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Building Science

Callback Prevention by Steve Easley
(Excerpted from Building Edge Magazine, November 2004)

As a building-science consultant, my job is to help builders understand how to reduce callbacks and lawsuits due to construction defects. Callbacks and defects account for the loss of billions of dollars in lost revenue every year for homebuilders. Reducing this loss starts with understanding and controlling some important principles of how moisture, air and heat move through a house.

The Not So Big Showhouse demonstration home has been built as a practical learning center to exhibit best-practice home design and construction techniques. This project is one in a series of demonstration homes designed to meet specific environmental demands in regions around the country. In this case, we have set out to build a home that performs optimally in the humid, hurricane-racked southeastern U.S.

Southern Discomfort
Throughout the Southeast, high heat and humidity create an aggressive climate for houses. Not only do frequent rains and high winds force water into walls, but the average relative humidity levels in this region typically reach above 70% year round. Under these conditions, walls rarely have a chance to dry.

If water soaks into walls that are slow to dry, problems such as peeling paint and mold growth can show up in a few months, and rot can take hold immediately inside wall cavities, although problems may not be visible for years. Mold and rot flourish whenever water or moisture is available, and regions with high relative humidity, where the drying potential is low, are at greatest risk.

To compound these already difficult circumstances, frequent air conditioning keeps interior surfaces cool. This means that warm, moist outside air which is driven into a wall begins to cool. If it reaches the dew point, it may condense inside of the wall. Poorly installed HVAC equipment and duct leaks can pull warm humid inside, increasing the chances for moisture related problems.

Not So Big Solutions
The solutions to these problems are not difficult, but they demand attention at every phase of the building process. In the Not So Big Showhouse, we used Building America's Houses That Work II information to help us pay particular attention to detailing the exterior walls to control the entry of moisture.

For example, starting at the sill plate, we install Protecto Premium Energy Sill Sealer to seal the vulnerable transition between the slab foundation and wall structure. The walls themselves are designed to be as energy and resource-efficient as possible using Insulspan structural insulated panels (SIPS). These panels come 4 and 8-feet wide and in lengths from 8 to 24 feet, so large areas of insulated wall can be erected quickly, using far less lumber than a conventional stick-built wall, and with far fewer air leaks. In addition, there is no cavity in the wall, so there are no surfaces that could reach the dew point, making it virtually impossible for condensation to form inside the wall.

In the Orlando climate, wind-driven rain is likely to get blown through numerous cracks or porous openings of the stucco and fiber-cement siding on this house. While these materials are themselves resilient to moisture, the surfaces under them must be sealed to prevent moisture and air migrating to the interior. To do this, the house has been carefully wrapped in Tyvek, which keeps water out, but allows any incidental moisture that gets in during construction to dry. In addition to this weather barrier, all penetrations - windows, doors, exterior lighting fixtures, and vents - are carefully flashed with Tyvek Flex Wrap and Straight Flash. These flashings are made of butyl rubber, which bonds better and lasts longer than other common flashing materials.

Installed properly, this highly energy-efficient and tightly sealed building envelope can eliminate nearly all of the worst moisture and air problems. Combined with state-of-the-art cooling and ventilation appliances to control the flow and temperature of air inside the home, there are very few opportunities for callbacks.

Steve Easley specializes in solving building science related problems and helping builders reduce construction defects and call back costs. To learn more, visit the Not So Big Showhouse at the 2005 International Builders Show.