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First of all, where the R-value is used to rate the energy efficiency of a single component - a batt of insulation for example - U-values rate the energy efficiency of the combined materials in a building component or section.
When installing a batt of insulation, the vapor barrier - that's the paper or foil face - needs to face toward the heated space.
Use a straight edge to assure a good straight cut across the fiberglass batt .
Care must be taken in removing the water so that the batt isn't stretched or torn.
No batt insulation would be required in this case.
Other
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