Cover or remove old rock wool insulation
SLewis
| Posted in Energy, Heating & Insulation on
The rock wool insulation in the attic of my 40 year old home has settled to the point that I can see sheet rock from the ceiling below. Obviously, it’s time to re-insulate. Unfortunately, the roofers who replaced the roof let bits of sheathing and cedar shake fall into the attic when the prior occupants replaced the roof five years ago. I have two questions:
1) Is it necessary to remove the old rock wool insulation before blowing in new cellulose?
2) Is it necessary to remove the bits of roofing whether the old insulation is removed or not?
Any thoughts or advice would be appreciated.
Replies
1) Is it necessary to remove the old rock wool insulation before blowing in new cellulose?
2) Is it necessary to remove the bits of roofing whether the old insulation is removed or not?
I would not remove the rock wool if it were my house. I would try to get the big chunks of roofing out.
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Greetings SLewis,
As a first time poster Welcome to Breaktime.
This post, in response to your question, will bump the thread through the 'recent discussion' listing again which will increase it's viewing.
Perhaps it will catch someone's attention that can help you with advice.
Cheers
seeyou invented nobody
Whether you have to remove it or not, depends on the weight of the insulation you would like to install, and that depends on the joist spacing, thickness of drywall, and number of fasteners used to hang it, essentially the drywall cieling supports the insulation ..
If it is rock wool, I'd probably leave it in place. I don't know of any health issues related with it. You should be able to blow cellulose right over top of it (or more rock wool). You're just causing more work and expense by removing it.
As far as removing the roof scraps, that is probably up to you. I wouldn't be up there with a shop vac sucking up all the bits, but if there were large chunks I might remove some of them just so I knew my cellulose was going in uniformly.
[edit to add] Welcome to BT!
jt8
"Democracy is two wolves and a lamb deciding what to have for dinner, liberty is a well armed lamb protesting the vote." -- Benjamin Franklin
Edited 8/23/2007 12:07 pm by JohnT8
Edited 8/23/2007 12:07 pm by JohnT8
Given the option, I would have the old stuff removed; let me tell you why.
The first reason is that the old stuff is full of dust. If nothing else, it is this dust that makes attic work such an ordeal for the sinuses.
The old stuff probably isn't insulating very well; might as well replace with stuff that works.
The roofing debris is sure to poke you in tender places whenever you enter the attic.
Finally, it is very possible that the old stuff is both holding moisture, and breeding mold. Might as well solve that problem before it IS a problem.
Now .... for the new insulation:
Before the new stuff is blown in, check everything in the attic. Make sure your air ducts are sealed, that there are no roof leaks. that roof vents are operating, and that your wiring (and lights) are suitable for burying in insulation.
Now is also a good time to enlarge that attic hatch, add lights, etc. Don't forget to put down boards wherever you will go, or store stuff.
I 'boarded' my attic by having the lumberyard pre-cut plywood into 32 x 16" pieces; these fit my 16" joists just right, and were easy to handle.
I'm nowhere near as fond of blown insulation as I once was. The only advantages to it are that it is fairly easy to get into tight spaces, and it is cheap.
On the downside, you cannot get enough depth to be effective without burying the trusses, and the equipment, in another foot or so of insulation. A visit to the attic becomes akin to a blind man stumbling through a snowbank ... groping around, feeling for trusses, and hanging up on every wire.
I don't think rock wool has a mold issue. Yes, probably dusty though. So will the new stuff.jt8
"Democracy is two wolves and a lamb deciding what to have for dinner, liberty is a well armed lamb protesting the vote." -- Benjamin Franklin
I can't speak from any position of authority ... but it sure has seemed to me that any material, when wet and dirty, will grow all manner of smelly stuff. As for dust ... sure, in another decade the new stuff will have a lot of dust in it - but that will not be in addition to the dust that has already accumulated. Not, that is, if the old stuff is removed. Maybe I'm just being unscientific and prejudiced - but decades-old stuff always seems 'yucky' and matted, compared to new stuff. Likewise, it just seems to me that light, fluffy new stuff just has to insulate better than dense, stringy, or matted stuff.
