What is this insulation?

[Tom Rees]

Did an inspection yesterday on a 1925 house. The insulation in attic looked like grey moon dust (sorry no picture). You could also see an old layer of facing that had completely deteriorated. Any guesses. Should this be removed before adding new insulation?:D

[Jerry Peck]

Sell it on e-bay in 2 ounce bottles, fill 3 bottles with it, sell as "Suspected moon dust, no back up documentation available, sorry. Buy Now $99.95 per bottle. Only 3 known to exist."

And when those 3 sell, you fill 3 more, and you now have 3 more "know to exist". :D

[John Kogel]

Did an inspection yesterday on a 1925 house. The insulation in attic looked like grey moon dust (sorry no picture). You could also see an old layer of facing that had completely deteriorated. Any guesses. Should this be removed before adding new insulation?:DIt sounds like blown-in grey cellulose.

But I don't really know what grey cellulose sounds like. :) If that's what it is, it is harmless.

[Michael Thomas]

Did an inspection yesterday on a 1925 house.. you could also see an old layer of facing that had completely deteriorated

Kimsul?

[Greg Forsee]

Could be Johns-Manville Rock wool. I recently inspected a similar era home which had a label placed in the basement stating this fact. It is the mineral fiber version of fiberglass and is used [required] today as a firestopping / draftstopping material for various voids in the framing.

[Raymond Wand]

Don't see why the existing insulation should be removed prior to installing new insulation.

[Greg Forsee]

Correct; removal of the old insulation is not necessary in this case. Just make sure no facing or vapor barrier is present, just loose fill. Facings could create conditions favorable to moisture or flammability damage.

[Jerry Peck]

removal of the old insulation is not necessary in this case.

Depends on what the old insulation is.

From the description there are several things I know it is not: 1) fiberglass; 2) rock wool; 3) mineral fiber; 4) excelsior - wood fiber.

Also from the description there are several things it could be: 1) Kimsul - I had forgotten about that stuff, but Michael probably hit the nail on the head; 2) cellulose - but I doubt it; 3) vermiculite - but I doubt that too; 4) other types similar to the description.

If the insulation is like "moon dust" then I would want it removed simply to prevent its being disturbed and falling into the wall stud cavities or being disturbed by air movement through the attic during normal or abnormal ventilation.

[Raymond Wand]

Attics are under negative pressure, how is it going to be affected by normal or abnormal ventilation?

[Jerry Peck]

Attics are under negative pressure, how is it going to be affected by normal or abnormal ventilation?

Attics are under varying pressures, both positive and negative.

That insulation will be affected by the same effect as wind blowing over a field of wheat and blowing the tops of the wheat around. Not to the same extent, but we are also not talking about stalks of wheat planted in the earth either, we are talking about "dust" particles and dust is easily disturbed.

During abnormal conditions, for example high wind events, I have seen loose fill (which does not blow around anywhere near as much as dust would) where the loose fill insulation was blown 3' to 6' in from the eaves, and on a few cases where the loose fill insulation had been blown in about 10' to 12' from the eaves, leaving all the loose fill insulation piled in a ridge along the center of the house.