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Old 12-08-2015, 01:12 PM   #1
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Adding more blow-in insulation to Attic - Advice needed


I live in Northern Virginia and I'm hoping to add more insulation to my attic.

I'm not sure whether I should use cellulose or fiberglass, since it looks like I already have about 6"?? of fiberglass. Can anyone confirm that this is fiberglass?




Is it best to use the same material? How much more insulation should I add? Would achieving R50 be a waste of money?

Any tips or advice is greatly appreciated.
Thank you!

Last edited by jr64; 12-08-2015 at 01:15 PM.
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Old 12-08-2015, 01:48 PM   #2
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The 2009 energy codes are showing R-38 for all of Virginia. You can of course add more, but the rewards will be less. Your picture shows at least the 6" mentioned so adding another 5 or 6 inches should meet current requirements.

However, will that be cost effective? If you assume your ceiling is 20% of your overall energy costs (heating and cooling) and you double your ceiling insulation, you will reduce the energy loss from that area by 50%. If you currently spend $1,200 per year on related energy (omit lights, cooking, and hot water, 20% of that would be $240 per year. Save half of that and you save $120 per year or an average of $10 per month.

I'm not trying to discourage you from making improvements, just putting this one into perspective. There are several other areas where improvements can also be made and it is the sum of all of them that creates the rewards and some of them are easier and less expensive.

Your first objective should be to identify all areas where savings can be made and then organize those by cost and what should be done first. Adding more insulation now would make any air sealing up there more difficult if not impossible.

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Old 12-08-2015, 02:25 PM   #3
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Heat flow vs. insulation value is not a linear relationship so you won't (in theory) double it save 50%.

The bigger improvement in your case would be via a better (denser) insulation. Blown in fiberglass is cheap and so lightweight that it allow convection to happen inside of it.

Here is a good post from a regular contributor (Gary) here on fiberglass.

http://www.diychatroom.com/f98/bigge...ulation-90438/

Long and short of it is that you are only realizing about 50% of your installed R-Value with fiberglass.

Blow in a cellulose cap over the top, after you air seal, and then you are are good.
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Old 12-08-2015, 02:34 PM   #4
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Assuming you are paying cash, even the most dismal ROI is better than than the .10% you are earning on your savings.

Stay with the same materials.
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Old 12-08-2015, 03:17 PM   #5
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W/W you are of course correct, I was just trying to provide an easy explanation, which yields poor enough results. I also want the op to consider looking around the house for more rewarding improvements. As you know, attics and windows are often the first choice for improvements with perhaps some of the least rewards.

Corrections always accepted,
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Old 12-08-2015, 03:42 PM   #6
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Quote:
Originally Posted by Bud9051 View Post
W/W you are of course correct, I was just trying to provide an easy explanation, which yields poor enough results. I also want the op to consider looking around the house for more rewarding improvements. As you know, attics and windows are often the first choice for improvements with perhaps some of the least rewards.

Corrections always accepted,
Bud
No corrections required Bud.

Notice I said "in theory". The poster will save something and it will be decent as long as they combine it with some air sealing.

That 6" or so of blown in fiberglass is working about like an R-10 so more is going to be more in this case.

Get that attic air sealed and and then insulate with blown in cellulose and the home will tighten up nicely.

I haven't been in a home yet (unless purpose built for tightness) that didn't benefit from air sealing and insulation. Sure isn't sexy on the scale of home improvements but it does work.
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Old 12-09-2015, 06:51 AM   #7
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Thank you for all your responses.

In the OP you can see the top of a joist (where someone walked) which I believe is 2x6" so my current 6" of insulation is on the conservative side.

To clarify it's best to go for atleast R38 with cellulose (even though it costs more per bail) with my current layer of 6-10" of fiberglass. But it's more important to seal around ceiling penetrations prior to insulating. Correct?

What's the best way of sealing around penetrations with the 6-10" of insulation already in the way?

