My house was built in the late 60's. It has about 3 inchs of batt
fiberglass insulation. I am getting ready to add 6 to 8 inches on top
of it,which would cover up all of my electrical wiring. My question
is, would it be safe to do that? I am worried that I would heat the
wires up and start a fire

Hi kingpen,

As long as the wiring has the coating... (an insulating plastic cover
on the wiring... white or yellow) it should be fine.  Insulation has
fiberglass in it, which is a retardant.  Meaning if a fire started in
the attic, it won't stop it but it will slow it down.

Keep insulation three inches away from recessed lighting fixtures
unless the fixture is marked "I.C." (Insulated Ceiling), which is
designed for direct contact with the insulation. If the insulation is
placed over an unrated fixture, it may cause the fixture to overheat
and start a fire. In addition, the insulation should be installed at
least three inches away from any metal chimneys, gas water heater
flues or other heat-producing devices.

The unfaced type insulation should be used when adding a second layer
of insulation in the attic, so that moisture is not trapped inside the
bottom layer of insulation.

I've provided several pages of information, easy instructions and
FAQ's for you.

*****


CertainTeed Insulation Instructions:
http://www.certainteed.com/cinsulate/cict00018fu.html
  
"Some insulation jobs you can do yourself. For most jobs, CertainTeed
recommends that you hire professionals to install insulation in your
home. If you choose to tackle the job yourself, be sure to follow a
few simple precautions and use the right tools and supplies:

• Protective glasses
• Disposable dust respirator
• Long-sleeve shirt
• Cap or hard hat (a hard hat is recommended in the attic to protect
against protruding nails overhead)

Note: Be sure to wash all work clothes separately. Then run washer
through extra rinse cycle after you remove your clothes."

Tools and Equipment

• Utility knife and extra blades
• Tape measure
• Straight edge for cutting insulation
• Stapler and staples
• Boards or plywood sheets for attic work
• Polyethylene sheeting if separate vapor retarder is needed
• Duct tape for sealing tears in vapor retarder
• Long pole for positioning pieces of insulation in attic eaves
• Baffles for soffit eave vents
• Supports (chicken wire or tiger teeth supports) for holding
insulation up under floors
   
Unfaced Insulation  (Instructional photo on this page)
http://www.certainteed.com/cinsulate/cict00024fu.html

"To install unfaced insulation, gently place the insulation into the
cavity space between framing members. It’s important that insulation
be correctly sized for the cavity and fit snugly at the sides and
ends. Wherever batts or rolls of any type are too short to fill a stud
cavity, a piece should be cut to size to fill the gap. When insulation
is too long, it should be cut to fit properly, not doubled over or
compressed.
 
To cut insulation, lay it on a board with the kraft or foil facing
down, if applicable. Lay a straight edge or 1" x 2" piece of lumber
over the area of insulation to be cut. Press your straight edge down
hard and cut with the utility knife."

*****


Owens Corning 
You’re just one day away from a more energy and cost-efficient home
http://www.owenscorning.com/foryourhome/feature_detail.asp?feature=134

"Was your home built before 1980? Do you have high energy bills? Is
your house cold or drafty?

Here are some easy steps to help you add insulation to your attic:

1. First, lay down some temporary flooring to give yourself footing.
Install a work light so you can see easier.

2. Lay the insulation blanket at the outer edge of the attic space and
work toward the center. This will give you more headroom in the center
of the space, where cutting and fitting can be done. Be careful not to
get insulated into a corner where it will be hard to get back to the
attic entry way.

3. If the joist cavities are completely filled, lay the new insulation
in long runs perpendicular to the direction of the joists, and use
leftover pieces for small spaces. If the cavity is not completely
filled, use the appropriate thickness of insulation to fill it to the
top, then add an additional layer of..."

*****


Owens Corning
http://www.owenscorning.com/around/insulation/chooseproject.asp

Adding Insulation to Your Attic
http://www.owenscorning.com/around/insulation/project/addinsultoattic.asp

"Before you add any insulation to your attic, you need to know how
much insulation (R-value) is already there. This is simply done by
measuring the thickness of your attic's existing insulation. Most
older homes have between 3" and 6" of fiber glass blanket insulation.
This is roughly equal to an R-value between R-9 and R-19.

Now click on the "R-Value Recommendations" icon below to learn your
area's recommended R-values. (The U.S. Department of Energy recommends
how much insulation homes in each area of the country should have to
achieve optimum energy efficiency.)

Subtract the amount of your attic's existing insulation from your
area's recommended R-value to determine how much more should be
installed. MIRAFLEX® insulation is great for adding a second layer to
existing attic insulation because it is virtually itch free. MIRAFLEX
R-25 insulation comes in compact, continuous rolls which makes it
especially easy to roll out in the attic."

[edit]

Scroll down the page and you'll find accompanying pictures to the
following directions:

"First, some temporary flooring should be laid across the joists to
provide some footing, and a temporary work light should...
 
Lay the insulation blanket at the outer edge of the attic space and
work toward the center. This allows for more headroom in the center of
the space, where cutting and fitting can be done. It's also a good
idea not to get "insulated into a corner" where it will be hard to get
back to the attic entry way.
 
If the joist cavities are completely filled, lay the new insulation in
long runs perpendicular to the direction of the joists, and use
leftover pieces for small spaces. If the cavity is not completely
filled, use the appropriate thickness of insulation to fill it to the
top, then add an additional layer of insulation in the perpendicular
direction.
 
