In the 2001 testing, Cell #2 with the double roof/sealed attic showed the lowest attic temperatures and narrowest temperature range. (Please see Table 27, and Figures 71, and 73.)   Peak attic temperatures in Cell #2 were 5^oF to 6^oF lower than this same sealed cell the year before, without the double roof.  This indicates that the double roof did provide a substantial benefit.  Since there is no insulation on the attic floor though, there still is a significant heat gain across the ceiling.  In fact, the ceiling heat fluctuation actually is higher than the reference Cell #5.  (Please see Figure 72.)

The true impact of the double roof construction of Cell #2 is most likely a combination of the benefits of a cooler attic space that reduces duct heat gain and minimizes the effects of air leakage from the attic into the house, and the drawback of the higher ceiling heat flux.

Cell #3 with its spectrally selective dark brown metal shingles, produced lower attic temperatures at night, but higher roof deck temperatures (which were most likely due to the insulating quality of the shingles which have an air space underneath them).

Figure 71.  2001 Experimental roof cell.  Cell #1 is located on the left, and Cell #6 on the far right.

Figure 72.  2001 heat flux measurements across attic.

 

Figure 73.  2001 mid-attic temperatures.

Habitat Homes - Fort Myers, Florida:  In July 2000, FSEC and Florida Power and Light instrumented six side-by-side Habitat for Humanity homes in Ft. Myers with identical floor plans, orientation ,and ceiling insulation, but with different roofing systems.  A seventh monitored house contained an unvented attic with insulation on the underside of the roof deck rather than on the ceiling.

An evaluation of roof and attic thermal performance clearly showed the energy-saving benefits of reflective roofing systems in Florida.  Tested roofs with high solar reflectance offered impressive air conditioning energy savings, especially the tile and metal roofs with a solar reflectance between 65% and 75%. (Please see  Table 28.)

(RGS) Standard dark shingles (control)	(RTB)  Terra cotta S-tile roof
(RWS) Light colored shingles	(RWB) White "barrel" S-tile roof
(RSL) Standard dark shingles with sealed	(RWF) White flat tile roof
attic & R-19 roof deck insulation	(RWM) White metal roof

Site	Total kWh	Savings kWh	Saved Percent	Demand kW	Savings kW	Saved Percent
RGS	17.03	----	----	1.63	----	----
RWS	15.29	1.74	10.2%	1.44	0.19	11.80%
RSL	14.73	2.30	13.05%	1.63	0.01	0.30%
RTB	16.02	1.01	5.9%	1.57	0.06	3.70%
RWB	13.32	3.71	21.8%	1.07	0.56	34.20%
RWF	13.20	3.83	22.5%	1.02	0.61	37.50%
RWM	12.03	5.00	29.4%	0.98	0.65	39.70%

Significant findings:  Reflective roofing materials represent one of the most significant energy-saving options available to homeowners and builders.  These materials also reduce cooling demand during utility coincident peak periods, and are potentially one of the most effective methods for controlling demand.