Is cellulose a bad idea to insulate a frequently-used attic?

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MattinCA

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1950s Southern California tract house with about 1200 SqFt attic. Basically, noodling on Home Depot's website, it looks like blown-in cellulose is about 1/3 the cost of fiberglass batts or rolls. But the center of the attic is decked and used for storage, so I am concerned about the dust issue since the attic will be accessed frequently (some say they get dusty and dirty every time they go in their cellulose-insulated attic).

Can anyone speak to their experience with the dust issue in going in and out of a cellulose-insulated attic? If you think dust is an issue, would a good solution (for the areas not covered with decking) be to use cheaper cellulose just to the top of the joist bays then lay perpendicular fiberglass batts over the cellulose to get the needed R-value and hold the dust in?
 

Guzzle

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Fiberglass dust can be a nuisance & sometimes toxic, the other can be classified as a non-toxic nuisance.
A rock & a hard place. :(
 

Snoonyb

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Insulating an attic should 1st be concerned with baffling the attic vents, and from there, I have installed unfaced batts, throughout the LA basin, as a 1 person operation.

R-19 is the recommended for that temperate zone, and where there was compacted cellulose product, it was removed and the batts placed, and where the home owner has accomplished additional weather related upgrades, additional unfaced batts, often R-30 were added perpendicular to the R-19.

Cellulose may sound inviting, until you add the additional person needed to feed the blower.
 

voyager

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Cellulose insulation, assuming nothing has changed with it through the years, is nothing more than ground up newspaper.
Calling it cellulose comes from the fact it is a wood product (from paper), with an attempt to make it sound like something exotic.
Blowing it in, even with a 2 man crew, has got to be cheaper than installing batts.
It always was.
Have you ever seen a blow crew exit an attic work area literally covered with the cellulose dust?
A fire retardant is added to it.
How does that affect breathing the dust?
One should wear a mask when dealing with either material.
Once they're properly installed neither produces much dust, as long as they're not disturbed.
Both are easily disturbed if exposed, and loose R value, when people move around the attic area.
Facing on a batt is little more than a poor substitute for a vapor barrier.

Personally, I'd prefer f/g batts to cellulose any day in my buildings.
It is a better, safer install, but cellulose is cheaper.

When I moved to Alaska, I spent a few years working in residential insulation, later, many years as a mechanical insulation contractor.
 
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MattinCA

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I think my answer will have to be fiberglass batts for two reasons, either one alone conclusive. Primo, we want to go in and out of the attic for storage, and secundo, because I realize we may do some remodeling or changes to the house in the future, and, for example, adding recessed lighting would be easily doable with batts and a major PITA with cellulose. Thanks for all the input.

This leads me to another question. I have 2X6 ceiling joists and it looks like I will need about 11" of height to get the R38 or so I would like. In the areas of the attic where I will not have any decking, it's no problem to fill the 5-1/2" joist cavities with batts and lay another layer perpendicular to it. But I would like to keep decking in the center 600 SqFt or so. Could I just run another 2X6 on top of each existing joist with some sort of Strongtie to effectively create 2X12s, put batts between the joists, and attach the decking to them? It would create some thermal bridging between the joist addition and the decking, but I have not figured out how to avoid that.
 

Snoonyb

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I'm not sure that the additional deck depth would be necessary, because any insulation you could stuff under the existing & the items stored will act, marginally, in concert.

Air is the conductor, in insulation.

Also, and I was remiss, in not mentioning this earlier, there are light fixtures which must be baffled to prevent insulation from encapsulating them, and this also applies to exhaust ducts associated with heating appliances.
 

Guzzle

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Placement of the vapor barrier & barrier permeability seems to depend on what type of climate predominates.
 

BuzzLOL

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1950s Southern California tract house with about 1200 SqFt attic. Basically, noodling on Home Depot's website, it looks like blown-in cellulose is about 1/3 the cost of fiberglass batts or rolls. But the center of the attic is decked and used for storage, so I am concerned about the dust issue since the attic will be accessed frequently (some say they get dusty and dirty every time they go in their cellulose-insulated attic).

