Letters

In a recent issue of BD+C (January 2007, p. 79), you authored an article about the importance of air barriers in building construction.

First of all, I congratulate you for bringing this issue to the forefront. It is high time for the industry to learn the comprehensive nature of building envelope design and to challenge the idea predominant in the field that exterior wall design is a simple thing that anyone can do. In fact, most professionals don't know how to put together a composite wall system using today's new materials. I know this after more than 30 years of teaching environmental technologies to architects.

However, there is one correction I would like to suggest. The second paragraph in your article states: “But recent theories suggest that there's a third culprit in the moisture intrusion mystery—air.”

I would like to reassure you that the idea that air can carry moisture through wall systems is not new. It has been known for decades and is backed by studies conducted by ASHRAE, DOE, and the Canadian Wood Council. One would only have to Google the term “air barriers” to find the extent of literature and research available to the industry on the subject.

As I stated earlier, the complexity of a good composite wall design is often overlooked. The design has to take into consideration not only the climatic conditions of the building site, but also the thermal properties, vapor retardance, and air barrier characteristics of each material used in the construction.

In addition, the pressure relationships between the interior and exterior need to be considered. In complex applications, such as labs, swimming pools, and kitchens, the pressure relationship between the interior spaces should be factored.

Care must also be taken to avoid doubling the vapor barrier in the wall system, thus trapping the omnipresent moisture. Since most air barrier materials are also vapor retarders, the possibility of creating a double vapor barrier is great.

Finally, it's important to note that air movement through a wall can both help and hinder vapor migration. Depending on the direction of vapor movement, air flow will have an impact on the rate of moisture removal from a wall during the diurnal cycle.

For example, during a summer night, vapor is trying to exit the wall toward the outside, and a strong air movement in the opposite direction will slow down the process. Air movement parallel with the direction of vapor flow will help with moisture removal. Therefore, the vapor retardation characteristics of the air barrier will be significant.

Stephen J. Vamosi, PE

Professor emeritus

University of Cincinnati

Your recent article featuring the “40 Under 40” superstars (January 2007, p. 27) is quite interesting and very informative.

However, there are a few of us that are over 80 and still working full time in the design-build arena. This younger generation is loaded with talent, and I'm still learning.

When I started doing design-build work in the mid-1960s, we learned through attrition and mistakes. There were no organizations like the Design-Build Institute of America. It was the most interesting of times, to say the least.

I always look forward to the next day and all its rewards and challenges.

Bernard Stertzer

Director of design, VP

Harper Construction Co.

San Diego

In our January 2007 article on hurricane-zone construction (“9 Tips on Anchoring Rooftop Equipment for High-Wind Events,” p. 75), lightning protection systems were erroneously referred to as lighting protection systems. We regret the error.