and approaches Douglas the Developer for a change order if he is forced to use Norm’s system. After all, Corey based his contract price on Gretchen’s deep-discounted price. Douglas says: “no change order.” Adam tries to make the case that Gretchen’s green roof is not as performant, but Adam loses that battle because Douglas doesn’t want to approve of extra funds for something that was not specified. His words to Adam are: “If it was that important, you should have specified it.” Gretchen’s green roof is installed. It retains about 40% as much water as Norm’s, and the project does not meet its stormwater requirements.
About a year later, the project is audited by the local water and sewer authority. By this time Douglas the Developer has sold the property to Paul the Property Manager. The water and sewer authority notify Paul that the property is draining much more water into sewers than it was permitted for and that Paul needs to pay a $40,000 annual stormwater fee or provide some other remediation. Paul is floored! That is almost double the entire landscape budget for the property! Paul hires an attorney to investigate. The attorney collects all the publicly available files and determines that the project was permitted with one set of assumptions, then installed with a non-compliant project. With this information, Paul sues Douglas. In the end, the green roof is removed and replaced at the cost of approximately four times its original installation cost!
The names have been changed (obviously), and a few details have been simplified. But this story is true! I have been involved in a few such remediations, once as Norm, and once I prepared reports for an expert witness.
There is one additional detail in the story above that is worth noting: Norm didn’t produce actual documentation. Brochures are not documentation! Suitable documentation is a recent laboratory test report, indicating the specific manner of testing, date of testing, and test results. Falsifying test reports is fraud. Boasting a little bit (or a lot) in a glossy brochure is not normally illegal, and it is very common. Get the test reports during design, and definitely during submittals!
An alternate ending to the story above might be that Norm’s green roof was installed, but it did not meet the performance requirements he claimed in his brochure, which leads to the same replacement (but with a different party footing the bill).
Either version of the story above could have easily been prevented. There are many ways those construction specification horror stories could have been prevented, but the most straightforward and logical solution is to use clear performance specifications, with backup documentation.
“What?! Innovation?”, you say. Great ideas can come from anywhere, and often the best ideas come from smaller companies. Proprietary specifications often favor larger, established companies who can afford to send sales representatives into every architect’s and engineer’s office. Let’s examine another scenario, also based on many true stories.
Let’s say Erica Engineer talks with Wayne Waterproofing representative, who provides information about his green roof system. Erica likes what she sees, and uses that information in calculations, and submits it to Adam Architect, who writes a specification that includes all performance requirements but lists Wayne’s product as the only acceptable solution (i.e., a hybrid proprietary and performance specification).
The project goes to bid, and Corey Contractor gets a quote from Sara Startup Green Roof company. Sara’s green roof system meets or exceeds all the performance requirements, and her bid is 20% less than Wayne’s. Sara is able to do this because she just invented and patented a new technology that speeds up installation time, saving a lot of labor cost. Ultimately, Sara is not even seriously considered for the job, because Carl Construction Manager says: “Sara’s name is not in the specs!” Douglas Developer ends up paying more money, basically just because Carl and Adam were more impressed by the size of Wayne’s firm. This does not help advance the industry.
Montgomery County School District (bka) “School District in MD” has approved three different modules with a 10cm (4”) depth. For argument's sake, tray A retains ¼ gallon of rainfall, tray B retains 1.2L (½ gallon) of rainfall, and tray C retains 3.8L (1 gallon) of rainfall. But…there is no performance spec that dictates the expectations, the spec merely says ~10cm (“4”) green roof module”. The contractor, therefore, is free to choose between these three approved suppliers and asks for pricing, all three suppliers have a good record, and logically chooses the cheapest among them. Who can blame the contractor?
Even though stormwater storage is not necessarily related to cost, the more basic systems tend to hold the least, as is also the case in this real-life example. The contractor chose A. The unfortunate situation is the school to be covered with green is 11150m2 (120.000sqft) and is funded with tax dollars. We all paid for this stormwater tool, and for $0.50/sqft more the school could have gotten a tray that performs 4x as well. We could have captured 454000L (120.000 gallons) each time during a large rain event, but now each time it rains we have to do with just one-quarter of it.
Do you see now why performance specs are so critical?
Super, but let’s look at one other aspect of performance specifications that are often overlooked. Manufacturers have been known to provide performance specs loaded with a wide array of performance criteria, many of which are completely unimportant, but which only they meet. This is a sneaky, back-door approach to writing a proprietary specification disguised as a performance specification. Yeah, this is a dirty secret of the construction products industry.
For example, a manufacturer of a filter fabric might send the architect a spec that requires the fabric to be black, with a flow rate of 12.1 liters per minute (3.2 gallons/min) under a pressure of 8,000 psi. This manufacturer’s filter fabric might meet that spec, but are those necessary inclusions? If there is ever water pressure on the roof of 8,000 psi, people should be evacuating the building, and the filter fabric is the least of everyone’s worries. Should a filter fabric be rejected based on having properties different from those? If so, why? If not, then do not include those properties as performance requirements in the spec.
In summary, performance specifications are often ideal for green roofs, but those issuing the specifications should be able to justify the value of each performance requirement. A good performance spec should clearly - and concisely - state what the design team and owner really care about.
I am too. I practiced landscape architecture for 13 years, starting at a time when green roofs were still quite novel in North America. In my youth, when specifying green roofs, and many other less familiar technologies, I often used manufacturer-issued language without really understanding it. This led to change orders and too many teachable moments. Even though I administered construction contracts for over a decade, it was only upon moving from traditional landscape architecture to the construction supply industry did I truly understand how specifications work. Specifications should govern quality on a project. Specifications have been coopted to pre-determine purchasing contracts, in a way that does not necessarily improve project quality. Purple-Roof is a non-proprietary specification that endeavors to shift green roof design, specification, purchasing, and installation toward higher, verifiable quality standards.
We are fleshing out our specs for the optimal green roof assembly in any climate zone. As with any major effort, particularly when technologies are changing rapidly, this could take a while. If you don’t find what you need on our specs page, contact us for help. We also assist a number of manufacturers with their specs, and we can also direct you toward partners who have Purple-Roof-compliant assemblies with performance specifications.
Look for an upcoming post: "What to look for in a non-proprietary performance specification."