You do bring up one valid point: Removing the stuff will make it possible to do a very detailed job of air/vapor sealing.(I've often speculated that the best way to air/vapor seal an old ceiling would be to spray it with some sort of rubber-like coating -- something thick enough to bridge small holes.)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
As Dan H and Renosteinke previously noted it would be a good time
to check the vapour barrier situation. Future moisture issues and
air leakage can cost you a lot of what you hope to save with
increased insulation. A 40 year old house may have no continuous
vapour barrier at all. At the very least (assuming the ceiling is
drywall) sealing the penetrations would be time well spent.
From: http://www.us-gf.com/VaporRetarderUse.asp?Type=L
Because of its mass density (high airflow resistance) and hygroscopic properties (moisture holding), Cocoon Insulation has the capacity to store up to 30% of its weight in moisture vapor while retarding its passage by air movement. In other words, it retards the flow of moisture vapor, and performs best when moisture vapor is allowed to enter or exit from either side. The chance of any significant amount of moisture vapor actually passing completely through from one side of the Cocoon to the other is highly unlikely given the dynamics of our daily environment. Even if enough moisture vapor were present to freeze on the exterior sheathing, Cocoon would absorb it again as it melted. Make no mistake, Cocoon is not classified as a vapor retarder, since it cannot be tested by ASTM E96; the only recognized test method for classifying vapor retarders. On the other hand, Cocoon does meet the criteria on an exception since it creates an alternative construction where moisture or its freezing will not damage the materials.
By my interpretation, it seems the manufacturer of the insulation I'm looking at (US GreenFiber's Cocoon blown cellulose) is saying that a vapor barrier is not recommended because it impedes the flow of water vapor through the insulation. This recommendation appears to be specific to exterior walls and I'm interested in attic insulation where the attic has lots of soffit ventilation and roof turbines. I'd be curious what you all have to say on the necessity of vapor barrier in such an environment, and how I would go about choosing and installing a vapor barrier if one were needed. For the record, the house is just outside Kansas City.
Good call on checking for air leakage. That may be reason enough to remove the old rock wool and fill any gaps with caulk or expanding foam. I guess the best approach to remove the old insulation would be a shop vac and a helluva lot of trash bags.
For what it's worth, I already have or will be repainting all of the ceilings with Glidden's EZ Track from The Depot. I'm not sure if this constitutes an adequate vapor retarder, but I thought I'd throw it out there anyway as a point of consideration.One other point, I've added bathroom fans to all attic-facing bathrooms that vent through insulated ducts running out through the soffit. There are several recessed cans, all of which are IC approved.
Edited 8/27/2007 1:45 pm ET by SLewis
Forget for a second about vapor barriers. In an attic, more than in walls, you need to worry about infiltration sealing. While cellulose is much better at managing infiltration than fiberglass, it's still important to seal cracks and penetrations in the ceiling.That article confuses me and seems to be speaking at crossed purposes. Around here, eg, (and I'd guess much of the snow belt), felt isn't typically used on outside walls, but rather housewrap is, and most housewrap is designed to be relatively transparent to water vapor. Also, it's rarely the case that inside temps are lower than the outside dewpoint (at least not for very long). So I can see no valid argument for not using a vapor barrier (and considerable argument for using one).The cellulose folks probably are arguing mostly to justify blown-in retrofits, where there is no worthwhile vapor barrier and retrofitting one is impractical. Certainly cellulose is still a viable option in most such cases, but that doesn't say that a vapor barrier isn't worthwhile.(You'll notice that they don't claim that the insulation can retain 30% of its weight in moisture WITH NO LOSS OF INSULATION VALUE.)
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
Depending on your ceiling it may be easy to seal leaks just by moving
the old insulation around. Taking it all out would be a sure thing and
better in most respects but from a time/ money point of view it is
not always practicable. The obvious leaks will be around some ceiling
light fixtures, top plates of interior walls, plumbing and electrical
penetrations etc. Its often nice to clean out an old space just to
be able to spot and deal with problems hitherto unknown in a
timely fashion. I don't know about the vapour resistant properties
of your cellulose but like Dan I have concerns and certainly prefer
the tried and true methods. I welcome a chance to learn from others
who experiment at their own expense. The disclaimer is that my
experience is relevant to Ottawa and other locations have different
needs. Oh yeah, you can also consider making bandaid type patches
with poly and caulking where applicable.