Currently, I have been on my “soap box” relating to the topic of “Engineering Judgement” letters in the façade and curtain wall industry. Unfortunately, I see too many written statements that often lack both engineering and judgement. (On a related topic, “Value Engineering”, often a synonym to some for “cheap” and without engineering, tends to drive some of these statements, but I digress, as that topic is for another blog.) “Engineering Judgement” is the term typically used when someone wants or needs a letter, or a written statement, to show the comparison or similarity of an existing product, system, or assembly, to a tested standard. This can be a direct comparison of the particular system application itself versus the industry standards; or comparison to a different but similar project or system.
One such example concerns comparisons to the NFPA 285 “Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components.” Another example would be comparing fire-safing assemblies to test specimens; using a firestop to inhibit flame spread between floors between the back of the curtain wall and the slab edge.
So what is my issue? There is nothing wrong with a legitimate engineering judgement approach. In fact it is not always necessary to test every component or system on every job. But too often I see engineering judgement letters that stretch reality in an effort to satisfy a requirement in a spec, to make a sale, or to be the low-cost line item in a bid, but without credibility. (It’s akin to using a photocopier to make a copy of another copy, which has been made from an earlier copy of the correct, clear, original version.)
In one instance, I recently read a judgement letter comparing a particular exterior cladding system and its test specimen to the NFPA 285 test. The product information indicated that the system comprised of their material was “NFPA 285” approved. Upon further review it was found to be benchmarked against an old UBC standard that wasn’t anything like the NFPA specimen. In fact, there was never a single NFPA test performed to which one could compare. Sadly, an engineer had written a statement saying that it was the same or equivalent; that the data could be extracted to validate the same results. This was not close to reality.
Often, we also find engineering judgement letters on the topic of fire-safing that leave much to be desired as compared to tested assemblies. In fact it may be the most common type of judgement letter I see. A letter from a sales staffer or manufacturer’s representative on company letterhead alone doesn’t mean something qualifies as acceptable.
As a further comparison, in the surveying world it is important to benchmark from a given reference point. You don’t benchmark from a different point or construction stake from one marker to the next. This same principal applies to engineering judgement. The judgement should be referenced to a tested standard, not a reference of a reference to a standard that loosely applies.
We need to think more critically about engineering judgements. Remember, we are installing REAL products and assemblies on REAL buildings with REAL people inside and outside the structure. Safety and comfort to occupants and pedestrians is a key issue, along with durability. It would be beneficial if more realized that a building code is the MINIMUM acceptable standard required for the built environment, not the maximum. Compare what you receive with what the standard defines. Hold everyone accountable to the same standards. Keep the playing field level. If we want to advance the glass, glazing, façade and construction industry at large, we have to show it with our actions and integrity; holding ourselves and our industry to higher standards and accurate reporting.
John Wheaton is the founder & co-owner of Wheaton & Sprague Engineering, Inc., also known as Wheaton Sprague Building Envelope. The firm provides full service design, engineering and consulting services for the curtain wall/building envelope/building enclosure industry, and works at “Creating Structure” for clients. He can be reached at email@example.com and on Twitter, @JohnLWheaton1.
The opinions expressed here are those of the individual author and do not necessarily reflect those of the National Glass Association, Glass Magazine editors, or other glassblog contributors.