Remove old rockwool before new insulation?

Stephen S.

I am living in a house built in mid-80's in Seattle, Washington (zone 4), I'm planning to install more insulation in the attic.

I believe the attic has rockwool? insulation around 3-4 inches high and there's no vapour barrier beneath the existing insulation, just resting on the ceiling drywall.

Should I have someone remove the old rockwool insulation and start all over or just put the new unfaced insulation roll on top of the existing rockwool?

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Windows on Wash

That is most likely cellulose and not rockwool.

No need to remove it, however, you must-must-must air seal prior to installing more insulation.

That flue (assuming that is) pipe also need to be clearanced from the insulation and should not be in direct contact with the insulation. Isolate out with fire rated drywall or sheet metal.

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Big Stud

Yep, that is cellulose. Rockwool is what we used to call the "Brown Death". Nasty stuff it is. Is good for firestop and insulating though.

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All the best to you and yours, Tom

Stephen S.

Thank you for identifying the cellulose! No removing the material so no vapour barrier is needed or is it better to have that ?

Is it better to use blown cellulose or the fiberglass rolls we get from big box stores ?

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joecaption

Just lay unfaced fiberglass over it laying in the oposite direction.

tibberous

Not a big fan of cellulose, but seeing as how you already have it, would it make more sense to just add more cellulose than try to put something over or in place of it?

I think they make big vacuums just for removing it.

Windows on Wash

No vapor barrier is required in your zone and even it were, it would be across the ceiling and the warm side. It is not required in your case but you would be well advised to air seal the attic floor and all the penetrations to prevent the bulk movement of moisture laden air into the attic.

Cellulose is a far better insulated than its blown in fiberglass counterpart. Batt fiberglass (when high density) is okay but more labor intensive to install and requires the surface to be uniform and level for proper alignment and to prevent any air movement between sections.

The big vacuums are for extracting blown in material regardless of being cellulose or fiberglass.

What is it that you are not a fan of with cellulose?

While okay, conditional on using a high density batt, this application is about 2X the work to do properly than blowing in cellulose.

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tibberous

Doesn't seem to work very well in my house, which I'm sure is partly to do with it being added after the fact. When you put it in to a cavity, it seems to clump and leave big open pockets.

Windows on Wash

That has everything to do with the quality of the cellulose, blower used, and installer capability.

Good cellulose is well know for settling out nicely an filling voids very well.

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