Can You Solve This Architectural Conundrum?

Henry Gifford is what is known as a building scientist: He studies how buildings work and, just as important, why some don't. He has written and published a remarkable book called Buildings Don't Lie, nearly 600 full-color pages stuffed with information, infrared photography, diagrams, and—the best part—quizzes to test your knowledge.

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The book is as beautiful as it is exhaustive, covering air flow, water, light, sound, fire, pests, ventilation, air quality, and a lot more. We'll be covering the subject of building science more in the magazine soon. In the meantime, here's a quiz from the book:

Question: Why is water vapor condensing onto only one of the windows? And why in the middle of the pane only? And which surface of which pane is the water condensing on?

Clue: The photo below was taken during the winter.

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Got it?

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Answer: The window in the photo has two panes of glass. Multi-pane windows are built with an airtight space between the panes. In the middle window, the air barrier has failed. It is allowing water vapor to get into the space between the panes. The condensation is occurring only in the middle of the pane because the frame of the window conducts much more heat (from indoors) than the glass, and the heat is heating the edges of the glass above the dewpoint temperature, while the middle remains colder than the dewpoint temperature.

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The water must be condensing on one of the surfaces between the panes because otherwise the water would evaporate into the indoor or outdoor air. This leaves on the question of which pane the water is condensing onto: the pane on the outdoor side, because that pane is colder during the winter.

Henry Gifford has 25+ years experience making buildings energy efficient, using common sense approaches. You can buy his new book, Buildings Don't Lie, right here.

Source: Can You Solve This Architectural Conundrum?