REFLECTIVE INSULATION

Definition: Thermal insulation consisting of one or more low emittance surfaces, bounding one or more enclosed air spaces.

• 6.1 Concept of Reflective Insulation
  • Standard types of insulation, such as fiberglass, foam, and cellulose primarily reduce heat transfer by trapping air or some type of a gas. Thus, these products or technologies reduce convection as a primary method of reducing heat transfer. They are not as effective in reducing radiant heat transfer, which is often a primary mode of heat transfer in a building envelope, in fact, these products, like most building materials, have very high radiant transfer rates. In other words the surfaces of standard types of insulation are good radiators of heat.
  • Reflective insulation uses layers of aluminum, paper, and/or plastic to trap air and thus reduce convective heat transfer. The aluminum component however is very effective in reducing radiant heat transfer. In fact, the metalized and foil materials commonly used in reflective insulation will reduce radiant heat transfer by as much as 97%.
  • Heat flow by radiation has been brought to the public’s attention with high efficiency windows, which commonly use the term “Low E” to advertise the higher performance ratings. The “E” stands for emittance and the values range from 0 to 1, with 0 being no radiation and 1 is the highest measure of emittance or radiation. Most building materials, including fiberglass, foam and cellulose have surface emittances or “E” values in excess of 0.70. Reflective insulations typically have “E” values of 0.03 (again, the lower the better).
  • Therefore, reflective insulation is superior to other types of insulating materials in reducing radiant heat. The term reflective, in reflective insulation, is in some ways a misnomer, because aluminum either works by reflecting heat (reflectance of 0.97) or by not radiating heat (emittance of 0.03). Whether stated as reflectivity or emissivity, the performance (heat transfer) is the same.
  • When reflective insulation is installed in building cavities, it traps air (like other insulation materials) and therefore reduces heat flow by convection, thus addressing all three modes of heat transfer. In all cases, the reflective material must be adjacent to an air space. Aluminum, when sandwiched between two pieces of plywood for example, will conduct heat at a high rate.
• Reflective Insulation Manufacturers Association.
  • All insulation products including reflective insulation are measured by R-values, whereby the “R” means resistance to heat flow. The higher the R-value, the greater the insulating or thermal performance of the material.
  • Reflective insulation is a non-toxic, user and building owner safe, and environmentally safe building material.
  • In addition, the products are typically recyclable and thus can be termed a Green Building Material.
  • Another benefit is that the reflective insulation can also serve as a high performance and thus effective vapor barrier.
• 6.2 Understanding a Reflective Insulation System (RIS)
  • Layers of aluminum or a low emittance material and enclosed air spaces, which in turn provide highly reflective or low emittance cavities adjacent to a heated region, typically form a reflective insulation system.
  • Some reflective insulation systems also use other layers of materials such as paper or plastic to form additional enclosed air spaces.
  • The performance of the system is determined by the emittance of the material(s), the lower the better, and the size of the enclosed air spaces. The smaller the air space, the less heat will transfer by convection.
  • Therefore, to lessen heat flow by convection, a reflective insulation, with its multiple layers of aluminum and enclosed air space, is positioned in a building cavity (stud wall, furred-out masonry wall, floor joist, ceiling joist, etc.) to divide the larger cavity (3/4” furring, 2” x 4”, 2” x 6”, etc.) into smaller air spaces. These smaller trapped air spaces reduce convective heat flow.
• Reflective insulation differs from conventional mass insulation in the following:
  • Reflective insulation has very low emittance values “E-values” (typically 0.03 compared to 0.90 for most insulation) thus significantly reduces heat transfer by radiation
  • A reflective insulation does not have significant mass to absorb and retain heat
  • Reflective insulation has lower moisture transfer and absorption rates, in most cases
  • Reflective insulation traps air with layers of aluminum, paper and/or plastic as opposed to mass insulation which uses fibers of glass, particles of foam, or ground up paper
  • Reflective insulation does not irritate the skin, eyes, or throat and contain no substances which will out-gas
  • The change in thermal performance due to compaction or moisture absorption, a common concern with mass insulation, is not an issue with reflective insulation.
• Types of Reflective Insulation Materials
  • Reflective insulation has been used effectively for decades and is available throughout the world. The following are the major types of reflective insulation currently available:
    • Layer or layers of aluminum foil separated by a layer or layers of plastic bubbles or a foam material
    • Multiple layers of aluminum, kraft paper, and/or plastic with internal expanders an flanges at the edge for easy installation
    • Single layer of aluminum foil laminated to a kraft paper or plastic material when encapsulated with an adjacent air space.

• Radiant Barrier Spray
  • What Is Radiant Heat Gain?
  • And why is my House So HOT?

It all starts with the Attic. Have you ever gone into your attic on a hot summer day? Did you know that the attic temperature in most homes can reach 140-160 degrees? Ideally, there would be no difference between the OUTSIDE air temperature and the air temperature INSIDE your attic.

Two things:

1. RADIANT HEAT GAIN
2. INADEQUATE or IMPROPER VENTILATION

Our Spray-On Radiant Barrier acts just like a mirror and will block or reflect 78% of the radiant heat from ENTERING the attic. This will make your whole house cooler and more energy efficient. Radiant Barrier Spray...Blocks The Heat!!

• 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.
  • Reduces energy requirements, which lowers utility bills.
  • 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.