Example Calculation Using the TIMA Formula

Assume a metal building roof structure with the following characteristics:

Length of Building Section = 100 feet

Number of Purlins = 21 purlins

Fastener Population per Foot of Purlin = 1 per foot hr-ft2°F

Insulation thickness = 5 inches is in the flexibility of the facing itself. The improvement in permeability rating produces a higher U-factor rating due to the draping characteristics. During installation, the insulation is pulled tightly from eave to eave of the building. The flexibility of vinyl facing allows it to stretch and drape more fully at the purlins than reinforced facing. Figures 9.15 and 9.16 show a generalized illustration of the difference in drape of the vapor retarders and the effect on effective insulation thickness.

The thermal bridging and insulation compression issues discussed above make the following recommendations worth considering.

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