Consequences of Progress: When Mismanaged, Today’s Airtight Structures Welcome Condensation

By Glenn Ferris

There is an increasing frequency of condensation forming on windows and skylights these days and it’s due in part to new building practices that lead to extremely airtight structures, which rely on mechanical systems for air exchange. When systems are not adequately designed, or occupants use them in ways not intended by manufacturers, a highly humid indoor environment can be created. Extra humidity can cause condensation to collect on the surfaces of windows and skylights.

According to John Westerfield, marketing, web developer and code compliance officer at CrystaLite and chair of the FGIA Skylight/Sloped Glazing Marketing Committee, the push to build energy efficient homes is an underlying driver of this dilemma, but it is not the lone cause. “Another factor can be builders not familiar with the design and implementation of advanced HVAC systems utilizing indoor/outdoor air exchangers,” he said. “In the ‘good ol’ days,’ when one wanted to let in fresh air, they would open a window or skylight. In new construction, this is seen as wasted conditioned air, [that’s been] either cooled or heated. That’s why these indoor/outdoor air exchangers are utilized to transfer the thermal condition of the air to new air being circulated in.”

Air and energy exchange systems are highly efficient at recycling air with minimal heat loss, while also conditioning the air’s humidity levels. However, the system needs to be designed and configured correctly.

Sources of Condensation-Causing Moisture

Occupants of a building are the major source of airborne moisture—a large part of which stems from exhaled breath. Normal activities such as showers, cooking, dishwashing and even breathing release water into your air. Cooking, cleaning and bathing also release large volumes of moisture, much of which is exhausted by a bathroom or kitchen fan, but not all.

In the process, warm air can hold more moisture than cool air. As air decreases in temperature near a window, patio door or skylight, it cannot hold as much water vapor, just as it collects on a bathroom mirror. This results in condensation forming on glass and/or frames.

The solution to this issue might be as simple as education, Westerfield says. “Whether that means builders becoming more adept at designing and implementing these new building trends and equipment, or occupants understanding the new systems, education is key.” There may also be a large gap between the knowledge of the builder designing the system and their understanding of how occupants will use their new homes.

Plus, maybe the “good ol’ days” of letting free fresh air in from the outside by ventilating with an open window or skylight does have a place in the modern building world. Electric operators are readily available on the market to automate ventilation. Many of these electric window and skylight operators allow homeowners to customize programming for things like thermostat control, or the option to integrate with a home automation system.

Just as education is often the solution to many problems, so is balance. There should be a balance between homes that are constructed as airtight boxes and welcoming free, natural daylight and free fresh air in.

Glen Ferris is fenestration standards specialist for the Fenestration and Glazing Industry Alliance (FGIA).
gferris@fgiaonline.org

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