Climatic factors have a direct effect on the built and natural environments. As professionals in the design and construction industry, we make decisions on our projects that will influence this effect. Building envelopes offer a unique opportunity for our built environment to tap into the natural energy flows of a site, utilize local material palettes, take advantage of the lessons offered by a region’s indigenous building archetypes, or take a cue from natural systems with an approach grounded in biomimicry.

Photo courtesy of Douglas Adams and Browning Day Mullins Dierdorf

The Irsay Family YMCA at CityWay in Indianapolis, Ind.

Defining Building Envelope

The “building envelope” can be defined as that portion of the building that separates the interior and exterior environments in terms of energy (light and heat), water (in all its forms), air, pests and even people. As we consider the building envelope as a distinct part of a building, we recognize that its success and performance is in large part determined by the integration of its assemblies and components as well as the building envelope’s integration with the other building systems. The building envelope typically has at least six sides—four walls, the floor and the roof—and its performance relies on the characteristics of every side and especially their intersections.

Toward High-Performance

This article will focus on emerging trends in high-performance building envelopes that are viable in the market today. The term “high-performance” may seem a bit abstract—and it can mean different things to different contributors and stakeholders on a project. For the purposes of this article, high-performance is considered to exhibit four major aspects: safety, comfort, thriftiness and durability. Much of the building envelope’s contribution to a building’s overall performance is significant and direct, but this is not always the case.

A high-performance building envelope may make direct contributions to safety in terms of indoor air quality, but much of this contribution is actually indirect. For example, proper moisture management accomplished by the building envelope fosters improved indoor air quality by mitigating mold and mildew growth, but its contribution to this condition is indirect and certainly not determinant because plenty of other building elements and systems will contribute to indoor air quality as well.

Certainly, as the separator between environments, the building envelope is a major contributor to thermal, visual and acoustic comfort. As the separator from the exterior environment, the building enclosure manages the transfer of heat, light and sound.

The characteristics of an envelope assembly will impact energy performance and maintenance operating costs. The longer and the more distinct the environmental separation we ask the building to accomplish, the greater the stress we place on the envelope elements that serve to establish the environmental separation. However, a well-designed and constructed building envelope assembly can better withstand formidable climatic conditions and endure for decades.

The Major ‘Damage Functions’

We demand many functions from the building envelope. We prioritize the major damage functions of the building envelope in the following order:

• Liquid water (bulk and capillary)
• Airborne water
• Vapor
• Solar radiation
• Heat fluctuations
• Pests
• People

The first three damage functions are related to moisture management. Even in arid climates, water in all of its forms represents the number one challenge to building envelope performance, service life and durability.

Solar radiation—and subsequent heat fluctuations—can be an important damage function for certain types of exterior finishes, especially at higher altitudes and/or where incident solar radiation is high. Typically, solar radiation is a second or third order damage function in comparison to any of the other forms of moisture.

Pests, especially insects, can be a dominant damage function for building envelopes; however, pests almost always need a partner—moisture—to be a first-order threat. Water intrusion oftentimes results in deterioration and fertile ground for pests.

People, full-time occupants and transient visitors alike, and what they do (and do not do—e.g., maintenance) to both the building envelope and the mechanical systems of a facility can post major challenges to building envelope performance. Our building envelope assemblies are constantly subject to many forces which can inflict damage. If neglected, these points of vulnerability can become expensive failures.

A complete and adequate building envelope solution must withstand all of these phenomena.

Emerging Building Envelope Solutions You Can Use Today

The proceeding sections of this article offer a primer with regard to emerging, yet market-ready, solutions in building enclosures with an emphasis on wall systems. The building design and construction industry is changing at a rapid pace. Amidst the many developments, three key trends can be identified:

1. Innovations in technologies and products
2. Design performance modeling
3. Building enclosure commissioning

Innovations in Technologies and Products

There are many emerging innovative envelope solutions in the marketplace today. For the purposes of this article, we will consider four categories of envelope assemblies: rainscreens, glazing assemblies, green roofs/walls, and all-in-one wall assembly solutions.

As mentioned earlier, the building envelope must face a number of damage functions—and bulk water is public enemy number one.

In general, there are four basic approaches to bulk water management in a wall assembly:

1. Barrier: Barrier surfaces are designed to shed water without allowing any moisture penetration. Barrier-type exterior insulation finish systems (EIFS) exemplify the barrier system.
2. Mass: Traditional uses of concrete, masonry, timber structures and other solid assemblies that are capable of serving as hygric buffers will shed most bulk water, absorb the remainder, and slowly release the absorbed moisture as a vapor.
3. Internal drainage plane: The plane located between the exterior cladding and supporting wall that serves as a redundant moisture barrier. Stucco or clapboard walls will often contain a dedicated internalized drainage plane.
4. Rainscreen: Rainscreens manage moisture through cladding, an air cavity, a drainage plane and an airtight supporting wall system. These systems diminish the various forces of moisture-drive into a wall assembly.

Although they are becoming increasing popular in recent years, rainscreens seem to be the most broadly misunderstood assembly type.