adding insulation to an attic

Mike T., Swampeast MO

Not a good idea to surround knob and tube wiring with insulation. Heat buildup leading to fire is a possibility even if a California study could not prove this being the cause of any fires. When you completely embed, you can no longer see. If you don't have something solid protection the K&T it's easy to hit, step on, etc.

The gaps in the roof boards are there because there was originally a wood shingled roof. Such roofs REQUIRED open sheathing to allow the shingles to dry from the back side.

Toddj_2

adding insulation to an attic

Hi all,

I'm adding insulation to the vent space above my third floor (attic) of my 140 year old home, in Soutern New Hampshire. It is a duplex and half the house has newer romex wiring (installed in past few years)..and the other has a mix or some newer romex but also some old nob and tube connections..

So the total gallon usage of the house is like 2400 gallons a year. This is why I have decided to add the insulation, I doubt that I am ever gonna "over insulate). When I say add insulation..I mean there is a mat of blown in already there.
But I doubt it is enough insulation because of my gallon usage and how quickly snow melts off the roof..
The current vent area is quite large, you can actually stand up over 1/2 to 2/3 of it..and it has venting on both gable ends...plus there are gaps in the roof boards (probably to add venting when the house was heated by coal units way back when a friend told me)..


So these are my questions:

1. I laid r-25 insulation over the blown in..perpindicular to the joists..like a blanket.. The blown in is about 4-6 inches thick..I havent measure the width of the joists.
Does anyone think this is too much insulation?

2. Also I am not sure how close to the nob and tube I can go. It is unfaced insulation. Anyone with any experience in this?

Thanks Todd

Big Ed

Time for up grade

Knob and tube wiring is a unsafe and out dated system. Was installed to replace gas lighting. It's a unprotected with no grounding and not adequette for a modern home.... It's time for a change...

Dean_7

Knob and Tube wiring

I'm just a homwowner but again from personal experience when our home (103 years old) was rewired a few years ago the knob and tube wiring still in the attic looked fine . But only on the surface, it had been severly degraded by time and the heat in the attic to the point that if flexed big pieces of insullation broke off. It was extremely hard and brittle. Also the electricians told us that Knob and tube wiring was NOT designed to be covered in any way shape or form. It can't dissipate internal heat and becomes a fire hazzard if covered.

LKE

urban legends

Fuses, they protect any wiring system from heating up the wires, knob and tube wire sizes are like any other system and if anything they can dissapate heat better than romex.
There is a different concern with covering knob and tube with insulation, it's the connections, on knob and tube the connections were made by stripping the wire and wrapping it around a similarly stripped section and then soldered and taped. These are good connections, they were made by the dead men. The problem is when modern day mechanic whose understanding of science is not up to the task and he makes the connection by wrapping the wires but leaves out the solder. This connection will heat up depending on the load and if covered with insulation can lead to a fire. The issue of the wire insulation becoming brittle I am quite sure is from oxidation not heat. The culprit here I think is rubber used on old wires which over time becomes brittle.

Ron Schroeder

Fuses do NOT protect wires from heating up. Wire will heat up based on it's size, current flowing thru it, air flow and any (thermal) insulation. Fuses only protect the wire in a fault condition.

Covering knob and tube wiring with insulation is a bad idea. And it's against NFPA code. It will reduce their current handling capacity since the heat can't be drawn out of the wire into the surrounding air. Any condensation in the insulation will also be corrosive to the wire. Hiding the wires with insulation also makes them less "protected" from mechanical damage.

My suggestion, replace the wiring with romex or other locally approved wiring method and blow cellulose in the attic.

Ron Schroeder

toddj

Thanks for you're input on the wiring...I guess I'll get my electrician over here to replace it..it is only one run..and at that is just for lights....
However I am confused still by the covering issue because the wire connecting to ceiling light has been covered in blown in insulation for well over 20 years and obviously no problem..

Also the issue of adding R-25 fiberglass batts on top of 4 inches of blown... no one addressed this question? Anyone know if that is too much in Southern NH..I have no idea of R Value of the blown in..but as I said roof snow melts quicky sun or cloudy in winter..

Todd

Mike T., Swampeast MO

Cellulose and fiberglass are the most common forms of blown-in insulation. Cellulose has an r-value of about 3.5/inch; fiberglass about 3.2/inch. NO, R-25 batts on top will not be too much.

If that K&T can be replaced, I would suggest such.

SVDW

snow melting

I didn't see anything posted about venting. Does your house have soffit/roof vents to allow the heat out in the winter? Some houses never had vents installed & need to have something put in. It will not only prevent ice damming but will extend the life of the roof by allowing moisture/humidity escape. If it has vents are they plugged by existing insulation? You will always have some heat escape into the rafter area no matter how good you insulate & you need to give it a way to escape. Maybe you are aware of all this & if so good luck & sorry for wasting your time. Otherwise do a little 'net research on proper venting & I think it will be worth your while. I quote commercial buildings for a living & one of the biggest challenges (& lawsuits) we see are involving climate/atmosphere in buildings. (mold growth,mildew, ect.)

Dirk Wright

In your area, you need more like R40 up there. I live in Virginia, and the DOE recommends R38 for the attic. The DOE web site has a calculator for determining the proper amount of insulation for your area.

Fuses and circuit breakers are there to protect the insulation on the wires, not the wires themselves, which can take much more heat than the insulation. If the insulation on the wires is compromised, then the wires have to be replaced. Corrosion on the wires nad/or connections increases their resistance which increases the amount of heat they generate for a given load, making the insulation break down before the breaker or fuse trips, leading possibly to a fire.

toddj

soffitventing


Thanks for the recent comments regarding the insulation. Sounds like I'm not over-insulated.

As far as venting..I do know I have old style gable vents..and the vent area above the attic is high enough to standup in..so hopefully that will take care of the vent problem..I do plan on installing a ridge vent when roof is re-done in a few years..but can only do so much at one time.

With regard to the knob and tube wiring..I guess I'll just play it safe and have it replaced..as I said earlier it is only connected to 3 lights (the outlets are on the new romex).

Todd