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Should I Put in More Attic Insulation?

Post in 'The Green Room' started by velvetfoot, Aug 29, 2006.

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  1. velvetfoot

    velvetfoot Minister of Fire

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    It has R38 fiberglass batts now. Outside temps are getting cooler - attic enviro (1000 ft2) might start to get tolerable.
    Oil is getting so incredibly high, economics might be different than they were just a short time ago.
    Thanks.

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  2. Greg123

    Greg123 New Member

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    The recommended R Value for New York Region is R49 it wouldn't hurt to add more to your existing R38
  3. Rhone

    Rhone Minister of Fire

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    I have a program that calculates this. For Sand Lake, NY with 6,757 heating degree days and 598 cooling going from R38 to R49 will save you 9.12 gallons of oil per year, and 24.8 killowatts/year in electricity for cooling. How much do you pay per gallon of oil, and per kilowatt and you'll figure out your money is probably better spent elsewhere. First, it's not easy to add insulation to R38 because you've already covered the joists. You'll have to remove and replace as you go. Any insulation you add up there will let you claim 10% federal tax credit on material costs so that will help, but even with it adding another R11 fiberglass looks like a 5+ year payback. Anything over 5 years is deemed an unwise decision unless you plan on staying there a long time. Blown cellulose is a possibility to get you to R49, but you'll be doing a lot of work and have to pay for renting the machine, and most likely have to buy and install the soffit ventilation jackets so the blown insulation doesn't suffocate your attic ventilation. That's a pain now that your insulation is already R38.

    I have to say not worth it for 9.12 gallons of oil and 24.8 killowatts/year in electricity based on the amount of work, price, and difficulty and you're already preventing the "short circuiting" of the joists with your current insulation levels. Even adjusting for oil increasing 15% compounded each year the amount of years to reach payback still doesn't look worth it. I recommend you spend the money instead on an energy auditor to come and analyze your house and request one with a thermal imager, your power company may give you a discount or provide an auditor for free but that's usually if you heat with electricity. Energy auditors are money well spent particularly when your house is buttoned up.

    I should explain that the main reason is because your heat loss is halved each time your insulation doubles. So, starting with R38 you'd need to add another R38 making it a whopping R76 in order to cut your heat loss in half through your attic. So, adding R11 to R38 isn't going to do much. However, if you were starting with R6 simply adding another R6 to it cuts your heat loss in half, can you imagine adding R11 to something that's R6? That would cut your heat loss by 71%! So, you want to focus on the items that have the lowest R-Value.
  4. velvetfoot

    velvetfoot Minister of Fire

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    Thanks for the thorough reply. I hate going up there in the attic anyway!!!!
  5. elkimmeg

    elkimmeg Guest

    How is your attic access insulated. Did you know thar there is a insulated box withweather strippind an held into place with velcro fasteners. Attic access is a huge hole in your insulation envelope. What about weather stripping your cellar door? Have you installed insulated plug and switch insulators behind every outside wall outlet. What about applying weather stripping to the sills of your windows. BTW how draft resistant are they what is there U vlaue. How well is you wood seal and foundation contact?
    notorious for leakage. Have you insulated your pipes and ducts and to what r-value/ What about duct sealing all your duct joints first.
    Attic exchangers/ furnaces loose 35% of the heat in transmission what about duct seal and better insulation there? What about high low wall registers in upstairs rooms? Point being there is a lot of areas for improvement the adding R11 to you attic to save 9 gallons of oil..

    I often wonder about people that buy supplemental heating appliance, when money is better spent keeping in the heat generated and holding out cold air intrusions. So many ways to improve our current situations hot water tank insulation pipe /duct insulation.
  6. velvetfoot

    velvetfoot Minister of Fire

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    Good suggestions all!
  7. wg_bent

    wg_bent Minister of Fire

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    Seems a long way off....the heating season. I'm in Austin today...93 today, expected to be 101 tomorrow.

    Elk's right on with the "Find the weakest link" points. I began looking at my crawl space and basement this year, and I'm sure I'll improve the efficiency of the house by leaps and bounds with the efforts underway. Last year I started my campaign of improved efficiency after the stove was installed, and I found all the ones Elk pointed out. Switch plates were so leaky there was wind blowing in, the attic access was nothing but a peice of fiberglass stuffed in a hole in a closet, and probably the worst was the attic fan that had no insulation layer at all over it. There were a bunch of others too, but they all got plugged, and the house seemed to get more comfortable immediately. Actually measurable in one case.

    Given the analysis that Rhone gave, I'd say become very critical of all the small stuff in the house like Elk and I mentioned and you'll find some stuff that's easy to fix and makes a big difference.
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