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I have a 6 year old home with about 12 inches (R-30) of blown-in insulation in the attic. Recently door-to-door sales representatives for an insulation company offered a free inspection and quote to add additional insulation. The pitch was that the R-value at the time of construction was sufficient, but that codes have been revised and more insulation is better.

I was provided with options for adding 8 or 12 more inches to attain R-49 or R-60 respectively.

Sure, insulation materials improve with technology, but should I agree to have additional insulation put in? Will adding more somehow pay for itself? Is there such a thing as too much?

I live in a desert climate with temperatures ranging from -20°C (-5°F) in winter to 32°C (90°F) in summer.

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My policy is to never buy from anyone coming unsolicited to your house. Their "free" inspection will always find a fault which miraculously they can rectify. Say no and if you think you want to proceed get at least two more quotes so you can compare prices. –  ChrisF Jan 28 '11 at 12:09
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And if you're really lucky, they'll damage your home to create things they can fix. Unsolicited home improvement tends to be very bad. –  Scivitri Jan 28 '11 at 18:01
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In my neck of the woods, it is hard to even get an appointment with a good energy/insulation contractor. With the federal and state rebates and tax credits, they are high demand. Can't see why anyone reputable would be going door to door. Caveat Emptor. –  shirlock homes Jan 28 '11 at 21:20
    
The law of diminishing returns tells me that R49 isn't much better than R39 and R60 probably even more so. For hot summer roof problems, power vents and radiant heat control are more important once you've reached R39/R42. –  Fiasco Labs Oct 24 '12 at 6:38
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I have about 6 inches of blown-in insulation in my attic. When the temperature is 30 degrees, I have frost on my roof. That tells me my insulation is adequate. Thus more insulation would have a very long payback time. Since the "experts" think I should have at least twice this amount of insulation, what am I missing? –  Les Oct 24 '12 at 14:10
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4 Answers

up vote 37 down vote accepted

Good question. First off, there is no "code" requirement that would mandate adding insulation to a 6 year old house. The current standard in new construction is to try to achieve a R-42 in attic spaces. Adding more insulation to your R30 is not a bad idea, however I have a few questions for you. What kind of insulation do you currently have installed there now? What are the dimensions of the space and style of house and source of heat and A/C.

Adding more insulation is almost always a good long term investment, but before I would trust a sales pitch from a door to door vendor, I would investigate alternate routes. If a DIY project, costs to simply add a layer of R 13 or R19/23 fiber glass blanket over my existing insulation.(assuming it is also F/G blanket style). I would also seek quotes from a couple of reputable energy conservation/insulation contractors in your area. A good contractor will ask you the same questions I have, and ask about your energy costs now, then calculate the potential energy reductions in hard numbers or percentages and expected pay back period. Some energy audits are offered at a reasonable fee or even free and address several aspects of comprehensive energy savings in the home. It can be amazing what a little caulking, joist/wrap box insulation, weather stripping, hot water conservation methods and increased attic insulation can make in your total energy picture. Does your state require a professional license or certification for this kind of work? Be cautious and seek a trusted professional opinion.

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Thanks for the excellent answer. To address your questions: The insulation is blown-in, and according to my quotation, of "F/G" type. The home is a split level 1500 sq. ft. with central heat natural gas furnace and A/C. –  JYelton Jan 30 '11 at 18:20
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Normally, blanket type is not laid over blown in. usually more blown in is used. –  shirlock homes Jan 30 '11 at 20:41
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OP, in your case adding insulation to bring the average up to r 38-40 is a good idea. At 1500' feet you will notice a lower energy bill. How much? Tough to say since I'm not there to see it. You will gain a greater improvement in the ceiling then what you would by changing windows even. It's probably the most cost effective way to lower your costs.

Over 38 it starts to not do much. Never batt over blow. I prefer batt 19 and blown 19 over the batt myself.

Air infiltration around outlets, top and bottom plate penetrations and weather stripping do make a big difference for very little.

Radiant barrier is nice if you can get to it with existing construction. If you chose this, obviously do it first before retouching blow.

Last, if you have cellulose, fiberglass above is ok, never let anyone blow cellulose over fiberglass. Batts or blown.

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US Department of Energy recommendations are R-49 to R-60 for 85 percent of the country. The best source of info would be the Department of Energy website. Make sure your contractor air-seals the home too, or else you aren't doing anything.

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R-value is not a good metric of real world insulatitive capabilities as it fails to account for air flow, heat emission, and moisture.

With respect to airflow and moisture, this why a wind-breaker can keep you warmer on a windy or rainy day than a sweater can, or why a thermos will keep our soup warmer than 6" of cellulose fill (especially if you were use a solid lid vs a lid made out of cellulose fill)

This means a thin layer of spray-foam insulation could actually do more for you than a thick layer of batt.

If you have batt or blow insulation that's in good condition, it is likely that the best thing you can do increase your energy efficiency is to seal airflow!!

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You're absolutely right that sealing the leaks between the living space and the attic is essential, but -1 for hyberbole of "almost useless". –  littleturtle Feb 5 at 15:49
    
@littleturtle agreed and fixed; sorry about that, the hyperbole got carried over from an article I was reading –  virtualxtc Feb 5 at 19:14
    
It is still not correct to say that R-value is not a good measure of insulation or that it doesn't measure convection. See: greenbuildingadvisor.com/blogs/dept/musings/… –  littleturtle Feb 25 at 22:44
    
@littleturtle you link is pay-walled, but I decided to clarify my convection statement a bit as indeed R-value is suppose to account for small scale convection, but it doesn't account for the larger convective forces that occur in an attic. –  virtualxtc Feb 26 at 9:31
    
@littleturtle your link is pay-walled so I couldn't follow it -- indeed R-value is suppose to account for small scale convection, but it doesn't account for the larger convective forces that occur in an attic. That said I can lump larger convective forces is similar enough to airflow, that I can just remove it without damaging my answer. –  virtualxtc Feb 26 at 9:41
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