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Faced or Unfaced Mineral Wool Insulation?

1chipster's picture

I just located another brand of mineral wool batt that is available foil faced.  Roxul is only available unfaced. So it's back to my attic in greater Boston that has no insulation. What is the best type to use in this situation?  Also, I noticed  that there is BX wiring running in some areas on the attic floor which provides electricity to  old ceiling fixtures downstairs.  There are no electrical boxes in the attic, the cable just goes thru the attic flooring.   Do I have to keep  this insulation 3 inches ? away from this wiring when I insulate? Would it be better to use unfaced batts in these areas vs foil faced?     Thanks

There's no need to keep (post #206912, reply #1 of 4)

There's no need to keep insulation away from BX (though knob-and-tube is a different matter).

Foil-faced is a little touchy, however, since there's a very slight danger that the BX shell could become "hot", and the foil (if against the BX) could conduct the juice to a more distant location, increasing the danger of shock and more slightly increasing the danger of fire.

Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Would you reccomend only (post #206912, reply #2 of 4)

Would you reccomend only using the unfaced product for the entire attic then?

i would air seal first then (post #206912, reply #4 of 4)

i would air seal first

then blow borate treated cellulose

you can rent a blower

my nephew blew his attic in Malden with a leaf blower

Mike Smith Rhode Island : Design / Build / Repair / Restore


What and where is the vapor barrier? (post #206912, reply #3 of 4)

I think I remember that Greater Boston gets cold part of the year. 

The foil will act as a vapor barrier.  If it is on the top, and exposed to the uncondtioned air in the attic, the vapor will stop there and freeze up.  The ice will get progressively thicker through out the winter, untill a warm day in spring, at which the ice melts.

If there is lots of ice, there could be enough water to cause immediate damage.  Less ice, there is enough to saturate the rock wool, causing mold issues.