Can anyone speak to their experience with the dust issue in going in and out of a cellulose-insulated attic? If you think dust is an issue, would a good solution (for the areas not covered with decking) be to use cheaper cellulose just to the top of the joist bays then lay perpendicular fiberglass batts over the cellulose to get the needed R-value and hold the dust in?
Sounds like your house isn't insulated because it's not needed much where you live. Even R-19 in the attic sounds like over kill. Are the exterior walls insulated? Dust isn't an issue with cellulose unless you're brushing against it, crawling on it, or wind blowing over it.
Don't know if it still is, but cellulose used to be ground up newspapers with some fireproofing chemicals added.
I used cellulose because the way my 200 year old house was built, the walls are open to the attic between the studs so just blew cellulose down into the walls and then on across the attic. After that, added some plywood for a storage area.
 

BuzzLOL

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Fiberglass dust can be a nuisance & sometimes toxic, the other can be classified as a non-toxic nuisance.
A rock & a hard place. :(
The newer fiberglass insulation doesn't have the itchy dust and cellulose is treated with a likely somewhat toxic fire retardant...
 

BvilleBound

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First, you have a good plan -- fill the joist bays to the top with cellulose, then cover that with fiberglass or rock wool batts. First, however, you should air seal everything in your attic before the cellulose is installed. Here are some tips:

Recessed ceiling lights are culprit #1: install Tenmat covers and seal the edges with DAP 230 sealant. See: Tenmat Model # FF130E Home Depot Internet # 204286308 Store SKU # 1000012747 and DAP 230, Home Depot Internet #100035980 Store SKU #284425 You can also make boxes to cover recessed lights with pieces of drywall; tape the corners together with foil HVAC tape (NOT silver fabric 'duck' tape) then seal the bottom edge with DAP 230 sealant. (DO NOT use spray foam because lights get hot, as noted below.)

Great Stuff foam is good to fill gaps and holes, e.g. around vent pipes and holes drilled to run electric wiring -- but do not use it near anything that gets hot, e.g. a chimney or exhaust vent. Great Stuff and similar canned foam products from 3M are VERY flammable and will ignite at just 240 degrees F -- which is significantly lower than the ignition temp of paper or wood.

For gaps near a hot exhaust vent, first pack the space with fiberglass or rock wool, then cover it with fire resistant sealant, e.g. 3M Model CP-25WB+, Home Depot Internet #100166701 Store SKU #163096 For the large gap next to a chimney, cover it with aluminum flashing (available at Home Depot) nailed to the joists, and seal the edges with 3M CP-25WB+ sealant.

When you blow in the cellulose, wear a good dust mask -- NOT the kind with a rubber band on the back. Home Depot carries 3M painter's masks with two cartridges. Both the person in the attic and the person loading bales of cellulose into the blower should wear these masks. Be sure not to block soffit vents around the perimeter of the attic, which allow air to flow in to ventilate the attic. If there is any risk that the cellulose might block these vents, install plastic vent shields first. They simply staple to the rafters. Home Depot carries them.

I hope this is helpful,

BvilleBound
 

MattinCA

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Helpful information from everyone, thanks. I am also watching webinars from PG&E (large California utility) that are pretty detailed.

I'm considering filling the perimeter bays with cellulose then laying perpendicular fg batts on top, then using the savings from using cellulose to insulate the center (which I would like to keep decked for storage on top of the 2X6's) with much more expensive polyiso sheets so could get the +/- R-38 in the 5-1/2 " available without trying to build up the height of the joists to the 11" or so necessary if I use fiberglass or cellulose with decking above it. I THINK filling cellulose only to the top of the joists then laying perpendicular batts over it would (a) keep the cellulose from being disturbed when we go up in the attic, and (b) eliminate the need to build dams to contain the cellulose.

So the decked middle of the attic would be sort of surrounded by walls of fiberglass batts +/- 6" high. Of course, this would require waiting to insulate the attic til any ceiling work (recessed lights, bath fans, kitchen exhaust fan, etc.) was done so the cellulose wouldn't be disturbed.
 
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billshack

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I had my attic insulated with 21 inches of blown in cellulose. I should have done this years ago . I also had a air-conditioning/heat pump installed , what they call a split system. my house is all electric no other form of energy. my electrical bill went from $2,000 to $1,200.
I should have done this years ago , the insulation and running the heat pump saved me a fortune.
 
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