Plains Habitat

Structural Insulated Panel Field Project

Most of Habitat's 1400+ American affiliates build wood frame houses. However, some affiliates are experimenting with other systems including straw bale construction, ICFs, and SIPs. Sumter County Habitat for Humanity, the original affiliate started by Habitat founder Millard Fuller, partnered with the Department of Energy and the Structural Insulated Panel Association (SIPA) to build two SIP houses in Plains, Georgia. This field project seeks validation of heating energy savings from SIPs.

Figure 1. Energy Use in this Sumpter County Habitat Home, Built with Conventional
2x4 Framing in Plains, GA, was Compared to SIP Constructions

The affiliate built the two SIP houses and a frame house on three neighboring lots. The Structural Insulated Panel Association (SIPA) provided some assistance with the SIP houses. The three houses were intentionally built with their calculated energy performance (HERS score) similar to each other as seen in Table 1 . The frame house (Figure 1) featured energy related details typical for the affiliate which resulted in an ACH50 of 5.3. With the home's whole-house fan cover installed the ACH dropped to 3.9, very good for frame construction. However, testing results revealed much better performance in the SIP (Figure 43) houses with a measured ACH50 of 1.8. Though this indicates a 50% decrease in infiltration, that does not correlate directly into a 50% heating energy savings since infiltration determines only a portion of the total heating energy use. Other factors include insulation levels, conditioned square footage, window area, number of occupants, occupancy patterns, use of supplemental heaters, heater operation strategy, and indoor temperature. Monitoring equipment was installed to measure total, heating, and water heating energy use, as well as indoor and outdoor temperature (Table 1).

House	Structural System	ACH50	Average Hourly Indoor T (F)	Condit. Floor Area (sq. ft.)	HERS Score
1	SIP	1.8	75	1036	82.7
2	SIP	1.8	75	1069	83
3	Frame	5.3	80	1208	82.9

Table 1. Sumpter County Habitat for Humanity Field Study

A 1995 study of 10 Habitat homes in Florida City, Florida revealed that the maintained indoor air temperature heavily influences conditioning energy use (Parker, et al. 1995). Preliminary analysis suggests that this may be a significant factor in the Sumter County study. The three houses' indoor average hourly temperatures and the outdoor average hourly temperature for December 1998 and January 1999 are illustrated in Figure 2. Note that the frame house (green) consistently maintained a higher indoor temperature than the SIP houses (red and blue). The impact of this considerable difference (average of 5F) is accounted for in Figure 3 showing heating energy use (per 1,000 ft2 of conditioned space) as it relates to the indoor-outdoor temperature difference. Though savings vary from day to day based on weather, considering the average indoor-outdoor temperature difference of 30oF, the SIP houses saved 25% compared to the frame house.

A previous study conducted in Louisville, Kentucky comparing SIP to frame construction found a 15% savings for the SIP construction (Rudd, 1997). In that study, the duct systems for both houses were located in conditioned spaces. The Plains SIP houses had ducts in the conditioned space while the frame house had ducts in the unconditioned attic. The 10% difference in the Plains and the Louisville findings are attributed to the differences in duct system locations. Together, these two studies suggests that homes of 1,200 ft2 and smaller stand to gain significant energy performance from SIP construction with heating energy savings of 15-25% depending on duct location and average indoor-outdoor temperature differences.