How environmental concerns shaped modern architecture.

(The following is Part Three in a seven-part series on the growing rate of mold detection, remediation projects and litigation in the US presented by the experts at the Environmental Health services group at LZA Technology, a division of The Thornton-Tomasetti Group.)

In the last installment, this series discussed how the lack of knowledge of the utilitarian underpinnings of the elements of architectural style has resulted in the creation of architectural time bombs in every community in America.

The symptom of the time bombs is mold. The cause of the mold is unmanaged water in the building environment.

Once architectural devices lost their functionality, the necessary understanding of how and why they functioned was lost.

Architects and builders were freed of the requirement that they understand how buildings function, and were free to simply decide how buildings look. Their product pleases the eye, but they do not function properly.

One of the most influential analyses of American construction is James Marston Fitch's "American Building: The Environmental Forces That Shape It." An aspect of the environment that Fitch points out shaped architecture is the maintenance of a comfortable interior temperature and humidity.

In the past, lightly built homes with large openings and deep overhangs maintained a comfortable environment in the warm, moist south.

Massive homes with small openings maintained a comfortable environment in the Southwest. Clapboard homes in New England were made livable by a large central hearth, large windows, and shutters.

Today, with the rare exceptions of solar homes or "green" homes, the interior environments of most buildings are maintained by the brute force of furnaces and air conditioners. It would have struck our forefathers as ludicrous to build thin, all-glass buildings in New York, since occupants would freeze in the winter and broil in the summer.

A Cape-cod bungalow makes little sense in Arizona, since it becomes a small Dutch-oven all summer. Yet both of these are perfectly rational choices today, because we have environmental equipment that can overwhelm the effects of the natural environment.

This appears to be benign enough, since it makes certain environments livable. But the original functionality of the building enclosure and the operation of the environmental equipment have become disassociated. The ornamental architectural style of buildings did not evolve simply in response to a need to keep the interior dry, it also evolved to maintain a livable interior environment.

These two aspects of style were indivisible. Now, it is often the case that the architectural style is in direct conflict with the environmental equipment struggling to maintain a livable environment.

For example, in order to make a new Italianate stucco villa with large sliding glass windows livable in Miami in the summer it takes a lot of air conditioning and dehumidification. This creates miniature iceboxes sitting in a tropical environment.

This is not a "natural" phenomenon. It is entirely artificial, maintained by electric bills and insulation. It is also entirely modern. Traditional architecture was not faced with this combination of conditions, and obviously no traditional method of responding to its side effects evolved.

What are the side effects of this little cold world sitting in the Caribbean air? Visualize a large glass of ice tea sitting on a table on a veranda in Miami in August. Soon it is covered with water that is condensing out of the air, and before long it is sitting in a puddle of water. Now visualize the house as the glass of ice tea. Soon, it could be covered with water as well.

It is a fact of nature that when warm air cools, the vaporous water that is dissolved in it cools off, and turns back into liquid water. Therefore, as a general rule, cool air is dryer than moist air. The previously invisible vaporous water in the warm/moist air becomes liquid and is no longer suspended in the air. It ends up on the table around the glass of ice tea. In an air conditioner, the vapor cools on the cooling coils, turns to water, drips down into a pan, and is piped to a drain.

This is why dehumidifiers have to be piped to a drain or the pan has to be emptied every so often. But if warm air cools off while it is inside of a wall, the vapor will revert to water inside of the wall as well, and the water will be deposited in an uncontrolled, unanticipated location.

This is only a problem if warm/moist air is being pulled into a cool/dry environment through a wall, resulting in condensation. But why is warm/moist air being pulled into or pushed out of the walls?

There may be exhaust fans in constant operation, or the air conditioning equipment may actually cause some areas to be under a slight vacuum. Pressurization of buildings can inflate buildings, pushing air out through the walls.

Tall buildings create their own stack effect that pulls air into the ground floors.

How does the air get into the walls? Buildings generally are not air-tight.

Air can seep in though cracks in the walls and around gaps in the window framing, and is pulled down from the attic or up from the floor.

But moisture can move even if there is no air movement at all. It moves through the very obscure means called vapor pressure.

This is the natural force created when a high concentration of moisture that is dissolved in a body of warm/moist air attempts to equilibrate with a low concentration of moisture dissolved in an adjacent body of cool/dry air. This is no more than the intuitive concept of "water seeking its own level." This phenomenon is trivially apparent in the fact that potato chips get soft eventually if kept in a paper bag, no matter how tightly it is sealed. Vapor pressure forces moisture through the paper until it is as moist within the bag as it is without despite the fact that there is negligible air movement.

So in the example of the Italianate mansion in Miami, the water vapor from the exterior infiltrates through the exterior wall either through air introduced through gaps, or by means of vapor pressure.

within the wall, it gradually cools off, and the water vapor condenses out and reverts to liquid water. All four conditions are now met for mold growth.

There are spores within the wall, as there are everywhere in the environment.

There is ample organic matter in the studs and paper facing on wallboard. It is the right temperature. And now there is liquid water to light the fuse of mold growth.

Don Erwin, R.A., a rice president of LZA Technology, is an architect specializing in forensic investigations and analysis of existing building performance.