(1) (a) The following design parameters shall be used for calculations required under this section. Computations submitted by a licensed architect or engineer, contractors, builders, and owners shall be considered as acceptable when calculated by acceptable engineering procedures. Values for table 1 are to be selected from standard RS21 of the Colorado energy conservation standards (design temperatures for Colorado cities and towns, supplement to climate data for air conditioning design, ASHRAE Rocky Mountain region, April, 1978).

Table 1

Location _____________________________

Winter design dry-bulb degree_________ F

Degree days heating __________________

(b) Minimum thermal performance standards for residential buildings on which construction commences on or after November 1, 1979, shall conform to one of the alternatives provided in subsections (2), (3), and (4) of this section. Renovation that commences on or after November 1, 1979, shall conform to one of the alternatives provided in subsections (2), (3), and (4) of this section, or renovation standards promulgated by the board for energy efficient building standards.

(2) (a) Any separate envelope component of a residential building that is heated shall not exceed the combined thermal transmittance value (U0) derived from equation 1 using values in table 2. Values for the purposes of table 2 shall be determined by using the graphs (figures 1, 2, and 5) contained in the Colorado energy conservation standards. The combined thermal transmittance (Ur) for roofs or ceilings shall not exceed 0.05 BTU/H FTsuperior 2 degree F for geographic areas with eight thousand or less Fahrenheit heating degree days and shall not exceed 0.04 BTU/H FTsuperior 2 degree F for geographic areas with more than eight thousand Fahrenheit heating degree days. Roof or ceiling assemblies in which the finished interior surface is the underside of the roof deck may have a maximum Ur value of 0.08 BTU/H FTsuperior 2 degree F. Equation 1 shall be used to determine acceptable combinations to meet the required U0 values.

Table 2

(b) If all exposed concrete walls average less than two feet above grade, those walls are exempt from the calculations for Uw and insulation.

(c) Heating equipment shall be sized using climate data from table 1 in subsection (1) of this section.

(3) (a) If any segment (wall, floor, roof) of the exterior envelope does not comply with the standards prescribed in subsection (2) of this section, the thermal transmittance value (U0) of any other segment (wall, floor, roof) may be decreased so that the resulting thermal transmittance value (U0) of the envelope complies as if the building had been designed in compliance with subsection (2) of this section. For this purpose, reduction of the thermal transmittance value of any of the other exterior components of the envelopes may be used to achieve compliance.

Equation 1

(b) Use of the equation provided in paragraph (a) of this subsection (3) requires two sets of calculations. The first calculation utilizes the U0 values obtained from subsection (2) of this section and the actual areas of the proposed residential design. The second calculation utilizes the actual U0 values and the actual areas of the proposed residential design.

(4) Computations submitted indicating that the total fossil fuel energy required in a residential building, through design or otherwise, equals or is less than the total fossil fuel energy used if the dwelling is built or renovated according to standards contained in subsections (1) and (2) of this section shall be considered an acceptable alternative. The total fossil fuel energy required shall be computed as the annual estimated BTUs necessary for the proposed residential building.

(5) Repealed.