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Old 07-17-2008, 01:06 PM   #1 (permalink)
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Attic insulation

To go along with adding the soffit vents I'm looking at adding some insulation to the attic of the house. It currently has 6" of fiberglass insualtion which is supposidly around an R-19. The recommended R value for my area (Wisconsin) is R-49! So, I was thinking of blowing in some cellulose on top of the fiberglass to boost it up to R-49. However, I'm also wondering if it would be worthwhile to go a bit higher than R-49? Does anyone have any info that compares added insulation to energy savings?

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Old 07-17-2008, 01:50 PM   #2 (permalink)
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I just spent about 30 minutes searching the net and didn't find much. The only actual cost benefit that I found was for the UK. A lot of other sites said to calculate it but didn't give any other information.

Nationwide Building Society - Home Energy Advice - Cost benefit guidelines

My wife and I blew 35 bags into our house -- about 10 into our interior walls (sound deadening) and 25 into our attic (extra six inches). In our area, the box stores will loan you a blower if you buy 20 bags. We divided the attic into grids so that there was a natural stopping point for hose repositioning. We used walkie talkies to communicate but couldn't use them very well through the respirators. We settled on keying the handset multiple times to tell my wife to shut off the machine. Break up the insulation as it is fed into the machine.
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Old 07-17-2008, 02:01 PM   #3 (permalink)
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I just found a site that may have a calculator but it is a gov site so it may come up with the same 48 R-value.

Insulation Fact Sheet
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Old 07-17-2008, 03:34 PM   #4 (permalink)
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Daox,
FIRST seal up your attic area: Put expanding foam along the top of wall headers, wire protrusions and such. The existing fiberglass can be your guide: It will be dirty wherever the is an air leak. I can not emphasize the sealing enough.
On attic insulation.
I would use cellulose over the top, not fiberglass. Testing shows that it just dosnt perform as rates in the cold! It looses 20% of its r value.
The fact sheet I have seen recommending R-49 from the enegystar website: Recommended Levels of Insulation : ENERGY STAR
is dated from 1997, and is based on Natural gas prices from then.
I would shoot for R-60
On Eaves: Do you hav an energy heel truss? If not, (like my house) then you should put the good stuff along the eves, the r6.5 / inch board. Reason is, that area is thin, and with celulose, you will be only able to get 3.5 inches or R3.5/inch = 12.25 at the eves.
I did this, and a boat load of sealing, and my heating (Nat gas) bill drop dramatically. They are now $50 in the winter here in Det, MI.
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Old 07-17-2008, 04:18 PM   #5 (permalink)
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Thanks for the suggestions guys.

I was actually reading up on that site a little earlier today truckncycle.

Larryrose11, its great to hear your heating bill is that low! My goal is to keep utilities under $100/mo average.

I had planned on sealing up the attic, although I haven't thought as much about that yet. It sounds simple enough. Can you recommend any specific product to use as far as expanding foam? I know there is Great Stuff, but thats about all I know of. I definitly plan on using cellulose instead of fiberglass. Just the thought of installing blown in fiberglass makes me itchy.

I'm not sure what I have as far as trusses go. I can pretty much bet its no energy heel though. The house was built in 1886. I'll have to take a look and see what can be done. How far in did you go with the polyiso insulation?
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Old 07-17-2008, 06:39 PM   #6 (permalink)
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I have blown Cellulose in my camp works very well, is affordable, easy to install, is flame retardant and most of all, I just like the stuff.

and a DreMD top Tip if your walls aren't insulated (most of mine arn't). You can cut a small hole (1" worked at camp) and blow cellulose in. I strategically drilled holes in places that would be covered with pictures, moulding, used some outlets, installed 2 blank outlet plates. All and all made the place much more comfortable (rarely ever have the A/C on over there).
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Old 07-17-2008, 09:18 PM   #7 (permalink)
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Daox,
My goal was to have R-35 of cellulose at the transition between the cellulose and the polyurethane foam, so that is 10 in thick. How far back from the wall header depends on your roof pitch. Mine is pretty shalow, a 3:1 pitch. The final block design was shaped like a wedge with the nose cut off with 2 small 1/2 inch strips along the sloping face to create an air chanel. I squirted a heathy dose of Great Stuff Foam on the top of the exterior wall header when I installed it. It works great. NO icicles anywherte, and a thermal scan showed no cold spots. It was a pain to install, but I kinda overdo things when I never want to go back to a spot in the house. An easier solution is to contact a polyurethane spray foam installer and have they do your attic in the trouble spots, like wall headers, recessed lights, and the eves. It will be cheaper for a pro to install the spray foam than the DIY approach because of the HUGE markup for the DIY kits, like Tigerfoam. I went with a pro installer when I did my exterior remodel, because his quote came in under the DIY material cost
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Old 07-17-2008, 10:12 PM   #8 (permalink)
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Here is a pic of our exterior remodel, or at least the insulation layers. On the front is the 2.5 lb per cubic foot, 3 inch thick polyurethane spray foam in the stud cavity, and on the side you can see the 1 inch foam decking that is covering the spray foam. Overkill perhaps, but there are health issues in the house with mildew, which drove this solution. The foam contractors also installed a plug of foam above the wall header at the eves, and filed the joust cavity in the basement where the house meets the foundation. There is a fresh or make up air inlet in the basement with a sealing air valve that opens on air pressure. The furnace gas solenoid also drives a relay, turning on a small (80 CFM) exhaust fan insuring fresh air in the house in the winter. My heating bill would be lower If I had a high efficiency furnace, but I don't. The furnace is original 1963 equipment and in good shape. High efficiency furnace without good insulation just efficiently wastes heat.
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Old 07-18-2008, 09:41 AM   #9 (permalink)
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Sounds like a very nice setup. What is the R-value of your walls?

While searching today I found almost exactly what you had posted before:


BTW, do you recall how much a 1" thick polyiso sheet costs?
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Old 07-18-2008, 10:29 AM   #10 (permalink)
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The r value of my wall is 28. I have 39 in my attic now, I will have R-60 this fall.

Sheet foam cost? I believe that they were about $12 per 4x8 sheet.

The diagram is similar to my house, but I have no soffit vent. I had an ventilated drip edge installed with the exterior remodel, which provides me the ventilation I need up there. The difference is that I went overboard, and where diagram has fiber insulation, I still have more board there. I love foam board.

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