Important Non-Energy Considerations
Potential for moisture condensationCondensation can be a concern when a radiant barrier is installed on the attic floor directly on top of conventional insulation. During cold weather, water vapor from the interior of a house may move into the attic. In most cases, this water vapor will not cause any problem because attic ventilation will carry excess vapor away. But, during cold weather, a radiant barrier on top of the insulation could cause water vapor to condense and even freeze on the barrier's underside. A radiant barrier used in the attic floor application must therefore allow water vapor to pass through it. Some allow water vapor passage through holes or perforations, while others are naturally permeable. Some testing has been performed to determine the potential for moisture condensation with perforated radiant barriers laid on top of the insulation. A test was conducted during the winter in Climate Zone 4, using houses that were operated at much higher-than-normal indoor relative humidities. Since this testing did not reveal any significant moisture condensation problems, it is expected that moisture condensation will not be a problem in warmer climates
Attic ventilation helps to cool your attic in the summer and to remove excess water vapor in winter. Unfortunately, specific recommendations for the best type and amount of attic ventilation for use with radiant barriers are not available. Where no ridge or gable vents exist, it is recommended that one or the other be installed. Always check existing ridge vent systems to ensure that roofing paper is not blocking the vent opening, and check the soffit vents to ensure that they have not been covered with insulation.
Effect of radiant barriers on roof temperatures
Field tests have shown that radiant barriers can cause a small increase in roof temperatures. Roof mounted radiant barriers may increase shingle temperatures by 2 to 10oF, while radiant barriers on the attic floor may cause smaller increases of 2oF or less. The effects of these increased temperatures on roof life, if any, are not known. Some shingle manufacturers will not warrant their shingle with a radiant barrier whereas others will. Check with the manufacturer before selecting a shingle for a new roof.
The fire ratings of radiant barriers are important because flame and smoke characteristics of materials exposed to ambient air are critical. To obtain these ratings, a material must have an ASTM E-84 Flame Spread Index test and the resulting rating must be printed on the product. Rating requirements vary depending on whether or not the attic is accessible and may also vary from one code jurisdiction to another. You should check to see if your local building codes have any other requirements.
Other safety considerations
- The installer should wear proper clothing and equipment as recommended by the radiant barrier manufacturer. Handling conventional insulation may cause skin, eye, and respiratory system irritation. If in doubt about the effects of the insulation, protective clothing, gloves, eye protection, and breathing protection should be worn.
- Be especially careful with electrical wiring, particularly around junction boxes and old wiring. Never staple through, near, or over electrical wiring. Repair any obvious frayed or defective wiring in advance of radiant barrier installation.
- Work in the attic only when temperatures are reasonable.
- Work with a partner. Not only does it make the job go faster, it also means that you'll have assistance should a problem occur.
- If the attic is unfinished, watch where you walk. If you step in the wrong place, you could fall through the ceiling. Step and stand only on the attic joists or trusses or the center of a strong moveable working surface.
- Watch your head. In most attics, roofing nails penetrate through the underside of the roof. A hard hat may be of some use.
- Make sure that the attic space is well ventilated and lighted.
Do not cover any recessed lights or vents with radiant barrier material (attic floor application).