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I noticed my attic blown in insulation is rather thin on one side. Rather than buying enough to cover the whole area, I was thinking of just pushing or brooming the blown in insulation toward the soffit to fill it to the top of the joists, and then laying some batts into the cleared space.

Is there any reason I shouldn't do that?

EDIT: Please note: Adding more blown in insulation is NOT an option and I wish people would quit mentioning it. I KNOW the differences. I want to know if there are any TECHNICAL REASONS why I don't want to do this ONLY!

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  • I like the fiber glass to the soffit 4ft batts because stays out of soffit vents.. If you had small leak easy to remove and replace.. I do not see any Technical Reason you can not do that.But insulation has compacted when you rake stirs up again later on may want to check and see if you need a little more .. – user101687 May 27 '19 at 23:47
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Cellulose (the typical, but not the only, blown in) is much less air-permeable than fiberglass. Some tests even show it works without a vapor barrier, though I certainly put one in anyway on my project using it. It also has an R-value that increases in the cold, and no seams.

Fibreglass batts are considerably more air-permeable, have seams, and have an R-value that reduces with cold temperatures - which is not great if insulating to reduce heating costs.

So: doing what you describe is both possible and better than doing nothing, but inferior to (and probably more expensive than) blowing in more cellulose. If you have a near-religious objection to more blown in, by all means level out the blown-in and add fibreglass batts, rather than not adding anything. If, (as seems unlikely from your comments) you'd like the best insulation job for your money, consider adding more blown in.

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  • Bit late, but blown insulation probably has fixed overhead costs that only make sense once you reach a certain scale. Does OP have to rent a blower to install it? If so, then a roll or two of R-19 insulation is probably cheaper. – TylerH Nov 30 '20 at 22:21
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The recommendations for R-values in attics has increased. Since your insulation doesn't come up to the top of the framing I'm guessing where it's not low it only comes up to the top of the framing. That means even if you had the insulation to the top of 2x6 joists you'd be below the new minimum recommendation.

Blowing insulation is usually easier and cheaper than laying batts. You may even find someone to do it for you for less than the cost to buy batts.

If you're going to the trouble I think you might as well consider adding enough insulation to meet the new recommended minimum. Then just add more blown in insulation. You'll save a lot of time compared to sweeping the old and then spending all that time on your knees in an attic cutting and installing batts. Probably save money to and get a more energy efficient attic.

You can rent a blower and I think if you buy a certain number of bags some of the big box stores will include the blower rental for free.

I'm looking into blowing in insulation over my existing batts because it's going to be cheaper than adding an additional layer of rolls.

Update: You didn't indicate the size of your attic or how many square feet you have that needs added insulation.

If you only have a small area to do such that renting a blower is cost prohibitive (less than 10 bags so no free blower rental) or a PITA you can always apply the blown in insulation without a blower. It's easy to break up by hand and sprinkle it over the area then rake it smooth. You can also drop chunks of the insulation into a clean, empty trash can (maybe 5 gallon bucket if you can't get trash can up in attic) and break/fluff it up with a paddle mixer on a drill then pour it out into the area.

Either way I look at it, adding more loose fill seems to save steps, time and money.

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    In no way does this answer my question. – Rob Dec 15 '13 at 19:24
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    @Rob The last question was "Is there any reason I shouldn't do that?" I think my answer is a valid reason not to do what he suggested. It's cheaper and easier to add more blown in insulation. – OrganicLawnDIY Dec 15 '13 at 19:26
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    I'm asking if there's a reason why I don't want to sweep it aside and add batts, not whether I should add more insulation or a different type. – Rob Dec 15 '13 at 20:14
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    You don't have to add more if you don't want to but I think it's a good idea. I updated my answer to account for a smaller job. Unless you left something else out I don't see any benefit to sweeping the existing insulation off to the side and replacing it with batts. Only downsides. Is there any reason you're contemplating doing this instead of just adding more loose fill to what you have? – OrganicLawnDIY Dec 15 '13 at 20:28
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    Well, you might be right, but it has nothing to do with the question I asked. – Rob Dec 15 '13 at 21:12
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One of the problems with blown in insulation in new homes is that you have sub-contractors that just don't care whether they do it right or not. About 6 years after living in our new house, I crawled back to an area over our master bathroom and master closet to find that I had only about 2 inches of insulation in many places and could almost see the drywall of the ceiling in others. I gently raked out the blown insulation, one small area at a time and put in R30 batt insulation. Then raked the blown insulation back over. Before that I had wondered why the bathroom seemed so cold.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know how best to contribute here. – Daniel Griscom Dec 11 '19 at 11:56

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