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R-VALUE, WHAT IS IT?

R-value is the measure of thermal resistance. It is a measure of how well an object, per unit of its exposed area, resists conductive heat flow; Materials such as reflective foil have high reflectivity and would work great in reflecting heat, but would function poorly as a conductive insulator. The greater the R-value, the greater the resistance and better the insulation works against heat absorption (mostly, conductive heat). The R-value (thermal resistance per unit area) depends on the type of insulation, its thickness, its quality, and its density. According to current standards, R-values are most reliably stated for bulk insulation materials.

CAUSES OF DETERIORATION OF R- VALUE

AGING: Age will wear out the insulating materials and reduce their efficiency. Foam insulation degrade over time in terms of R-value; they mostly comprise of gases such as chlorofluorocarbons (CFC) or hydro chlorofluorocarbons (HFCs) which, in time, are replaced by air molecules. This causes them to lose their efficiency as insulators.

INFILTRATION:  Air infiltration can allow convective heat transfer or condensation formation, both of which may degrade the performance of the insulation. The insulation’s efficiency and its R-value would be degraded considerably by this continuous infiltration. Presence of moisture also downgrades the R-value, so it is very important to prevent moisture from entering the insulation system.

RIGIDITY: Rigid insulation can shrink and dry over time. This leads to gaps in coverage, reducing the effective R-value. Some rigid boards (such as polyisocyanurate) and spray polyurethane foams lose R-value as the blowing agent leaks out over several months, or possibly years. Rigid insulation are generally impervious to water damage but can suffer degradation if left exposed to sunlight (heat) and erosion.