Reflective Insulation

Summarize, insulating the envelope of a building’s conditioned space yields these key benefits:

1.   Provides a much more comfortable, productive and livable structure. In addition, the effects of moisture condensation and air movement are minimized in well-insulated buildings. This results in lower maintenance costs and increased longevity of the building structure.

2.   Reduces energy requirements, which lowers utility bills.

3.  Supports economic, environmental and energy conservation goals. This is evidenced by the numerous studies sponsored by the Department of Energy.

Heat moves through wall cavities or between roofs and attic floors by radiation, conduction, and convection. In some buildings, radiation is the dominant method of heat transfer. A reflective insulation is an effective barrier against radiant heat transfer because it reflects almost all of the infrared radiation striking its surface and emits very little of the heat conducted through it. By virtue of its impermeable surface, reflective insulation also reduces convective heat transfer. Mass insulation like fiberglass or foam board primarily slows conductive heat transfer, and to a smaller extent, convective heat transfer. However, mass insulation is not as effective against infrared radiation, actually absorbing it rather than reflecting or blocking it.

According to CCHRC, Reflective insulations are designed to reduce radioactive heat transfer by placement of one or more reflective surfaces in combination with an air gap.  The reflective surface reflects most of the thermal radiation toward the air space, preventing it from being transmitted or absorbed by the material. The air gap ensures that there is little or no heat transfer by conduction in that space, which would be the dominant heat transfer mechanism if the air gap was filled.  A familiar application of reflective surfaces is in the attics of homes in warm climates, where reducing the radioactive heat transfer from hot roof decking to the underlying attic insulation lessens air conditioner loads. Despite the effectiveness of reflective surfaces in this context, it has not been demonstrated that radioactive heat transfer from homes in cold climates is significant enough to merit use of reflective insulation. Furthermore, reflective insulation can affect water vapor transmission because they are commonly strong vapor retarders and can induce condensation by reducing surface temperatures (ASHRAE, 2009).

Therefore the use of reflective insulation requires consideration beyond the need for thermal insulation.

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