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Old 11-29-2015, 04:24 PM   #1
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Add fiberglass rolls across joists in attic if joist cavities not completely filled?


We purchased a house with an insufficiently insulated attic. There's currently about 2-3 inches of loose-fill fiberglass insulation in between the 2x6 joists. I'd love to just roll unfaced R-30 fiberglass batts across the joists (simple, no equipment rental, very little mess), but that would leave a 2 to 3 inch air pocket between the bottom of the batts and top of the loose fill insulation. Is this a bad idea?

(We have no current problems with mold, high humidity, etc. I'd rather not create any. I don't understand the physics of this, whether it would cause problems.)
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Old 11-29-2015, 04:45 PM   #2
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When I did this in an old house with mineral wool insulation I leveled to the top of the joist with cellulose and then rolled it out.

Now that I've learned I can get it blown in cheaper that I can buy and do it I call the insulation company.
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Old 11-29-2015, 05:27 PM   #3
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How much more do you need?
You would be fay better off with blown in, less air gaps, cheaper.
Need to first air seal the attic, add baffles so the soffit vents are not blocked.
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Old 11-29-2015, 05:57 PM   #4
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I haven't found anyone willing to blow in insulation for cheaper than the price of rolled insulation; typically, I'm getting quotes that are about 3x-4x as expensive.

As far as I can tell, the price of the rolls is roughly the same as the price of blown-in fiberglass, if I install it myself.

However, the installation seems much more difficult with the blown-in insulation. I'd have to install baffles all the way around, rent the machine (or buy enough insulation that they'd let me rent it for free), haul the machine to the house, blow the insulation in, and haul the machine back to return it within 24 hours.

With the rolls, I'd just buy them, bring them home, unroll them, make some cuts to size, and hopefully be done with it.

In any case, back to the original question: is there any reason it's a bad idea to leave the air gap, ignoring cost and ease of installation considerations?
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Old 11-29-2015, 06:02 PM   #5
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Joe's advice is spot on as usual.
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Old 11-29-2015, 06:36 PM   #6
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Yes, it is bad to leave the air gap as it provides an extra space for air to circulate, and circulating air reduces the effectiveness of your insulation.

As Joe mentioned, you need to address at least the major air leaks before you bury that attic in insulation. If you If you pulled (raked) the current loose fill forward to fill the joists to the top across the middle and then cut and fit some 6" batts for the outer areas you might still be able to avoid the baffles. Then, with it filled to the tops, you could roll out your new unfaced batt insulation.

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Old 11-29-2015, 06:42 PM   #7
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Quote:
Originally Posted by Bud9051 View Post
Yes, it is bad to leave the air gap as it provides an extra space for air to circulate, and circulating air reduces the effectiveness of your insulation.

As Joe mentioned, you need to address at least the major air leaks before you bury that attic in insulation. If you If you pulled (raked) the current loose fill forward to fill the joists to the top across the middle and then cut and fit some 6" batts for the outer areas you might still be able to avoid the baffles. Then, with it filled to the tops, you could roll out your new unfaced batt insulation.
Interesting idea about the raking. Thanks, Bud. And the circulating air concept makes sense.

For some reason, the idea of adding baffles all the way around (to prevent the insulation from falling into the dropped-soffits, I think that's what they're called) seems like a lot of work to me, so this sounds like a good workaround. I'll chew on it for a bit...

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Old 11-29-2015, 11:47 PM   #8
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How long do you plan on living there?
Really want this done right once and for all and save energy?
What good does raking out not enough insulation do?
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Old 11-30-2015, 12:00 AM   #9
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Keep in mind also that while you are up there working, wear a long sleeve shirt, or go get some Tyvek Suits, so that you can just take that off into a garbage bag, in case you get dust and stuff on you. Same as wearing a face mask while you are moving stuff around.

The insulation that you have up there, can you take a photo and post it on here?

You could probably do the blown in yourself. Just make sure that you mark any junction boxes that are up there, that may get insulation covering them. Also put in the baffles at the ends of the joist bays, so that even if there are no soffits on the house. The air can still get pulled through any cracks that may allow outside air through.

Sealing gaps, I would just use a lightweight non-expanding foam, such as DAP.

As for the insulation, Home Depot will lend it to you with the bagged insulation. Just get a helper to stand below to keep the hopper full and in case it needs to be shut down so that you can take a break if you have to.

