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Incompletely adding insulation to attic floor - worth it?


xvimbi's Avatar
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02-14-10, 05:38 AM   #1  
Incompletely adding insulation to attic floor - worth it?

Our attic has about 8" of blown-in fiberglass. The job wasn't done that well; one can see heaps of the material in some spots, large amounts sticking to trusses, etc., so nobody cared to even it out.

In any case, Home Depot sells R-30 unfaced fiberglass batts ~$0.30/sq.ft. right now, and so I was thinking of augmenting the attic insulation. However, there are some areas where I won't be able to add additional insulation: OSBs have been put over the central attic portion, about 1/3 of the main attic floor space. I could probably raise part of it to add the additional insulation underneath, but the heat pump rests on it as well, and I don't feel comfortable to raise that one. Also, the portion over the bonus room would require a remote-controlled vehicle to get to. It will probably have to stay the way it is.

Despite these issues, would it still be worth to put the additional insulation in?

Bud, if you see this thread, you don't have to say it: I will of course take the opportunity to go through everything and stuff as many holes as I possibly can

Is $0.30/sq.ft. actually a good price, or can fiberglass batts be had cheaper at contractors' sources?

Thanks so much! MM

 
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Bud9051's Avatar
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ME

02-14-10, 06:34 AM   #2  
$.30 is a good price. Insulating what you can certainly helps. The chart in this link illustrates that the first few inches are the most important. http://www.anchorinsulation.com/pdfs...insulation.pdf
Adding more and more helps you get those last few BTU's when they are real expensive.

For the area you can't easily reach, it may help to build a long pitch fork. I put a "T" on the end of a piece of strapping, no knots, and drill some holes and install some 3" nails. This allows me to fold a piece of insulation over the end and slide it into areas I can't reach, then position it as best possible. It won't be perfect, but again, the areas you can cover add to the overall average R-value.

Glad you are reading.

Bud

 
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02-14-10, 07:37 AM   #3  
Thanks for the quick reply. The rake idea is good, but I would need a 50-ft rake...

Also, I have seen those graphs you linked to before and was a bit puzzled. They essentially show that additional insulation would not result in a reduction in heating or cooling costs. Now, I realize that pamphlet is from the manufacturer of Icynene, so it should probably be taken with a grain of salt. And it's certainly not quite in line with what most other sources say.

Am I looking at the data the wrong way?

MM

 
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02-14-10, 09:30 AM   #4  
Actually it is correct. The first few inches do most of the work, but even the remaining 1% or 2 % can cost a lot. The irony in the insulation business is that the recommended amount of insulation is based upon the cost of energy. Will that extra 6" of insulation save enough money to justify the costs. Well, I ask, what is the current price of energy and if I install it myself shouldn't I put in more. The answer is, we will pay dearly for tomorrows energy and if I'm up there installing this stuff, I'd rather do more now than have to come back. But the diminishing returns are correct. 12 inches of insulation with 2% loss would have to be increased to 24" just to get to 1% loss. (approximately) That's where the bean counters come in, to tell you if that extra insulation is a good investment or not.

Hope that helps, and you are correct to be watchful of advertisements .

Bud

 
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02-17-10, 08:55 AM   #5  
I've got a couple of questions regarding the insulation work.

Bud, could you (or the o.p.) snake the insulation
blower hose under the floor, and drag it out as it
fills in the space ? sort of a wall fill on it's side.

MM the 50' rake, when I was doing my attic fill
a couple of weeks ago, I rigged up a 3' long piece
of 2" pvc pipe on the end of the hose for the operator,
and he told me (I was tending the machine outside) that
the velocity was quite high, and he didn't even need
the other pipe I made up (a 7' long oneI made for reaching
into the eaves).

I also put a second blower inline, for more "push"
and he commented he could have done the whole
24' square attic by sitting in one corner.

 
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02-17-10, 09:12 AM   #6  
The 50' rake was referring to a long pole to push batt insulation into place where it is too narrow for human beings.

Yes, there are many ways to get blown insulation to where you want it, but it is important to spray it in a manner that packs it tight, thus the term "dense pack". Projecting it across 24 feet of attic would not accomplish that . I'm sure you know that, but need to be sure all others who read these threads understand.

Bud

 
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02-18-10, 07:15 AM   #7  
Posted By: Bud9051 The 50' rake was referring to a long pole to push batt insulation into place where it is too narrow for human beings.

Yes, there are many ways to get blown insulation to where you want it, but it is important to spray it in a manner that packs it tight, thus the term "dense pack". Projecting it across 24 feet of attic would not accomplish that . I'm sure you know that, but need to be sure all others who read these threads understand.

Bud

Bud,
I always thought dense pack was for the walls, the attic
fill was always just a "throw it in there" kind of operation.

50' rake, yes I assumed for fiberglass batts, that's why I suggested cellulose instead, the ability to get material
where you cannot be (don't have to right on top of it, using
staple gun).
tnx
Doug

 
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