Everything I read about reflective barrier suggest placing the barrier on the attic side of roof rafters however, I live in Ohio, and I see reflective barrier put on top of insulation on the floor of the attic. Does this offer any benefit in the attic during winter? Does the barrier help to keep insulation cool in summer thereby causing less heat gain to the living space? Is there an equation that reflective barrier makes up for some insulation, so less R-Value is needed in attic?
Answer:
Often it isn’t possible to place the radiant barrier in the preferred and recommended position — attached to the roof rafters. Sometimes because the roof pitch is too shallow to physically get to it or there is too much mass insulation on the floor preventing working on top of it. In those cases, the radiant barrier can be placed on top of the floor insulation — making sure the radiant barrier is perforated to allow moisture to escape. Sometimes installers will install it there just because it’s easier to do, and as long as the top side of the radiant barrier remains clean and relatively free of dust, it will perform very well. In most climates it will give benefits both during hot and cold weather cycles. Winter performance of radiant barriers are not nearly as good as summer times; and if you live in an area of many winter sun days, there might be a slight reduction of performance because one wouldn’t benefit from the extra sun heat in winter months.
Radiant barriers do not add R-Values to the thermal performance equation — they just reduce the amount of heat that enters the attic space thereby making the existing mass insulation have less heat to resist.