Leave the old stuff up there and just go over it with the new. We do need your location to let you know how many inches you need. The city that I live in in Illinois. I have seen anywhere from 8" of Blown in, to almost 54" on some of the newer homes.



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Old 11-30-2015, 12:54 AM   #10
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Photos below. I haven't even begun to address the question of the mess of roofing materials, the bathroom exhaust vent to nowhere, the electrical wiring (including lots of knob & tube buried under the insulation), etc. There are a lot of issues here, to say the least. But all of the above are manageable, in relatively straightforward ways.

Correction to original post: the joists are 2x8's, not 2x6's.

I'd have no idea how to go about installing the baffles. The rafters don't line up with the joists, which seems to make things complicated. Do I just install 22 1/2 vents between the rafters, curve them so that they lie in front of that 2x4 that's sitting between the rafters and the joists, cut out gaps for the joists, and tack the baffle to the floor? Sounds like a miserable job! There's not much room to work in there.

(There's a whole bunch of insulation that's fallen down in the eaves from whenever the previous job was done. I'm not sure how many of the soffit vents are covered up by the stuff. I may aim a leaf blower at all of the soffit vents from the outside, to make sure they're not obstructed. Unless there's a better way to do that?)
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Old 11-30-2015, 03:11 AM   #11
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You are going to have to get up there with a shop vac and either a small snow shovel, or a dust pan to scoop all of that up, before you start attacking the other stuff. The Knob & Tube will have to be replaced with Romex, because it is uses Air as an insulator around the jacket. Once you cover it up with any insulating material, it tends to overheat.

I am guessing that is Balloon Framing under those cripples between the rafters. Also whoever roofed that, sure did use some longer then usual nails in that one spot. If that metal duct is for a vent fan, laundry, I would just take it straight out and put in a roof exhaust vent for it.

Depending on how big of a scuttle hatch you have going up there. You may have to use 5 gallon buckets to fill and pass down to someone below to fill up say a Rubber Maid 30 gallon with Contractor bags, so that they can put the material in the bag, close it, then close a second bag that the first one is in, to help keep it from tearing. Or just rent a dumpster to toss the bags in and any other items you need to purge.

I have 6" up in mine. Had vents put in on the sides of my house when I had the house resided this past June. They were installed to help with the vents on the roof. Because the existing vents at the peak on the sides did nothing to help with air flow when we had the roof redone.

Really now is the time to start with any remodeling. If you can get the junk out of there now, since it is cooler, you can do any remodeling you need to do, without have to deal with the scraps, dust and old insulation falling through on you.



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Old 11-30-2015, 07:07 AM   #12
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Now that we hear the rest of the story, I'll retract any suggestions I made. Get up there and clean up that mess. Once all of the other issues are fixed, then you can ask how to proceed.

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Old 11-30-2015, 11:57 AM   #13
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Wear a respirator up there.

Asbestos a concern?
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Old 11-30-2015, 12:02 PM   #14
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Don't worry - I'm aware that there's a lot of work involved in getting this cleaned up and ready for insulation! I'm trying to plan things out at this point, so that I have a sense of the overall project before starting on steps 1, 2, & 3, which is getting rid of all the roofing junk, getting the knob & tube addressed (there's not much), and installing an exhaust vent for the bathroom fan ducting.

The photos are of the part of the attic that's closest to the hatch, and that's the worst-looking part. The rest isn't nearly as bad.

So - strictly in terms of helping me plan out the entire project - once the mess, the knob & tube, and the venting have all been addressed (and they will be), does anyone have a recommendation for what product to use for baffles around the eaves? I'm trying to figure that out, taking into consideration the configuration of joists and rafters.

Cardboard? Or a pre-made vinyl vent (such as "41 in. x 22 in. Accuvent Vinyl" at HD) that's flexible enough to curve in front of that gap beneath that 2x4 that runs perpendicular to the rafters/joists, tacked to the lathe on the attic floor? I'd have to cut out rectangular sections for the joists to slip into. I can't think of a better idea on my own...

Again, thank you for all the input!

I do appreciate all the input!
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Old 11-30-2015, 02:27 PM   #15
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Rigid foam made into an angle to get to wher they need to go. If that is balloon framing, which means that the outside wall cavities are open to the attic. You need to block those first.



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