Is it possible to create a net zero energy building by renovating an existing home? Yes! This 2,400 square foot house was built in the 1970s. With a desire to live sustainably, the homeowners decided to set an energy budget of 10 kWh/day for their home. A budget of $100,000 was set for the renovation. The budget was very roughly 1/3 for solar photovoltaics (PV) and solar hot water, 1/3 for energy-related changes such as the metal roof and new appliances, and 1/3 for other changes including the addition of a master bath, replacement of carpet with hardwood and tile, and removal of a retaining wall.
In the first year of full-time occupancy by one person the house generated over 1,500 kwh more power than it used. So with one occupant, the home was actually better than net zero energy, it generated more power than it consumed. Beginning in July 2007, three additional family members moved into the house. As of July 2008, some of the accumulated credit had been used up, but overall the home has still generated more energy than it has used.
Changes to this home continued through 2009. These changes include:
- Removing all fiber insulation from attic as preparation for foam insulation
- Adding 1×3 furring strips in attic from the soffit to the ridge vent and tacking lauan to the furring strips. This creates an air gap from the soffit to the ridge vent for foam application
- Adding 4 inches of foam on lauan, 3 inches of foam on gables, and 1 inches of foam flashing on ceiling (scheduled for end of September)
- Adding a whole-house fan
- Replacing the old 4 ton Seer 10 heat pump with a 2 ton SEER 18 unit, (mainly for humidity control)
- Caulking and foaming air leaks reduced air infiltration from 2300 cf/min to 1700 cf/min at 50 pascals
- Tilting PV panels to allow for more ventilation and better winter power production
- Tilting the solar thermal panels to 50 degrees for a winter bias, and adding more collection and storage