Equation NA6-1
UT= C1 + (C2 X Uc)
Where:
UT = U-factor Is the Total Performance of the fenestration including glass and frame
C1 = Coefficient selected from Table NA6-6
C2 = Coefficient selected from Table NA6-6
UC = Center of glass U-factor calculated in accordance with NFRC 100 Section 4.5.3.1 http://www.nfrc.org/software.aspx
| Product Type | Frame Type | C1 | C2 | 
| Metal | 0.311 | 0.872 | |
| Metal Thermal Break | 0.202 | 0.867 | |
| Non-Metal | 0.202 | 0.867 | |
| Skylights with a Curb | Metal | 0.711 | 1.065 | 
| Metal Thermal Break | 0.437 | 1.229 | |
| Non-Metal | 0.437 | 1.229 | |
| Skylights with no Curb (Deck Mounted) | Metal | 0.310 | 0.878 | 
| Metal Thermal Break | 0.195 | 0.882 | |
| Non-Metal | 0.310 | 0.878 |