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Radiant Barrier
Energy Efficiency, Comfort, and Health | Function and Optimal Operation | Components and Options | Radiant Barrier Sheets | Radiant Barrier Chips | Radiant Barrier Paint or Spray | Cool Roof | Low-E WindowsQuick Facts
- Protects homes in hot climates from summer heat gain by reflecting radiant solar energy
- As only one part of the building envelope, installation of a radiant barrier must always come after the house has been thoroughly air sealed and insulated
- Radiant barrier is generally a reflective surface (often foil) installed in the attic or under roofing
- Foil works the same way as low-e windows and cool roofs, but is generally much less effective (although it is cheaper as a retrofit)
- Expect 0% to 10% savings on cooling costs for foil barriers, depending on climate, insulation level, and duct placement (greater savings for ducts in the attic, which heats up more than the crawlspace)
- Savings in cold climates will be minimal and may increase winter heating costs (by reducing natural warming of the home by the sun)
Energy Efficiency, Comfort, and Health
The building envelope is what separates your home from the outside world. Using a radiant barrier as part of a properly engineered building envelope may reduce the load on your cooling systems by avoiding some heat gain from the sun. This can help increase the comfort of your home while also making it more energy efficient. Reducing the amount of energy needed to make the home comfortable can be even cleaner than using renewable energy since the cleanest energy is the energy that isn’t produced or used in the first place.
Function and Optimal Operation
In any climate, the positive effects of insulation and air sealing can be magnified by the application of a radiant barrier; the effect will be felt more in hotter climates and when used in conjunction with air sealing and insulation. Comprised of reflective material, a radiant barrier may protect your house from heat transfer along the building envelope by reflecting some heat out in the summer. This is different than insulation which slows the passage of heat through a material.
The best application of radiant barriers is when the house is in a climate which needs cooling and has either the air conditioner or ducts in an unconditioned attic.
Components and Options
Radiant Barrier Sheets | Radiant Barrier Chips | Radiant Barrier Paint or Spray | Cool Roof | Low-E Windows
All systems are made up of functional components. These types of radiant barriers are appropriate for different spaces and situations in a home. As such, different forms of radiant barrier can be used in the same house. It is vital the building envelope be thoroughly sealed and insulated for a radiant barrier to be most effective, since air sealing and insulation protects against different forms of heat gain. Regardless of the level of weatherization in a house, some forms of radiant barrier have little or no proven value for reflecting heat.
Radiant Barrier Sheets
The includes any rolls of insulation consisting of a reflective foil-like sheet which may or may not be mounted on polyethylene bubble, wrap, batt insulation, or other forms of thermal insulation. It must be installed with the reflective side exposed to the air since it functions by reflecting radiant heat energy. Sheets of radiant barrier should be attached to attic rafters (not spread over the attic floor), installed in a way that dust and debris will not settle on the reflective material, since that reduces reflectivity, reducing effectiveness of the radiant barrier. Some new construction can use materials such as roof decking or rigid foam board pre-fitted with a sheet of radiant barrier, thereby integrating the radiant barrier directly into the building envelope from the very beginning.
Radiant Barrier Chips
Another application for radiant barrier is “chips” which are simply small pieces of reflective foil which can be blown on to an attic floor. However, these have not been proven to work in the same way as foil sheets.
Radiant Barrier Paint or Spray
This can be purchased as a do it yourself paint or paint additive, or installed by a contractor. Radiant barrier paint or spray is intended to function like foil sheets (by reflecting heat energy) but very few paints on the market have been proven to be reflective enough to function correctly. Clean foil has a reflectivity of 97%; the best paints can achieve reflectivity of 77% (or 23% emissivity) under controlled conditions. Reflectivity plus emissivity equals 100%. Many paints only offer from about 10% to 30% reflectivity, or 90% to 70% emissivity. Source: RIMA.
Cool Roof
Cool roofs are becoming available in even dark colors and pitched styles (as opposed to the classic flat white roof). They generally function, like radiant barriers, by a reflective coating which reflects radiant heat from the sun instead of absorbing it. However, replacing an entire roof can be exceedingly costly and it is generally more cost effective to simply install a radiant barrier in the attic, unless the roof is to be selected for a new home or if an existing roof needs replacement anyway.
Low-E Windows
While windows are not generally referred to as a radiant barrier, high performance windows which have special low-e glazing actually function much in the same fashion: their glazing reflects heat energy to reduce radiant heat transfer. When engineering a window solution, it is important to take into account the directional orientation of the windows. When used in the right light and climate exposure conditions, low-e windows can have a dramatic effect on the building envelope and subsequent energy needs. However, since different levels of radiant reflection are appropriate for different situations (such as climate and north or south exposure) it is vital that they be engineered with the whole house in mind by a building scientist who will take into account the overall performance of the home, not just the windows. Poorly selected low-e windows can even raise a home’s energy costs. While replacing windows with high performing low-e ones may not provide cost effective protection from heat gain in all regions (they will be more cost effective in areas with more extreme hot weather), it is certainly an important step for attaining the most significant improvements. [+] MORE.