After two years of operation, my house has demonstrated better than net-zero source energy operation, with detailed data provided at http://www.residentialenergylaboratory.com/net_energy_use.html and further links from there.  This was accomplished in a standard production, wood-frame house modified during the design phase with the following: (1) upgraded insulation package for ceiling (R-60), walls (R-27), and crawl space (R-19 walls, R-5 underneath), (2) redesigned roofs on house and garage to get overhangs on south side, and mounting place for solar systems, (3) upgraded to triple-pane windows with high solar gain on three sides of the house, (4) addition of one window on south side, (5) addition of a modest size 3.15 kW DC photovoltaic (PV) system, (6) addition of a small solar thermal system for domestic hot water, and (7) addition of interior cellular shades on windows.

Total additional cost for these modifications was $22,080, excluding windows but including the cost for the high solar gain coatings.  Including the cost for upgrading the windows from double-pane vinyl to triple-pane wood/aluminum cladding, which was cosmetic as well as for energy savings, the total cost for all modifications was $28,580.  This was less than the cost for upgrading the lot size and the granite!

Thus, it is possible, with a quality builder, to achieve a very low-energy, or even net-zero source energy home by straightforward changes in the design phase of home construction.  It is much less expensive to make these changes during the design phase than after a house is built.  If working to stay within a budget, it is necessary to compute energy savings and costs for each proposed modification.  You can see the cost/benefit analysis for this project at http://www.residentialenergylaboratory.com/costs.html.  (Caveat:  Achieving net-zero source energy is easier here than in many parts of the U.S. due to the high solar insolation here, but the winters are significant at this location, a Colorado mountain valley that averages over 7000 deg F (3900 deg C) heating degree days annually.)

What type of insulation did you use?

Posted By NFC on 17 Jul 2012 12:41 PM
What type of insulation did you use?

Under the crawl space, 1" XPS (extruded polystyrene) rigid foam was used.  For the inside of crawl space walls, fiberglass with a perforated facing was used.  The rim joist was sprayed on the inside with about 1.5" closed cell foam, and then covered with 6" of unfaced fiberglass.  The outside of the rim joist was covered with 2" of XPS rigid foam.  The 2"x6" walls were sheathed with OSB and caulked around all junctions with the 2x6's, and filled with wet sprayed cellulose, and the outside of the walls was covered with 2" XPS.  Fiber-cement (HardiPlank) siding was used over the XPS, and of course, sheetrock on the inside.  The ceiling was insulated with loose cellulose.  All penetrations were sealed with expanding foam.  Infiltration reduction boxes were used around all electrical boxes on external walls.  More construction details and lots of pictures are at http://www.residentialenergylaborat...ption.html.     

This is a very dry and low humidity climate with well-drained soils, and some of these insulation choices (like fiberglass on the crawl space walls), which were mostly made by the builder, should be different in a wetter climate.