Tag Archives: electrical safety

Radiant Barriers – Good for Energy Savings/Bad for Fire Safety

July 16, 2012 By in Energy Efficiency, General Home Issues, Health and Safety Tags: , , , , , , 5 Comments

They can cool the attic … but at what risk to the structure and the occupants?  Could radiant barriers represent a potential for harm?

Read the McDowell Owens Engineering Inc. white paper as to how “The physical and electrical properties of these materials are such that they introduce new and very serious dangers of ignition and fire.”  

The link that I had used for years to the original McDowell Owens Engineering Inc. report is no longer operating; however, you can find a pdf copy of the report by clicking here.

The summary of the McDowell Owens Engineering study is, as follows:

“1. Standard installation methods for roof sheathing with integrated radiant barrier are such that the end result is an overall environment where all of the radiant barrier material and virtually everything metal on and around the roof are electrically connected.

“2. In most cases, something in that environment is connected to earth ground. If anything in the roof environment becomes electrically energized (by lightning or any other common source) there is a high probability the current will pass through the barrier material at some point on the way to earth ground.

“3. The physical and electrical properties of reflective radiant barrier materials which we tested are such that the material in a structure provides two new and unique hazards relative to fire causation.

(a) When energized by an electrical current the material readily generates temperatures sufficient to ignite MANY materials.

(b) The barrier material itself readily serves as the first ignited material.”

If you are considering radiant barriers as an energy efficiency upgrade … if you reside in a home with radiant barriers that are installed … if you are considering a recommendation by an energy auditor or other entity to install them … read this report, first.

Electrical Safety: Some Thoughts on Knob and Tube Wiring and Insulation

June 24, 2012 By in Energy Efficiency, Health and Safety, Home Repairs Tags: , , , Leave a comment

Knob and tube electrical wiring was an early method of electrical wiring in buildings and was commonly used in North America from about 1880 to the 1930s.  While it was replaced with other electrical wiring methods decades ago, home with energized knob and tube electrical wiring still exist.

Knob and tube wiring consists of single-insulated copper conductors run within wall or ceiling cavities, passing through studs and ceiling/floor joists through protective porcelain insulating tubes.  The wires are supported along their length by porcelain knob insulators that have been nailed in place.

Knob and tube wiring runs at a higher temperature than modern wiring materials and requires a minimum of three inches of air space around the length of the wire.  This requirement adds an additional challenge to home owners wishing to add insulation in order to increase the comfort and energy efficiency of their older home.

If you have knob and tube electrical wiring in your home and plan to add insulation, first have a qualified electrical contractor inspect your wiring to ensure that it is safe prior to adding insulation.  Ensure that all connections are enclosed in appropriate protective boxes, that the wiring insulation is intact and in good condition and that it has not been modified in any manner since its original installation (addition of non-metalic sheathed cable wiring circuits, for example).

The next step, prior to insulating attics or floors where knob and tube wiring is present, is to identify and seal air leakage points.  This is an important step that will maximize the efficiency of the insulation, extend its life and assist in providing a comfortable and healthier living space.

Do not insulate wall cavities containing knob and tube wiring.

Knob and tube wiring in attics may be isolated by building a barricade around it with R-30 unfaced batts.  Ensure that the batts are at least three inches away from the knob and tube wiring.

While the presence of the older knob an tube wiring does not, in itself, violate national electric codes (though some regions forbid it), the best solution for knob and tube wiring is to replace it, if economically possible.

I’m sure that there are electrical contractors and weatherization folks who could add much to this topic and  I hope they will chime in.  Home owners should always consult a professional electrical contractor prior to adding insulation in the presence of knob and tube electrical wiring.

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