The insulation should extend far enough to cover the tops of the
exterior walls, but should not block the flow of air from the eave
vents. To make sure the eave vents aren't blocked, Owens Corning
Raft-R-Mate® attic vents or baffles should be installed to provide
unrestricted air flow from the soffit to the attic.
 
Insulation should be kept three inches away from recessed lighting
fixtures unless the fixture is marked "I.C." (Insulated Ceiling),
which is designed for direct contact with the insulation. If
insulation is placed over an unrated fixture, it may cause the fixture
to overheat and perhaps start a fire. Also, the insulation should
always be installed at least three inches away from any metal
chimneys, gas water heater flues or other heat-producing devices.
 
Around masonry chimneys or other areas that have small openings, stuff
these spaces with small pieces of unfaced insulation, which will not
burn.

Project Tips:
http://www.owenscorning.com/around/insulation/project/addinsultoattic_tip.html

"Second Layers of Insulation 

When adding a second layer of insulation in the attic, the unfaced
type should always be used so that moisture is not trapped inside the
bottom layer of insulation."

*****

Easy2Technologies
http://www.easy2diy.com/cm/easy/diy_ht_index.asp?page_id=35693802

"The second layer should not have a vapor barrier because moisture
could potentially get trapped in between the two vapor barriers. This
second layer will make it easier for you to obtain the recommended
R-value for your climate."

*****


From Doityourself.com... Preparation
http://doityourself.com/insulate/insulationprep.htm

1. Have a pencil and paper and a trouble light with an extension cord
before going up to your attic. Carefully examine your attic space
before you begin. Determine whether you will be using the space for
living and want to heat it or prefer to just insulate the main part of
the house below the attic.
2. If you wish to finish and heat the attic space, look closely at the
rafters, checking them for depth and uniformity. They must be adequate
to house the depth of batting needed for your area. Furring out the
rafters to the proper..."


Installation of Fiberglass Insulation in the Attic 
http://doityourself.com/insulate/insulationinstall.htm

"Working on your knees in a hot attic for long periods of time can be
very tiring. Plan this phase to take a few breaks in your work time.
Try to work early in the morning before it gets too hot. You will be
covered from head to toe in clothing and gear. It may help to add a
spray container of cold water to your tool box to spray on yourself
and your fogged up goggles..."


Fiberglass Insulation Most Common Mistakes  (please read entire list)
http://doityourself.com/insulate/insulationmistakes.htm

1. Not providing for good air circulation between the roof and the
insulation

2. Neglecting to find out the most efficient R-value for your area and
insulating accordingly

3 Installing fiberglass batting with the paper side (vapor barrier)
facing toward the outside...

*****


Frequently Asked Questions
http://www.owenscorning.com/around/insulation/faq_attic.asp

*****

For my search I questioned _at length_ the Home Depot Insulation
Manager

Google Search:

Owens Corning, CertainTeed, second layer attic insulation safety, how
to add second layer insulation, fire safety wiring attic insulation,
batt fiberglass

Best regards,

tlspiegel

---

Request for Answer Clarification by kingpen-ga on 03 Aug 2003 12:21 PDT

I do not know what kind of insulation is on my wires. I believe it
might be some kind of asbestos. Where it is worn, you see what looks
like fibers. What I want to know, will these old wires covered up with
added insulation start a fire.

---

Clarification of Answer by tlspiegel-ga on 03 Aug 2003 12:32 PDT

Hi kingpen,

My answer said in the first sentence: "As long as the wiring has the
coating... (an insulating plastic cover on the wiring... white or
yellow) it should be fine.

Nothing in your question indicated wiring that was compromised.  So I
proceeded to answer as such.

My answer was dependent on the wiring being in good condtion with the
insulating plastic cover intact.

Then you said in your clarification: "Where it is worn, you see what
looks like fibers. What I want to know, will these old wires covered
up with
added insulation start a fire."

*****That definitely changes the picture.  You didn't mention in your
original question that the electrical wiring was worn in any way!*****

If an electrician **corrects** any defects in your present wiring,
then adding a second layer of insulation will not be harmful, as long
as all precautions and directions are followed exactly as suggested.

Best regards,

tlspiegel

tlspiegel may be correct that most electrical codes allow electrical
wiring to be burried deep in fiber glass insulation, but I am
skeptical as a temperature rise of several hundred degrees could occur
if the rated current is drawn for several hours. This would be very
bad news with styrafoam or treated paper insulation as toxic fumes
would result.  Neil

In reference to the 'comment' made by neilzero - the customer did not
ask about styrofoam or paper insulation.  Using fiberglass produced by
OwensCorning or a similar company is what the customer asked about,
and is used predominately because of safety and without fire hazard,
as long as all precautions are taken as provided in my links.

Regards,

tlspiegel

The current carrying capacity of cables is related to their ability to
lose heat generated by the current flowing though them. Electrical
regulations (at least in the UK) have different ratings for a cable
according to its mounting method. However, as the existing cables are
already running within or in contact with insulation, derating should
have already been applied, so this is probably not  a concern. The
calculation can always be checked for the cable size and circuit
rating against the appropriate table in the electrical regulations to
make sure.

Cable insulation (PVC) can be damaged if it comes into contact with
polystyrene insulation. However, the insulation being used is
fibreglass, so this also should not be a problem.

Owain