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Route 4 near Killington, Vermont was closed for more than a month due to flooding from Tropical Storm Irene. Photo: Lars Gange and Mansfield Heliflight. Click on image to enlarge.

Anyone who was in Vermont in late August of this year and witnessed the raging floodwaters from Hurricane Irene and the havoc they wreaked, gained an intimate view of the vulnerabilities we face from intense storms and flooding. Hundreds of miles of roadway were heavily damaged, dozens of bridges washed away, and some communities were cut off for weeks. Vermont is not alone. Throughout the Northeast, there was a 67% increase in heavy rainfall events (defined as the heaviest 1% of all rainfall events) from 1958 to 2007, according to the multi-agency U.S. Global Change Research Program.

Climate scientists tell us to get used to it.

As the planet warms over the coming decades, precipitation will increase overall--due to greater evaporation from bodies of water and, thus, more water vapor in the atmosphere--though there will be significant regional variation. Even in areas that see a drop in precipitation (an expected trend in much of the western U.S., for example), the rain that does fall is expected to increasingly fall in deluges. So, we need to prepare for more Hurricane Irenes and the resultant flooding. Along with more intense rainfall events, we can expect stronger winds. Some of these winds will be from tropical storms whose intensity is magnified as their air masses pass over a warmer South Atlantic and Gulf of Mexico. Others of the winds will be more localized thunderstorms that result from air masses over land warming and rising into intense cumulonimbus clouds.

In coastal areas, sea level rise will play into this, as coastal storms increasingly cause storm surges--the situation that befell New Orleans in 2005 with Hurricane Katrina. Even a few inches of sea level rise dramatically increases vulnerability to storm surges. How quickly sea levels will rise depends on the ice mass on Greenland, and scientists are far more worried about this than they were just a few short years ago.

Resilient design

The bottom line is that we need to change the way we build our houses and design our communities to protect us from such storms. This is an important part of resilient design--which is the subject of this and the series of blogs that will follow.

There are a lot of strategies that come into play with storm-resistant construction. A few of these are described below:

Building to stringent hurricane standards

In designing homes that will hold up well in strong winds, we should borrow heavily from he Miami-Dade County Building Code, which includes a wide range of provisions, including hurricane tie-down strapping or clips that provide a continuous structural connection from foundation slab to roof, minimum 2x6 framing in exterior walls, minimum 19/32-inch plywood roof sheathing with 6-inch nail spacing at panel edges and 4-inch at gable ends, and hurricane-rated shingles. Other wind-resistant strategies include hip roofs that deflect winds, avoidance of deeply overhung entryways, and outward-opening doors that are held more tightly closed in heavy wind.

Hurricane strapping and components for providing a continuous structural connection between foundation and roof. Photos: Simpson StrongTie. Click on image to enlarge.

Note that some measures for ensuring structural integrity in intense wind events conflict with strategies to improve energy performance or reduce resource use. The Miami-Dade County Hurricane Code, for example, calls for 16-inch on-center 2x6 exterior wall framing, double top plates, and corners comprised of a minimum of three studs--measures in direct opposition to advanced framing.

Control of wind-driven rain

Adequate overhangs are key to keeping rain away from homes. I like at least 24-inch-deep overhangs, in some cases even more. Gutters are advisable to capture rainwater, with downspouts and horizontal lines to carry collected water away from the house.

Basement drainage should include continuous perimeter drains that extend to the bottom of the footings. Foundation walls or the slab edge (with slab-on-grade construction) should be coated with a dampproofing layer, covered with a foundation drainage board, and backfilled with free-draining crushed stone. The perimeter drains should drain to daylight if topography permits. And the ground surface should slope away from the house.

Walls should be designed with rainscreen detailing that allows trapped moisture to escape and provides a pressure break for wind-driven rain, while allowing any moisture that does penetrate the siding to drain to the base of the wall or evaporate and escape. With an adequate overhang, the siding won't even get wet with most storms.

Control of stormwater

More intense rainfall events will mean greater volumes of runoff, or stormwater flow. This means we should be installing larger-diameter storm sewers and culverts. It also means that we need to do everything we can to provide for infiltration of rainwater where it falls--so that we don't need to transport that water at all.

Getting ready to pour a concrete ceiling on a modular safe room in Sioux City, Iowa. Photo: Dave Gatley, FEMA. Click on image to enlarge.

The latter can be accomplished by minimizing impermeable surfaces, providing infiltration trenches (filled with crushed stone) between adjacent impermeable surfaces such as sidewalk and driveway, installing permeable pavement, avoiding curbs along driveways and roads, and providing grassy swales and infiltration basins that allow runoff to spread out and soak into the ground.

Along any waterways, we need to consider erosion risk. As we saw so clearly with Tropical Storm Irene in Vermont, intense rainfall events--particularly if the ground starts out nearly saturated--can result in streams and rivers quickly overflowing their banks. We need to provide for this in our placement of homes and outbuildings. The right plantings can help to stabilize banks and resist erosion.

Safe rooms

In parts of the country where tornadoes and hurricanes are most common, we should consider installing safe rooms to provide a safe haven in an extreme wind event. These are small bunkers in our homes or garages, anchored to concrete slabs and typically built of reinforced masonry block with steel-beam roofs. Such rooms are typically not connected to the walls of the house, and they should be equipped with battery-powered or wind-up radios, flashlights, etc. Excellent information on safe room design and construction is available from FEMA.

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In this resilient design series, I'm covering how to improve the resilience of our homes and communities, including strategies that help us function well in the aftermath of a major storm or event that results in lost power, interruptions in heating fuel, or water shortages. We'll see that resilient design is a life-safety issue that is critical for the security and wellbeing of families in a future of climate uncertainty and ever-present risk of terrorism.

Alex is founder of BuildingGreen, Inc. and executive editor of Environmental Building News. To keep up with his latest articles and musings, you can sign up for his Twitter feed.

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Comments

1 A Contrarian View posted by Robert Riversong on 11/09/2012 at 10:33 am

The paradigm of civilization, from it's beginnings with large-scale hydraulic agriculture, has been to wage a war with nature's implacable forces in order to dominate, exploit, expand and thrive. In evolutionary history, violent weather, predation and disease helped keep the human population in check. But now we fend off death with every tool and method our minds can muster.

The Cherokee once burned their clothes every year as a literal "house-cleaning" to avoid accumulating unnecessary stuff, and may have periodically burned down their homes as well. Durability was not an issue when new homes and clothing could be easily created from local renewable resources.  Today, our ecological impacts are so high, that durability means everything must last nearly forever, just as we struggle to postpone bodily death for as long as possible using extreme and expensive medical procedures and toxic drugs.

We do battle with nature with flood-control dams, such as on the Mississippi River, which often shfit the flooding elsewhere and sometimes make it worse. There is talk now about walling off New York City from the ocean's fury. We don't know what the unintended consequences might be.

Is the path to resilience through bunkers and "safe rooms", or is it through re-learning to live in harmony with nature and welcome death when it comes? The Lakota were famous for waking up with the notion that "It's a good day to die". How far are we willing to go to fend off the death and decay that are inevitable elements of nature's cycle? Do we lose the battle by spending so much effort in trying to win?

 


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