During the recent removal of the unused chimney, I noticed that the previous owners of my house had done some “work” in the attic which compressed the blown-in insulation. It appears that some of it has been pushed out of the way, but most seems to be compressed down between the ceiling joists. First attempts at just trying to fluff it up does not seem to get the results. The insulation looks rather thin at that point and the R value would not be what I’d expect. Should I remove the compressed insulation, toss it on top of the good, and then blow in new? Is there a preferred method to correct this?
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Replies
The compressed insulation will perform better than if it were fluffy. Leave it alone, or pile more on.
NOT TRUE, just the oposite
When insulation is compressed it loses some of its R value.
Is it fibreglass, mineral wool or cellulose?
It's fiberglass. There is a path down the center of the attic that has the top 6 inches of insulation, above the joists, that appears to have been compressed by either some one crawling across the attic, or laying a piece of plywood across the joists. There was no plywood up there, plus it looks like the insulation is not uniformly compressed.
I thought that fiberglass insulation looses some of it's R-value when it get's packed too tightly. Is that just for batts, or does it apply to blown-in also?
I would think that compressed fibreglass of any kind does lose some r value. Less trapped air?
Dump out some bags of cellulose insulation in the low compressed area. Loosen up the clumps in teh cells as you dump.
In my own attic, straight down the middle (over a load bearing wall) I built a "cat walk" 14 inches higher than the ceiling joist tops. Had cellulose blown in all over to teh bottom of the "walk". Lets me get around up there w/o getting all filthy nor disturbing the insulation.
You are correct in assuming that compressed insulation loses some of its R value.
More density blocks convective currents better.
Adding more on top would be better than 'fluffing' what is there.
Is this the case even with cellulose? I had "dense pack" cellulose blown in and they claimed they gave me an R-30 (or was it R-38--have to check my receipt) in a 9" space. I know "regular" cellulose blown in, an R-38 is about 14" or something.
Cellulose fibre has a R value of 3.4 per inch.
Also, there is a great difference in an R value if the insulation is blown in and left alone to weight form from its own density, or is subjected to working or stomping on it; therefore the compressed problem.
"compressed" or "stomped" on are two different factors.
I have a subfloor for storage in my attic. I was told by a contractor that he could dense-pack with cells under the floor boards and get about R-5 per inch.