Solid as a Rock

Nov. 1, 2002
Selecting a high-performance material can increase the likelihood of creating a healthy environment for learning.

The school construction boom in the last decade forced some districts to build faster and more cheaply. Speed of construction combined with cost savings, however, did not always equal success for long-term needs. It has resulted in air-quality problems in many schools.

For these schools, the building health crisis is just beginning. Roof and wall leaks are the leading cause of moisture entering a building. Moisture leads to mold, which can enter a building's heating, ventilation and air-conditioning system, with dire effect on indoor air quality.

Designers should choose materials that will be “forgiving” when moisture enters a building. Because of the moisture problems in some schools, more officials are considering materials of substance over speed. Masonry materials can enhance the health and quality of schools.

A building envelope is made up primarily of roof and wall systems. The proper choice of envelope material is critical in controlling moisture. Concrete block, brick and cast concrete can be cleaned and dried easily, and are not destroyed by mold. Although masonry materials do not counteract moisture problems, they are more “forgiving” when building leaks occur or plumbing fails.

Properly designed masonry provides many levels of protection. Given the decline in the skill level of available labor trades, schools must consider designs that reflect the realities of the final product. Pushing material to perform beyond limits in a “perfect-world” scenario is unrealistic. Instead, planners should focus on designing a building with materials that can sustain moisture breaches without catastrophic results.

In addition to avoiding mold more effectively, buildings constructed with masonry have the advantage of requiring less annual maintenance. Selecting materials such as face brick, concrete block and other similar materials allows a school to focus its limited maintenance budget on issues such as HVAC upkeep, rather than wall repairs and replacement.

Exterior sustainability

Using porous and paper-based products as the substrate for exterior wall systems has given rise to many of the mold troubles in schools. Even with the best detailing and installation, builders must acknowledge the realities of construction.

Walls typically are not sealed daily. Most exterior walls are exposed each day to some degree to moisture, heat, humidity and oxygen. These are the perfect ingredients for mold growth. Thus, these buildings are potential trouble even before the building opens. Combine these conditions with normal building movement, roof and plumbing leaks, and the result is long-term building health risks.

When mold becomes a problem, it typically is the result of prolonged exposure to moisture that comes into contact of a porous or paper-based product. It is important to act immediately and deal with any roof, wall or plumbing leak. The leak should be stopped; the area should be dried and checked for damage. Most porous or paper-based products will have to be removed. For replacement, consider a material such as concrete unit masonry, clay masonry or a concrete backer board product; they are better able to withstand moisture.

Where else to check

Other common areas to check for mold include classrooms with sinks; it can grow around and behind sink edges. Sink splashes should be properly sealed and checked bi-monthly. Check below sinks, too, to make sure water has not seeped from the sink or countertop into the wall.

Be aware of the problems that building occupants may cause. Expansion and control joints require proper sealant to protect against students who scrape at the joints as they pass by, making the joints more vulnerable to rain and moisture. Parent organizations often work to add beautifying landscaping features next to school buildings, which can cover drainage holes and cause moisture to back into the base of classrooms. To avoid this possibility, keep all weep holes open and clear.

It also is important to maintain HVAC systems and never shut down a system completely during non-use periods. The days of “closing the school” for summer break have passed. Maintaining a maximum of 60 percent relative humidity inside a building will reduce the risk of mold and other problems that can develop when humidity levels are high and air movement is low.

School districts, architects and contractors must demand that quality, not speed and initial cost, become the core of school construction standards. Further, maintenance workers must maintain buildings vigilantly and address moisture breaches immediately.

Increasing the focus on the building envelope and site conditions, such as proper slope and grade, must become part of a school's daily maintenance regimen. When considering new school construction, look at all costs, including the life-cycle costs of maintaining the building. Given that the exterior envelope accounts for 12 to 20 percent of the project cost, investing in the best assembly possible likely will cost little initially and pay off in the long term.

Until those priorities are embraced, schools will continue to face mold problems. The cost of these problems will far surpass the initial time and money required to build solid as a rock the first time.

Sidebar: Some masonry system details

  • Eight-inch CMU minimum backup Wythe with face brick or CMU veneer clad exterior face.

  • Fill interior CMU with foamed-in-place insulation or provide board insulation in the cavity.

  • Cavity width should be a minimum of two inches.

  • Provide a vapor barrier. Placement of this barrier depends on project location and climate.

  • Use modular brick sizes from detailing and installation issues.

  • Provide through wall flashing at wall base, high-to-low wall conditions, door and window heads/sills and lintel conditions.

  • Provide weeps at two feet to eight feet maximum, and coordinate so weeps do not occur below grade.

  • Provide expansion joints in brick and control joints in concrete unit masonry — 20 feet maximum exterior conditions and 25 feet interior conditions.

  • Remember that concrete products shrink as they cure, and clay products expand as they cure. If the two products are used in the same wall, provide a bond breaker to allow for movement between the products.

  • Provide proportion mortar spec — Type S or N as required for design condition. Do not allow the use of masonry mortar.

  • Regulate the use of a power washer to clean masonry — limit pressure to 1,200 PSI and nozzle-type to 15-degree tip minimum to help prevent damage in the cleaning phase.

  • Hold a masonry pre-construction conference prior to any work. All parties can discuss expectations of quality, details and workmanship.

Huckabee, AIA, is CEO of Huckabee Architecture, Engineering, Program Management, Fort Worth, Texas, which provides planning, design and management of schools, primarily with masonry.

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