Also what are other ways of energy savings for a home. Since I don't want to rip out walls and I can't see how to improve my windows. The home is 2002 with double pane vinyl windows. I do feel small amounts of cold air coming through the cracks in the window. However, I feel if I seal these then the window will be inoperable.

Last edited by jr64; 12-09-2015 at 06:57 AM.
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Old 12-09-2015, 07:23 AM   #8
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The first question I ask when someone wants to reduce their heating and cooling costs is, what are you spending now. A 2002 home in VA shouldn't be burning through energy like one in the far north, so give us a reference, total electric and gas bills for one year (roughly is fine).

All windows will leak a little, either where they open and close or around the frame. If you turn on all exhaust fans, bath, kitchen, and dryer, then test around the windows you might locate the source. Recognize all cold windows will have cold air flowing down off of them, convection.

To access the attic floor for air sealing a rake may work best to fluff the current insulation out of the way. But, if you target known problem areas you can avoid rearranging the entire attic. Here is a link that may help.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

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Old 12-09-2015, 07:38 AM   #9
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The home is 4000SF
5 bedroom 3.5 bathroom, open plan
3 levels including fully furnished walk out (at grade) basement (with 1b and 1ba)

Approx. cost per year for Gas Heat - $822
Approx. cost per year for Elec for A/C - $510

-I'll try the window test.

-I don't think we have any problem areas in the attic and looking at some websites our joists might be 8" and we might have 8-15" of blown in fiberglass.
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Old 12-09-2015, 07:59 AM   #10
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Quote:
Originally Posted by jr64 View Post

Approx. cost per year for Gas Heat - $822
Approx. cost per year for Elec for A/C - $510
That does not sound too bad to me.

Your rates may be different. MCF per year might be a better number to provide. It may be stated on your gas bill.

Hot water is gas or electric? Range? Dryer?
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Old 12-09-2015, 08:10 AM   #11
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Dryer is electric
Range is gas
Water heater is gas

I accounted for the normal Elec usage during winter $54/month
and the normal gas usage during summer $22/month

for example our annual gas bill would be 22*12+822 listed in my previous post
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Old 12-09-2015, 08:15 AM   #12
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Can anyone confirm this is blown- in Fiberglass and not Rock wool or some other product??

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Old 12-09-2015, 08:39 AM   #13
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Its blown in fiberglass.
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Old 12-09-2015, 10:34 AM   #14
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Your gas bill for hot water and cooking in the summer may be $22 per month, but I suspect you heat more and colder water in the winter. I also suspect you cook and bake more in the winter.

We use an MCF or less per month in the summer to heat 50 gallons of water for two people and dry our clothes. The average input temperature of the water is close to 50-55 degrees. That input temp drops a good bit when it gets cold outside. Family size affects hot water usage both for baths and clothes.

$1086 per year for
Quote:
The home is 4000SF
5 bedroom 3.5 bathroom, open plan
3 levels including fully furnished walk out (at grade) basement (with 1b and 1ba)
is not bad at all. We have 2600, 2 levels, partially open floor plan, with unfinished and unheated basement. We use slightly over 100 MCF per year or about $1000 at current gas rates. 2 gas furnaces @ 80%, gas water heater and gas clothes dryer. Central KY, USDA zone 6 if you want to compare temps.

I'm not saying more insulation is wrong. I will probably have some more blown in myself but you aren't all that out of line.
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Old 12-09-2015, 01:58 PM   #15
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Informative reply. Thank you.

Yes, we have 3 adults and a baby. Someone's renting the basement and paying half the mortgage.

I was under the impression that we needed more blow-in but after reading the responses seems like more would be nice but not necessary for efficiency. Instead of putting more insulation in think I am going to:

-fluff the flattened areas
-even out any mounds
-take measurements across the entire attic space so I know exactly what's lacking
-test for air seeping through the ceiling and possibly sealing up any problem areas

Maybe after all that I will determine if I will benefit from another 6" or so of insulation (cellulose this time).
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