Structural Problems

Moisture has been the number one cause of structural deterioration as long as there have been structures. Moisture in all its forms—snow and ice, wind-driven rain, and water vapor—greatly affect the performance of building materials. With unwanted moisture intrusion, masonry units and mortar can crack. When water enters brick, concrete, or natural stone, thermal expansion can cause the surface to peel, pop out, or flake off—a phenomenon commonly known as spalling, which is caused by excess moisture in the masonry that exerts pressure outward. Eventually, spalling can cause large sections of the masonry to crumble and fall off, potentially leading to structural damage.

Excessive moisture also results in wall rot, an extremely unsightly and unhealthy condition, as well as in disintegration of insulation and the staining of interior finishes. Other adverse impacts include deterioration and/or corrosion of the wood/steel backup studs, cladding, ties and reinforcements, which, left untreated, allow the water intrusion to increase and even spread, causing additional structural degradation or, in extreme cases, outright structural failure.

MOLD-A GROWING CONCERN

Photo courtesy of of Oldcastle® Architectural

To grow, mold needs the following: oxygen; a moderate temperature, generally between 40 to 100 degrees Fahrenheit; a food source; and, the single most important factor, moisture, which can come from leakage from the exterior building envelope or from high indoor humidity. If there is water damage to the structure, excessive humidity, water leaks, condensation, water infiltration, or flooding, mold will grow. When airborne molds find a damp indoor haven, the spores will begin to reproduce and morph from a nuisance into a dangerous health hazard.

Toxic mold is the source of a growing number of legal battles nationwide. Yet, mold has been with us for more than 100,000 years. Why has mold recently become such an issue in the built environment? The short answer is the change in building materials. Design and construction practices can have a profound effect on the potential for mold growth. In fact, continued efforts to reduce initial construction costs have resulted in increased use of lighter and/or organic materials that may provide food for mold. Paper-faced gypsum board, for example, has been substituted for plaster and lathe, oriented strand board (OSB) for plywood, or wood boards. Instead, products such as aluminum, molded plastics, fiber cement, and foam sheathings should be utilized. Pre-finished concrete masonry units manufactured with water repellent additives will also prevent moisture penetration without any organic materials.

While the quest for energy efficiency is a worthy goal, it has inadvertently created mold-related problems. Unless properly ventilated, tighter buildings are actually an ideal environment for mold growth, as are the givens of modern life, including wall-to-wall carpeting and air conditioning, which causes condensation. Mold arises in buildings because of the lack of “big picture” design. Changes are introduced in one component material or subsystem without evaluating their impact on other aspects of a building’s overall performance.

Mold can never be completely eliminated, but it can be minimized by limiting excessive moisture sources. The best formula for a mold-free building is to use a systems approach, quality materials, and a tight wall interior construction with proper operating ventilation and dehumidification systems.

Aesthetic Degradation

High on the list of aesthetic impacts of too much moisture is efflorescence, a white, powdery, crystalline deposit on surfaces of masonry, stucco, or concrete. Essentially, efflorescence is the result of a salt within the masonry unit itself that has been dissolved by excess moisture and has migrated to the surface of a porous material, where it forms that unmistakable white bloom as the water evaporates. According to the Masonry Institute, three problems must exist in order for efflorescence to occur:

1. There must be water-soluble salts present somewhere in the wall.
2. There must be sufficient moisture in the wall to render the salts into a soluble solution.
3. There must be a path for the soluble salts to migrate through to the surface where the moisture can evaporate, thus depositing the salts which then crystallize and cause efflorescence.

Even though sulfates may be present in a masonry wall, they must be dissolved by water in order to result in efflorescence. No moisture means no migration of sulfates to the surface. Certain conditions, however, will aggravate the potential for efflorescence. If the block has been exposed to cold, rainy weather during storage, for example, or to prolonged or heavy sprinkling, or if the structure has been poorly designed in terms of drainage and moisture control.

Health and Safety

According to the Department of Energy Building America Solutions Center, “Moisture is not often thought of in terms of occupant health and safety. Yet indoor air quality professionals consider moisture to be a ‘pollutant’ that can have a significant impact on the occupants’ health.” Excess moisture causes the growth of bacteria, which can generate new or worsening odors and harmful gases inside the building envelope. The effects can aggravate such conditions as asthma and allergies and, in some cases, result in cancer and birth defects. Airborne moisture is ripe for dust mites and roaches whose droppings exacerbate allergies and whose appearance necessitate the use of insecticides, which have their own deleterious effects. One of the most dangerous threats to human health and welfare from excess moisture in the building is mold. The subject of widespread media coverage and a surging number of cases across the country, mold can have severe consequences, and is extremely challenging to remove. Property insurance does not cover all mold damage, and insurance companies are scaling back on coverage and are not writing new policies in some states. Liability policies are now including mold exclusions. For further information on the growth and consequences of mold, see accompanying sidebar.

Photo courtesy of Oldcastle® Architectural

Photo courtesy of Oldcastle® Architectural