When the Building Envelope Fails
Selecting the Right Interior Finishes Can Minimize the Consequences
How far into the interior does the building envelope go? We design around questions of how far daylight, views, and heat will penetrate, but how far will failure penetrate?
The effects of envelope performance—or failure—may extend all the way through the building, especially in regard to moisture. Although elements closest to the exterior are likely the most affected, water has a tendency of finding its way deep into a structure. Are the interior materials resilient enough to withstand intruding moisture, or will they be damaged and compound the cost and disruption caused by the envelope failure?
Intruding moisture is a frequent cause of problems with indoor air quality (IAQ). Moisture combines with organic material used in building products to create breeding grounds for mold and bacteria. Where indoor air quality is especially critical, such as when hospital construction mandates an Infection Control Risk Assessment (ICRA), industrial hygienists may be required on the construction site to spot weaknesses where moisture has a potential to intrude or collect.
Moisture-related damage can be minimized if potential envelope failures are considered when selecting interior finishes. This proactive design guideline is not always heeded, however. Suspended ceilings with mineral fiber acoustic panels are widely used—despite the fact that they are notoriously susceptible to staining, sagging, mold and other water damage; they can even fall out of the grid, creating a mess and possibly injuring anyone or anything below. Wet mineral fiber panels are not recyclable, either.
A dramatic example is a church in Texas, that had to replace mineral fiber ceiling panels up to six times in just 30 years due to persistent roof problems.
Leaks can be caused by:
- Roofing and cladding failures,
- Voids in wall air barriers, dampproofing, and waterproofing,
- Blockages in drainage media or cavities in walls, and
- Defective flashings and sealant failures.
In addition, dripping water due to condensation can occur wherever cold surfaces contact warm, moist interior air. This occurs, for example, at thermal short circuits through insulation, glazing that does not have thermal breaks, and pipes, ducts and other objects that penetrate the envelope.
Even if mineral fiber panels do not require replacement, they can delay completion of a project and add to construction costs. The material is so susceptible to moisture damage that manufacturers recommend mineral fiber panels should not be installed until the building is fully enclosed and the humidity has had time to stabilize inside, a process that can take weeks or even months.
Thermoformed panels outperform mineral fiber panels in a range of industry-standard tests that relate to durability and resilience. Graph courtesy of Ceilume.
The composition of mineral fiber panels usually includes starch and cellulose, which are water absorbent and can feed the growth of mold and fungus, as well as other water-absorbent components such as expanded perlite. Visible stains and blotches in ceiling tiles may indicate bacteria and mold growth, which can impact IAQ. The U.S. Environmental Protection Agency (EPA), in Indoor Air Facts No. 4 (revised)—Sick Building Syndrome (Publication MD-56) lists “replacement of water-stained ceiling tile” as an example of “pollutant source removal” to reduce IAQ problems.
The Federal Emergency Management Agency (FEMA), Technical Bulletin 2—Flood Damage-Resistant Materials Requirement classifies common finish materials by their flood-damage resistance on a scale of 1-5, with 5 being the most resistant and 1 being the least. “Mineral fiberboard” has the lowest classification, “not resistant to clean water damage or moisture damage. Materials in this class are used in spaces with conditions of complete dryness.”
A More Robust Alternative
Try as we may, most buildings will experience some form of building envelope failure during their life. An awareness of this justifies using ceiling materials that are more robust—capable of performing without failure under a wide range of conditions.
Thermoformed acoustic ceiling panels, for example, are made of rigid vinyl that is impervious to moisture and does not support growth of mold or bacteria. They comply with FEMA Category 4 for flood-damage resistance, “these materials can survive wetting and drying and may be successfully cleaned after a flood to render them free of most harmful pollutants.” They can be washed with soap and water—a process that would destroy most mineral fiber panels—and are therefore approved for use in places where hygiene is tightly regulated (such as health care and food processing facilities).
Recent testing confirms the robust properties of thermoformed panels. ASTM D1308—Strength Properties of Prefabricated Architectural Acoustical Tile or Lay-in Ceiling Panels evaluates four criteria, 1) Hardness, 2) Friability, 3) Sag due to humidity exposure, and 4) Transverse Strength. Thermoformed panel strength properties are at least an order of magnitude superior to mineral fiber panels in all categories.
Thermoformed panels also have attributes that mineral fiber panels cannot approach, such as the ability to be used as drop-out panels installed beneath fire sprinklers, and light transmitting versions for creating back-lighted luminous ceilings. Thermoformed panels are stain resistant, acoustical, and up to 80 percent lighter than mineral fiber panels—so they can easily be substituted in most 2 feet by 2 feet and 2 feet by 4 feet suspended ceiling grids.
With a cost-competitive, higher-performing alternative available, the persistent use of mineral fiber ceilings suggests that designers are not factoring in the probability of even minor envelope failure, nor are they designing for it. Paying attention to a properly detailed envelope that can protect the interior from the outside world is paramount, but even with our best efforts, nothing is perfect. The use of robust materials that can survive a failure is also worthy of consideration.