Does it make sense to add insulation to part of my attic?


I have 6" of rock wool in my attic. I'm in Portland, Oregon. About half of my 1400 square foot ranch is closed off and unheated. Much of the attic over the unheated space and part of the heated space is floored and covered with boxes of junk.
For about $200, I can double the insulation in the attic over the part that I actually live in. Sounds like a no-brainer.
BUT, I had an energy audit and they told me that If I didn't insulate ALL of the attic, including ripping out the flooring and moving all the boxes elsewhere, I'd get almost NO gain.
I'm haunted by he ghost of my thermodynamics professor saying that "that's crap!" When you insulate an area of ceiling, you get less heat loss through that area and the rest stays unchanged...but you don't lose anything. If I turn down the thermostat because the better-insulated rooms stay warmer, the rest of the house gets cooler and I should have a net gain even in the insulation-unimproved part of the house due to the lower temperature differential.
My objective is NOT to make the house warmer. It's to keep the part I live in at the same temperature using less gas.
So, do I trust an experienced energy expert or the ghost of a thermodynamics professor?
And I have the same question about insulating the floors in the inhabited part only. Thanks, mike
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Did you ask the energy audit alleged experts for the physics behind what they are saying? I agree with your assessment. If the attic is about uniformly insulated now and you only add insulation to half, you will save about half as much energy as you would if you did the whole attic. I'd like to hear the explanation for how it could make almost no difference unless you did the whole thing.
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I also agree with the thermodynamics professor.
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snipped-for-privacy@optonline.net wrote:

I never did get an actual answer to the question. I think there is some validity to the argument for floors. If you put less heat thru the floor, the underside gets colder increasing losses in the uninsulated area. I still think insulating part of the floor is a good idea.
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mike wrote: ...

There's no real difference in the floor and the ceiling -- they're both conduction problems from a warmer to a cooler region.
The underside of the flooring itself won't get cooler, it'll be slightly warmer if anything as the resistance on it's cool side goes up that'll raise the outside temperature slightly. Eventually when to the cool side of the insulation the outside temperature or basement or attic will be essentially unchanged.
--
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mike wrote:

And if you sell the house and somebody else wants to use the whole thing?
--
Blattus Slafaly ? 3 :) 7/8

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Blattus Slafaly wrote:

That's not MY problem. I'll be dead...
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I would ignore anything that guy said.
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6" rock wool is about R 22.5. R 50-60 is possibly optimal. Is your code so low as to be R 23? You will save alot insulating where you heat. What is your heat zone, for only 200 you can double it, for 400 you can tripple it. If you do rockwool it will settle alot so go alot higher.
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ransley wrote:

Well, that's another issue. Blowing it in would be nice, but I've got all that stuff up there that's not protected from lots of insulation dust. I was just gonna get the r-19 batting with the home depot rebate, roll 'em out and be done with it. Turns out that the way they have it priced, 2xR19 is cheaper than R38 and should be a lot easier to handle. Still need to look to see if I can buy it wholesale in small quantities.
I spend $550/year on heat. I've gotta be a little careful with the ROI.
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You will get some gain but heat moves to cold so it will seek an exit through the lowest insulated space.
So I guess I am agreeing with the audit guy.
That is why I always make sure to have a uniform layer even though those small cracks and odd spaces are a PITA to fill.
Colbyt
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The heat loss into the attic through the newly insulated portion will be less than what it was. Thus the temperature of the attic should become lower. This new lower attic temperature will increase the heat loss from the living space under the part of the attic that didnt get more insulation.
How much the attic temp will drop and how much extra loss from the living space is unknown but I tend to agree with the energy audit guy.
-dickm
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Most attics are well vented to the outside. Any difference in the attic temp from half the attic having 6" of insulation and another 12" is going to be negligible and not negate the value of adding insulation to part of it.
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Insulating over the livable area is where you want to add more insulation. After adding more insulation your house will stay the same temperature as before, but your A/C or furnace will work less. Don't forget to caulk and seal areas around bath fans, air returns, or pipes before insulating. Also, you may need to fasten "chimneys" to the underside of the roof for proper ventilation.
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I'd insulate the whole attic, at least what can be reached within reason perhaps with the help of a 11-16 year old kid for the tight spots (and wear breathing protection!)
I've added insulation to three different houses and every time it has made a huge difference. Rock wool sucks compared to the combination of the existing rock wool plus modern fiberglass insulation. It is like putting a big comforter over the whole house.
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