Passive Survivability

When oil platforms blow up, volcanic ash is blown across a continent, or when earthquakes tremors shake a bit too close to home, my thoughts turn to passive survivability. This term is generally used to describe a building's ability to maintain critical life-support conditions in the event of extended loss of power, heating fuel, or water. I.e., how long could you live off the grid?

Passive survivability adds a self-preservation motive to the existing strong economic incentive of energy efficient construction. But is also calls for measures such as istern water storage, electric vehicle battery back-up to solar panels, and alternate sources of heating, like a wood stove. Not surprisingly, this harkens back to vernacular design, which was more disaster tolerant by matter of definition. We relearn to use windows for daylighting, harnessing the sun’s warmth and the wind’s coolth.

A key component of this survivability is the ability of the structure to survive when set upon by the wrath of man or nature: fires, wind events, driving rains and freezing temperatures. We typically think of vulnerability to Hurricane Katrina & her many cousins, but it is the army of mold and mildew following such events which really destroy a structure. In warm weather disasters, the penetration of the outside shell is followed by an intrusion of moisture which can quickly render the building uninhabitable. In the wintry north, this may occur when heated indoor air escapes up to the snow-covered roof and catalyzes a series of thaw, freeze, backup under roof shingles, drip into the house, rot, mold. Same story, just the cold weather version.

What to do? "High insulation and high mass with some passive solar gain and summer shading will dramatically improve survivability,” says John Straub, Ph.D., an engineer and building science expert at the University of Waterloo in Ontario. The mass prevents penetrations from air-born missiles in high wind events in the worst of times, and provides temperature moderation at all other times. The best part about mass (concrete, brick) is that if it gets wet, it will dry out and NOT mold. If the insulation is equally not moisture sensitive (ie EPS, or NEOPOR), and is continuous from wall to ceiling, then at least one is assured that the building envelope will continue to function as designed, both structurally and thermally.

You can sleep on that.