The stated goal of this project was to reach a "reasonably affordable" end product. Any strategy that adds more than 10% to the construction cost, or with a payback period longer than the mortgage, would, for an end user on a budget, become cost prohibitive. They are no longer an investment, but a luxury.
The goals set for "reasonably affordable" were very straight forward: 1. Employ strategies that do not add more than 5% to the construction budget, and 2. Employ strategies that have a payback period of 10 to 15 years. Under current market conditions, this adds about $5-$7 per square foot to the cost of construction, the targeted maximum.
There's an old saying about an ounce of prevention being worth a pound of cure. In this case, its an ounce of conservation. Since the building envelope was targeted as the most immediate factor in reducing energy use, that's where the first cost analyses went. The SIP panels were, surprisingly, not as expensive as initially thought and in fact priced out very close to a stud wall with an equivalent R-value construction (6" SIP @ R-24 vs staggered stud wall w/ urethane and batt @ R-24) . They did, however, have a trickle down effect on pricing for other systems. The air tightness of the construction necessitated a Heat Recovery Ventilator (HRV) to keep the air fresh (though a tightly constructed house would need one anyway, SIPs or no SIPs) and the electricians wanted to charge more for working with the panels. Careful attention to electrical outlet and switch placement to minimize interaction with the SIP walls convinced the electrician not to charge more, however, and the framing crew also drilled the splines to match the factory chases when possible during construction. Choosing the 8" panel required larger window and door jambs, which did add some to those costs as well. The biggest factor to controlling SIP costs was planning. Coordinating windows, doors, structural members and electrical runs as completely as possible saved on in-field modifications to the panels. The remainder of the building envelope was of standard construction with extra insulation, and used urethane and acoustical sealant to tighten everything up. The extra cost in the insulation only amounted to a 0.5% cost increase, probably the best value in the envelope.
The window package was the next item evaluated. Two different high performance (triple pane) window systems were investigated, but ultimately proved too pricey to make the cut. Because the rest of the building envelope was already over-insulated and air sealed, the windows added minimum benefit: estimated at a 4% increase in energy efficiency. This equated to a payback period far exceeding the initial restriction of 10 to 15 years, and went even beyond the 30 year mortgage. Ultimately, the window package selected was chosen as much for its use of sustainable forestry, efficient manufacture and high quality construction as for its energy performance. This decision resulted in a window package that was the same cost as most other aluminum clad window systems. A vinyl window system would have performed as well at even greater cost savings.
The third largest single cost increase was in the forced air heating system. It should be noted, however, that this cost increase was compared to the most basic, minimally efficient system that could be implemented. Most systems would be closer in cost to the one chosen, especially if they incorporated more than one zone. It should also be noted that the forced air system came in about $6000 cheaper than a radiant heat system. (Take a look at the Strategies pages to see why forced air was chosen). The Carrier Infinity system, which offered an incredibly efficient furnace bundled with a controller that went well beyond a typical programmable thermostat was the winner. In HVAC systems, continual feedback from the environment can allow the system to adjust more often and keep things running at optimal efficiency. The system was also split into 2 zones, one upstairs and one downstairs. Zoning the systems adds to the cost, but makes a huge difference in keeping the house comfortable and running more efficiently. The HRV was also provided by Carrier and controlled by the same system. This allowed the control and integration of the various pieces to be as seamless and straightforward as possible. The Infinity control system also provides status monitoring for air filters and other equipment maintenance, making the system easier to maintain.
Other costs associated with reaching LEED and Energy Star, as well as a breakout of specific costs by product.
Where the tradeoffs were made to keep costs within 5% of construction.
How it might have been done for less!