Insulate Against Fire

Shutterstock/ Arturs Budkevics
Shutterstock/ Arturs Budkevics

As a home ages, an owner can take many steps to make it more energy-efficient and lower heating and cooling bills. Adding a UV-light glass coating to windows will keep sunlight out. Installing double- or triple-paned glass windows with pressurized Krypton gas space between the panes will reduce heat transfer. People in hot and cold locations use attic insulation to lower energy costs, which can have short- and long-term effects on a home’s electrical system.

Care must be taken before and after adding attic insulation to a home, especially an older home. Electrical contractors should always be contacted prior to doing this work. Extremely old homes may have knob-and-tube wiring in unfinished attics and roof spaces. This is still covered in Article 394 of the NEC .

Concealed knob-and-tube wiring cannot be used in the hollow spaces of walls, ceilings and attics where the spaces are insulated by loose, rolled or foamed-in-place insulating material that envelopes the conductors. Knob-and-tube conductors were designed to be open-air conductors and not to be placed where they could be enveloped in attic or wall insulation. If the insulation envelopes the conductor, it can prevent the dissipation of heat into free air, breakdown the conductor insulation and possibly ignite combustible materials. Open, free air around knob-and-tube must be maintained. This application is becoming less of a problem as the older wiring systems are replaced, but older buildings may still have this wiring.

Blown-in insulation may also pose a problem to recessed incandescent luminaires, especially in homes built before April 1, 1982. As of that date, recessed incandescent luminaires must have thermal protection and must be identified as such. Prior to that date, that protection was not required.

In the 1981 NEC Handbook, the commentary for 410-65(c) stated, “Energy conservation measures have led to the installation of additional thermal insulation in attics. Many fires have been reported on recessed fixtures where thermal insulation is installed directly around the fixtures. The possibility of fire exists if the insulation is installed so as to entrap the heat of the fixture and prevent the free circulation of air.”

This thermal identification on recessed incandescent luminaires doesn’t help the homeowner, insulation contractor or the EC, since the marking may not be easily visible in an existing attic application. Fires have been directly attributed to blown-in insulation that has accumulated around recess incandescent luminaires that are not thermally protected.

Where the blown-in insulation envelopes the recessed incandescent luminaire provided with thermal protection, the incandescent lamp will operate for a certain length of time and, when the thermal protective device heats up to a maximum temperature, the lamp will cycle off until the device has cooled and then the lamp will come back on. The fix for this cycling on and off is to go into the attic and clear the insulation from around the recessed luminaire. Cycling may also be caused by installing an incandescent lamp that is too large or installing the wrong trim on the luminaire, thereby trapping heat and causing the cycling. In that case, the fix is easy and, when the proper lamp or trim is installed, the lamp will stay on and provide the consistent, necessary illumination of the area as originally designed.

An electrical contractor must be careful when trying to troubleshoot over the phone. They should ask the homeowner the age of the home, if insulation has recently been blown into the attic and if an incandescent lamp in a luminaire has recently been changed. The homeowner may not be knowledgeable enough to properly size the lamp based on the type of luminaire or trim to answer your questions.

Even with the advent of LEDs and compact fluorescent lamps, many homeowners still don’t understand the issue about proper sizing of the lamps and the heat that may build within the lamp and the base that may affect the thermal protection device. It is best to determine the cause of the problem before seeking the proper solution.

About the Author

Mark C. Ode

Fire/Life Safety, Residential and Code Contributor

Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and

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