Of Elephants and Windows
An old fable from India tells of a group of blindfolded men who, having never seen an elephant, were asked to conclude what an elephant is like based on touch alone. Each, having touched the elephant in various places–trunk, ears, belly, leg, tail–respectively describe the elephant as like a snake, palm leaf, wall, tree trunk or rope.
Some in our industry– be they manufacturers, dealers or specifiers – have on occasion been guilty of just this sort of narrow perspective based on prejudices about materials and performance priorities. In general, such parochial myopia has been improving in recent years, although when newer materials come along, the zeal of their proponents sometimes reverts to such arguments.
To better serve all of our stakeholders and buying influences, we must remain aware that the big picture is what matters. The big picture of window performance is not just U-value. While a cause célèbre today, and the lynchpin of high-profile energy-saving programs, from the American Recovery and Reinvestment Act (“stimulus package”) to Energy Star, there remain other considerations that may dictate trade-offs. These range from solar gain to resistance to hurricane-propelled debris, forced entry and bomb blasts. Priorities rightly vary by project, as do approaches for accommodating them.
The big picture of window performance is also not just glass. It recognizes that a window is a complex, interacting system of components—framing, finishes, glazing, screening, weatherstrip, gaskets, sealants, hardware and screens—that must perform properly over a long service life.
And most importantly, the big picture of window performance is not discerned by debating the alleged merits of the different framing material.
Common though typically unsubstantiated claims and counter-claims still circulate—wood windows are attractive and energy-efficient but are high-maintenance; vinyl windows are energy-efficient and economical but lack strength; aluminum windows are structurally strong and low-maintenance but have poor thermal performance; fiberglass is strong and energy-efficient, but currently not practically recyclable and relatively expensive. These stereotypes often reflect unsupportable prejudices rather than absolutes of performance.
When we remove the blindfold, we see that each framing material offers its own unique performance characteristics. For example, wood windows, when provided with exterior aluminum or vinyl cladding (as are most designs today) preserve their interior appearance while addressing the exterior maintenance problem. Vinyl window profiles are engineered with a multi-chambered framing design for strength that can be further bolstered by metal reinforcing members. Aluminum windows, by using structural thermal barriers, exhibit thermal efficiency that meets the majority of existing energy codes. Fiberglass processing innovations are bringing costs down.
In other words, all profile materials offer special advantages for dealing with the performance challenges posed by climate, building design, buyer preference or budget for various applications. The material controversy is rendered virtually immaterial when one stops comparing the basic characteristics of isolated samples of unsupported material and concentrates on the performance of the complete window unit.
Any given window product, regardless of material, can be well-designed and well-made, or it can be poorly designed and built. The distinction between “high-end” and “low-end” products is based not on its framing material, but on the performance level that the products are designed to meet–something that goes beyond clever advertising or competitive claims. The issue is quality, not material. Those who claim superior performance based solely on the framing material are grasping blindly at the elephant’s tail.
Today’s performance-based, material-neutral window standards, AAMA/WDMA/CSA 101/I.S.2/A440-08 (NAFS-08) or its predecessors, and the rigorous laboratory testing that backs AAMA certification to those standards, take into account the unique properties, strengths and weaknesses of all material types. Given equal performance of the overall unit, the choice basically reduces to one of operating features, appearance, brand name, cost, green attributes or other factors for the specific application, rather than determining which is better at some absolute level.
Validated test data should always be utilized as the basis for comparing performance claims. The marketplace can then use such data or third-party performance certification to properly evaluate the products based on the demonstrated performance of the entire assembly, not that of one specific piece of the puzzle. To do otherwise is equivalent to ignoring, well, that elephant in the room.