Add or Replace Insulation

[Dragonrider99]

Greetings all. I have a 50 year old house that has 2" thick insulation laid in the attic. The insulation appears to be faced on both sides and made of.... cotton??? There is no floor installed so I will be laying the new batts directly between the floor joists. My question: Can I lay the new insulation directly over the old? If I can, should I use unfaced or faced? I understand that if it was not insulated, I would lay the new insulation faced side down. I am confused as to which way to proceed. It would be nice to keep the existing material as it would add to the overall thickness and "R" Value. The house is vinyl sided and has a continuous soffit vent. I understand that I should lay the batts right up to the external wall, leaving the sooffit vent exposed. How should I proceed with the old and new?

Thanks

[Sweep]

Here is an answer I gave to an earlier member with the same question:

Your attic is undoubtedly insulated with a mineral wool commonly called "rock wool" made by spinning and blowing air into melted basalt & limestone. Today, it is primarily used for firesafing, spray-on fireproofing, and acoustic insulation. The R value is better than fiberglass so its not a bad thing to have in your attic as long as you don't disturb it. The fibers are unusually irritating although not considered a carcinogen.

I would cover it with unfaced fiberglass.

[danh]

A very smart man was once quoted as saying something along the lines of "unlike vapor barriers, you can never have enough air barriers in an assembly"

As long as the facings are breathable (high perm ratings), you'll be fine. Same with the fiberglass facing.

And who knows; it may actually be cotton.

[Sweep]

Facings on modern batt insulations are put there to act as vapor barriers but the facings on the rock wool are probably to make it easier to handle. Rock wool looks very much like dirty cotton but you can easily tell it isn't because it's a terrible irritant to your skin, eyes and lungs. It's best not to disturb it.