We've already discussed in Chapter 9 how climate change has been moving the tropical zone northward. This has the same effect as taking a building in the north and moving it southward. Each year that the climate shifts our northern cities are becoming a little warmer, and a little more humid. This is likely to result in the northern buildings with their interior vapor barriers trapping moisture during the summer months for a longer period of time. The moisture-tolerant building will be more
likely to make it through to where the season changes and the moisture flow again becomes favorable. As these climate shifts occur there will come a point where some homes will no longer be able to handle the changes and will begin to deteriorate. The buildings that have the lowest moisture capacity (those with metal framing) are likely to be the first to exhibit problems. Wood-framed buildings and especially those built of solid masonry should have a greater resiliency.
Assuming global warming only warms without cold swings, the buildings most likely to experience difficulty are those that have been built with interior vapor barriers in all of Canada and the northern parts of the US. This vapor barrier is helpful during the cold part of the year, but during the summer, especially if air conditioning is being used, the moisture
How Illinois's climate is projected to change according to the Hadley Centre model, developed by the Met Office in the United Kingdom. Its summer climate would become more like West Virginia's in 2030 and more like coastal Virginia's and North Carolina's in 2090.
levels in the walls will begin to climb. Indoor air conditioning may do a great job of reducing the indoor humidity, but won't have an effect on the humid outdoor air flowing into the wall cavity behind the vapor barrier. When moist air hits the cold vapor barrier against an air-conditioned wall, moisture condensation will begin to form inside the wall cavity. Turning off the air conditioner would help save energy and reduce this risk, but as extreme heat waves become more common turning off the air conditioner may result in the need to temporarily abandon unbearably hot buildings.
If warming was all that happened with global warming, then homes in the southern states should be in pretty good shape for dealing with climate change, but that's not how climate change appears to be progressing. Instead, we have swings with unexpected and extreme cold weather events. If you hear that Florida citrus growers have to protect their crops against frost, you can be pretty sure that homes in Florida with their vapor barriers on the exterior of the building will be accumulating moisture in the walls during cold snaps. The warm indoor moisture will try to dry to the cold exterior. When it hits the cold exterior surface of a wall that has reduced permeability, that moisture will also begin to condense and potentially lead to problems if the cold snap lasts more than a few days.
- You might think that buildings in the middle, mixed-climate portion of the country would do better than those in "Adaptive capadty ¡s the aWNty of a system the north or the south since they would already be built to to adjust to climate change (including withstand fluctuations. Not so. A large number of buildings c|imate variabi|ity and extremes)to in mixed-climates have been built with vapor barriers to moderate potentia| damages,to take respond to the energy crisis and are already poised on the advantage of opportun¡ties, or to cope brink of moisture disaster. Unless they pay special attention, with the consequences." most people won't know what is going on inside their walls
(IPCC 2007 page 20 until the problems have developed.
Summary for po|icymakers) But there is hope. New types of "smart" materials are --being developed and will hopefully be marketed before these problems become completely out of control. The ideal "smart" barrier would have a variable permeability that could also change the direction of moisture flow as necessary to accommodate the seasons and extreme weather events. Of course as with any new technology there will be unexpected side effects and there is no guarantee they will work. So you probably don't want to be the first on your block to try new materials.
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