IIRC knob and tube used insulated wire, but I can see some validity in
the its getting more convection cooling because it was free standing
between the insulators (knobs) whereas romex is usually stapled against
wood and often covered by insulation too.
Wouldn't bet on it without seeing the old specs myself though.
You are right that it is insulated. Of course by now a lot of it is not
all that insulated.
However you are at least a little off on the wire gauge thing. I am
not quite old enough to know if they originally required or used larger
gauge wire for a circuit. The stuff I have worked with did not. In fact it
used smaller gauge wire. The physical separation and the ability to
dissipate heat allowed it to carry the additional current per wire size.
Generally you would want to have vents along the eaves of the roof, then
vents at the peak of the roof and a clear path for the air to flow as
pictured on the following web page.
So best to have this type of air flow and to not block that air flow with
So far as the knob and tube wiring, I would have it all replaced with romex
if it is acceptable to cover the romex in your area with insulation, then
not to worry about that.
So far as the recessed lighting, no matter what the label says, these can
get *very* hot and damage/melt the insulation on the wiring. I would have
the electrician verify that these are wired with appropriate new high heat
rated wiring. Then I would also be sure to not cover them with any
insulation so the heat can dissipate.
So far as how much insulation, with the current high energy costs, I would
add as much insulation as possible to the attic and also add the roof top
insulation. It will probably be worth it in the long run. I don't know what
your heating and cooling costs are, but if you want to lower them, then
consider the cost of this work -vs- the cost of added insulation.
And so far as spray foam around the existing electrical boxes for ceiling
lighting, again these can get to be quite hot as heat travels up. I would
re-wire with appropriate new high heat wiring and ask the local building
inspector what is allowed. I have seen these where the heat from a regular
light bulb has caused the insulation on old wiring to fall to pieces
leaving bare wire (was not high heat rated wiring). Personally I would tend
to want to leave a little ventilation above these just like the recessed
Overall, your area may require a building permit to install insulation.
Good idea to get a permit and discuss your plans with a local building
inspector before the work is done, then have it inspected after the work is
done. If no permit is required, might want to see if you can pay a building
inspector to check it out in their spare time or something - make
suggestions as to what would be best.
Good idea here. Your climate may see less benefit and a longer payback
period but it couldn't hurt.
Ventilation is very important in attics and will prolong the roof life and
eliminate rot, etc. I would make sure there is some airspace between the
roof sheathing and the insulation AND that there is a way for air to enter
Given that this is a flat roof, there are products that can be added on top
for insulation. they are not 1/2" thick, they are about 3 or 4 inches thick
urethane. Here is one of many
If I insulated the 'attic' I would leave airspace and add vents.
That pipe may or may not be adequate. There should be a place for air to
enter and exit under the entire roof.
That would be best answered by a heating AC guy. Are you getting hot or
having trouble staying warm or both
? You may never see a payback or ROI. You could in a year. Too hard to tell.
Its about R5 per inch. They are most likely talking about a 3" product. make
sure they are then that price may be OK. its definitely not for a 1/4"
They are cheap - Just get an IC rated can if you are adding the insulation
and venting. Do not mess with non-IC in an insulated area.
Don't worry about it - Very little, if any, will leak out.
So - To sum it up. If it were me. I would add a 4" ridged foam on top of my
roof sheathing before I had my new flat roof installed. Before it was
installed I would have some sheathing removed so my K&T wire could be looked
at. If the insulation was crumbling off I would have it replace with romex.
If it was fine I would leave it alone. Maybe at this point I would have my
recessed light installed. I can use the one I have because I'm not putting
insulation in my 'attic'.
Our advice is free, take it for what its worth.
I'd replace all the knob and tube wiring with romex while you have
access to that area. I'd only use IC rated lighting. I also would not
fill the entire space with insulation. There should be air space with
vents for a way for air to enter and exit above the insulation. This
keeps the temps down and prevents moisture problems. Plus in your
area with milder climate, you can get by with less insulation.
How about the p2000 foam insulation: http://www.p2insulation.com /
For 1 inch, installed with seams properly taped and an air space like
you have, you can get close to R-40. Yes... 1 inch... r-40. It's
expensive but great for limited space. A number of the timber framers
around here are starting to use it since it's so useful for limited
space areas. The 1 inch of p2000 gives better r-value than the regular
rigid foam they used to use. I understand it's been used commercially
for some time and is just now getting onto the residential market. From
the literature it seems it gets it's high r-value by addressing
radiative and conductive heat along with a vapour barrier all at the
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