Assess the cost-effectiveness of a roof retrofit using a SIS for a Golden, CO, house that has an overall BLC of 400 W/°C and roof insulated with RSI-5.9 with an exposed area of 180 m². Estimate the potential annual electricity use and cost savings due to the SIS-roof operated with two-step controls with a low R-value of RSI-0.7 and a high R-value of RSI-5.9. The house equipped with a heat pump provides both heating (COP_H = 2.8) and cooling (COP_C = 4.2). The SIS-roof is estimated at $40/m² and the electricity price is $0.12/kWh. Perform the cost analysis using the LCC approach with a discount rate of 5 percent and a lifetime of 30 years.