Leaking Ductwork in Concrete Slabs

Common Causes

• The most common causes of leaking ductwork are poor installation methods and construction materials. For example, soil around ductwork that is not compacted can cause ducts to crack because of settlement of the soil and lack of structural support. Additionally, ductwork laid in small pieces, or not sealed against sand and water can eventually cause leaks. This is especially true for properties situated at the bottom of slopes or low-lying areas with high water table levels. During storms, melting snow and rain can cause flooding, further compromising ductwork systems under concrete slabs.

Materials and Performance

• Homes with cement-type ducts also are susceptible to unsealed issues. Some may contain asbestos fibers, which can affect air quality if ducts are not sealed and form cracks because of soil settlement. Alternative materials that used for ductwork underneath slab foundations include metal and corrugated pipes. Metal ductwork is no longer used in new constructions because of rusting problems, however. Today, polyvinyl chloride and other plastic materials are used because of their water resistance and smooth surface. Regardless of materials used, ductwork installed in concrete slabs should be equipped with waterproof joints to protect against moisture.

Dangers

• In addition to threatening the structural integrity of the home’s concrete foundation, leaks in cracked ductwork can lead to mold and bacteria growth. During heating seasons, hot air from furnaces worsens the problem by disturbing these particles and releasing them into the air via the home’s heating system. This degrades air quality and can causes allergy and other health problems for residents and occupants. Moreover, moisture and stagnant water sitting between slabs and ductwork exacerbate condensation problems on windows and other areas inside the home.

Solutions

• To clean and maintain ductwork, brush cleaning, vacuuming and pumping can dry and temporarily eliminate leaks and moisture problems. Consult an experienced professional who can pinpoint the cause of the moisture and contains experience cleaning heating ducts buried underneath concrete. Nationally syndicated newspaper columnist and “Ask the Builder” author Tim Carter also suggests diverting waterway from the house’s foundation using trench drains installed around the property. A second, though more expensive solution, is moving the ductwork from underneath the foundation to the attic. This minimizes the chance of leaks due to moist soils, flooding and other groundwater issues.