Ted is a software engineer and all-around geek who has long wanted to build a house from scratch. Andrea is his loyal wife who considers assembling IKEA shelves the apex of her DIY career. A website designer by trade, she is slowly turning into an armchair expert on green building. Can these two crazy tree-huggers succeed in building an outrageously energy-efficient house together, and will they still get along when it's all finished?
What's an "almost passive" house? Passive houses are a relatively new style of building pioneered in Europe — they are way more energy efficient than most houses built today. Here's an overview of the approach (adapted from Homes for a Changing Climate):
- Eliminate thermal bridges: Thermal bridges are the path of least resistance for heat to flow out from a house. They occur when an element in the house has higher heat conductivity than the surrounding materials. For example, a balcony slab that isn't thermally isolated from an interior concrete floor can suck the heat right out of the house.
- Make it airtight: This is done partly by wrapping an intact, continuous layer of airtight materials around the entire building envelope.
- Promote indoor air quality with mechanical ventilation: Because passive houses don't "breathe" the way a normal leaky house does, an energy recovery ventilator (ERV) is used to exchange indoor and outdoor air. Heat loss is often minimized by passing the air through an "earth tube," which is roughly 130 feet (40m) of 8-inch tubing buried 5 feet underground (this minimizes cold-air loss during summer as well).
- Use high-performance windows and doors: Triple-paned, low-E, etc.
- Use passive-solar principles when designing and orienting the house.
The Passivhaus standard is extremely strict and we don't yet know for sure if we'll be able to meet it, so we're claiming only to build an Almost Passive House. But whether we get Passivhaus certification or not, we still expect it to use roughly 80% less energy for heating and cooling than a conventional house. Trickle-down green building Thousands of Passive Houses (Passivhäuser?) have been built in Europe, but so far only a few dozen have been built in North America. A big part of our goal in building this way is to spread the word about this kind of construction, both online and locally. Any or all of the Passivhaus techniques can be applied to any new construction or remodel, so we hope our house and blog will trickle down into comfier, more efficient houses everywhere.