Insulation: Blown In or Behind the Siding?

I'm in a house that's new (to me), and it's downright chilly. The house could use (but doesn't necessarily need) new siding, which would provide an opportunity to install those sheets of insulation underneath. I don't like the siding color, so this would achieve two purposes. But, this year, the budget would not allow for both siding, and blown-in insulation. Anyone know how the two methods (exterior sheets vs blown-in) compare, in terms of slowing heat loss?
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I would think that if you are going to drill holes in the outside walls to blow in insulation that the time to do it is when you are doing the siding. Wait till next year if you have to.
More importly, why is your house so chilly? Could there be another reason like inadequate attic insulation or drafts? My reasoning being that my house has no wall insulation (bricks -> cinderblocks -> plaster), but I have an attic full of insulation and double pane windows and no drafts, and it's really OK like that.
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All windows except two have storms, and tight ones, but with only an inch between the panes. There's a large on in the living room that's single pane, and another in the kitchen. I've put plastic on them for now, almost 6" in from the glass. The attic's got 12" of the pink stuff. I've been gradually prying open outlets and other access points, but I still can't get a sense of how much insulation's in the walls. Doors are tight.
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"Doug Kanter"

This one is easy - get the R value of whatever particular product you are looking at. Sheets will generally be much less than blown in insulation. As another poster mentioned, it will likely be a world easier to blow it in from the outside, where you can just cork the hole and put siding over it - vs redoing perhaps 1-200 holes all over inside the house in your sheetrock.
I have 1/2" insulation under steel siding, with no insulation in the walls. The siding thing helps, but there is still a definite temperature gradient you can feel inside the house in the hottest of summer and coldest of winter days. I have ceiling fans in every room now as well as a whole house fan, which made a big difference in overall comfort. Colorado. I'll likely never blow anything into the walls. Sounds like an epic. I have trouble seeing how it would pay off in less than 10-15 years.
- Nate
-
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1/2' white foamboard is R 1.75 The pink it is R2.5 for 1/2" . Blown in at 3.5 inches will be alot better. But what will you use Cellulose ? It can make your house a mess with future dust. Icynene foam would be the way to go 3.5" of foam would be R 12.25
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http://www.cocooninsulation.com/existinghome-insulationcomparison.asp?Type=H
Cellulose is better at soundproofing and reducing air infiltration
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http://oee.nrcan.gc.ca/keep_heat_in/index.cfm
Cellulose would be my choice as it is 1/3 the cost of the rigid sheets but I also plan on airsealing every crack to eliminate any dust or air infiltration.
BTW, if you are in Canada the government will provide a grant based on the difference pre/post retrofit energy improvements done to your home. I just had my 'pre' test done and have the potential to go from a energuide rating of 37 to 77 which will result in a rebate of $2100.
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Depends on what your siding is. Mine was wood which I removed, removed 50 year old tarpaper, put in 4" insulation and recovered house in tyveck then put wood back up then vinyl. Lots of work (mostly for my 15 year old son) and done in sections. Works fine. stan

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