Volume 46, Issue 2
Letting Windows and Walls Do the Jobs They Are Supposed to Do
In 15 BCE, Vitruvius encouraged us to build well and to incorporate utilitas, firmitas, and venustas. Sixteen hundred and forty years later, Sir Henry Wotton reinforced this ancient mantra in The Elements of Architecture as “commodity, firmness, and delight.” These salient elements are still vital to exemplary design—reflecting the foundation of the green building movement. Surprisingly, though, they are often forgotten, corrupted, or removed from service.
The green revolution isn’t about refitting our buildings with something new; far from it. Our green revolution might better be referred to as a green revelation, offering us an opportunity to rediscover, relish, and refine inherent strengths and timeless features: those architectonic elements embodying performance, durability, and beauty.
As our lives are increasingly dominated by the magic and inventiveness of silicon-based technological advances, it is easy to lose sight of the magic and inventiveness of many architectural advances embedded in our buildings that are tied to nature, setting, and local environment. Exploring just a few of these hidden gems reveals how fundamental they can be to our comfort and enjoyment, not to mention how beneficial they are to a building’s efficiency. These simple, passive systems are often overlooked, and the corruption of even one can have unintended widespread negative consequences. Once rediscovered, however, we find that virtually all of these features can readily be put back into service.
Let’s consider some common issues affecting the interrelationship of light, air, and thermal comfort. In the 1970s the oil crisis sent shockwaves through religious properties, causing vast expanses of stained glass windows to be sealed with polycarbonate sheeting. This led to the widespread decimation of a profound collateral system: window operability, particularly clerestory windows perched high above the nave. Forty years later, religious property owners now revel in the simple pleasure of removing this sheeting—which discolored and deteriorated years ago—and re-opening the windows. Why? Open windows induce convective (updraft) currents, which are especially important in sanctuaries and in large assembly spaces. Convective cooling, which allows hot air to escape from the top while encouraging cool fresh air to enter from below, might be viewed as the “original” air conditioning system.
Commonly mischaracterized as “protective,” polycarbonate-sheeting-sealed windows have resulted in damaging lead caming and window frames, raising levels of energy consumption and maintenance, and increasing capital expenditures for mechanical equipment to overcome excessive heat, moisture, and stale air. Sealing windows traps an air space between the sheeting and the original window that can become super-heated, causing the air to expand. The combination of pressure and heat causes lead—the softest material within the assembly—to deform. Windows bow and glass cracks or falls out. As the sheeting deteriorates, less daylight is admitted, increasing the need for artificial lighting and the costs associated with fixtures, upgrades, and electrical service. Also, degraded plastic sheets that become etched, fogged, and yellowed compromise the inspiration of stained glass windows. Art glass is dependent on abundant light to convey its message. Most of all, sealed windows interfere with the passage of fresh air and the introduction of natural ventilation, so critical to interior thermal comfort. Thus, we turn to mechanical equipment to make up the difference.
Just as a loss of natural ventilation increases dependency on mechanical equipment, loss of inherent insulating properties of the exterior envelope increases our reliance on heating systems. Thermal benefits of exterior masonry walls—in particular, the attribute referred to as “thermal lag”—are often overlooked because they cannot be seen and are not widely understood. Thermal lag is a natural system of buffering extremes in temperature between interior and exterior. Dry walls in good repair are stellar thermal insulators; wet walls, or those in poor condition, are not. Rather than repair walls, though, our tendency has been to add insulation or turn up the thermostat.
Contrary to current trends, adding insulation to masonry walls can impart disastrous consequences, affecting both thermal comfort and moisture management within walls. Regarding thermal comfort, insulation negates the ability of masonry walls to buffer the interior from exterior via their innate ability to absorb the sun’s radiant energy, store it, then slowly release it to the interior hours later, when it’s most desirable. Insulation also has the potential to shift the dew point within masonry wall construction, causing condensation to collect and, in winter, to freeze. Such conditions lead to rampant mold growth, deteriorated wood framing, and spalled mortar and masonry. Saturated insulation loses its ability to insulate, and defeats the whole purpose of adding it. Simply put, exterior masonry walls work best when they are in good repair, with a maintenance program that ensures gutters and downspouts do not overflow, mortar is selectively re-pointed, and stone walls are injection grouted wherever internal voids exist.
The more we understand our buildings, the better we recognize key attributes that are both interrelated and inseparable. The sweet spot of holistic sustainability may be found when they are working in concert in a balance of performance, durability, and beauty. This is truly a revelation.