superinsulation

EHH week 17: resilient design

Most houses are totally dependent on municipal utilities for power and water, what a friend of mine calls “life support.”  Cut the utilities, and the occupants are left to freeze in the dark while their food rots. 

 

A major goal for Harvest House’s owners is to be able to withstand all nature’s calamities in their house.  In the Seattle area these include earthquakes, floods, and wind.  In December 2006, a wind storm left over 1 million without power, some for as long as 5 days. 

 

This house was designed by the structural engineer, Harriott Smith Valentine, to the strength of a critical facility, like a hospital or an airport control tower.  The building is superinsulated, has a root cellar to store food, and has four huge tanks in the basement to store rainwater.  Without any operating equipment, the occupants will have shelter, warmth, food, and water. 

 

Factor in its solar energy systems, and this house can enable its occupants to live in complete comfort for at least 3 weeks.  With both photovoltaic (solar electric) panels and solar hot water tubes, which are backed up by batteries and a propane generator, the lights will glow, the refrigerator will stay cold, the oven can warm, the heat will flow, and the water will be potable.  By rationing their usage of electricity, they could live independently for many months.

 

With climate change ratcheting up the frequency and intensity of storms and droughts, there is a growing interest in what Alex Wilson calls Resilient Homes.  Alex and Jerelyn Wilson of Building Green visited Eastside Harvest House in October 2011.

EHH week 11: roof venting

The roof of this house is one large plane tipped up to the western view.  This shape allows us to stay under the 25 foot height limit (not easy to do with a two story house) and simplifies rainwater collection because everything flows towards one side of the house.

 

Because we are superinsulating, we are using the full depth of the roof joists for blown-in insulation.  Well, all except the upper 1-1/2 inches which must remain void to ventilate the roof.  This 1-1/2 inches allows air to carry away any vapor that condenses into water on the underside of the sheathing.  Without the ventilation space, the roof structure would rot.

 

The ventilation space must run continuously from the eave at the low end to the eave at the high end in every single joist bay.  I like to think of an ant crawling on the underside of the plywood from one edge of the roof to the other. 

 

Trouble is, seismic design wants to have the roof sheathing fully nailed at its perimeter to the tops of the exterior walls.  On this house, we solved the issue with semicircular holes in the perimeter blocking that allow nails between the holes.  At the rakes (the sloping sides of the roof) we had to lower the required cross blocking to avoid blocking the air passage.  And at the one part of the roof that is overframed, we drilled over 100 holes through the lower sheathing to let air pass up and out.