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What's best way to insulate attic against heat?


jbclem's Avatar
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02-12-06, 04:15 PM   #1  
What's best way to insulate attic against heat?

I'm replacing my living room ceiling on an old house with no attic insulation. The rafters are 29 inches apart and there is an adjacent small bedroom where I would also like to insulate the attic above it. The roof peak is about 3 feet above the ceiling.

Because of the odd rafter spacing and also cost factor (I want to do it myself) I'm wondering if fiberglass bats (or rolls) are best or if blown in insulation would be cheaper and quicker. Because this house gets very hot in the long summer months(S. California summer begins around April/May and sometimes last until October) I'm trying to figure out what thickness, or R value, insulation I should use...is it cost effective to go with the max R49?

Also, how to prevent the new insulation from blocking the soffit vents, some of which I am still in the process of creating?

Thanks in advance for all imparted wisdom and ideas.


John

 
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02-12-06, 07:06 PM   #2  
What's best way to insulate attic against heat?

You have acurately outlined your options and the limitations of fiberglass batts.

Rolls or batts are not an option for you because they limit you to the widths and thicknesses yhe pink panther makes them in. Using fiberglass, there is no way can get EFFECTIVE insulation into your structure considering the spacing and the height/access problems.

Go with blown in insulation. It will conform to your needs and give you a much more reliable insulation system. In many areas, you can rent a blower and do it yourself. You can also make it as thick as you choose.

Dick

 
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02-13-06, 02:41 AM   #3  
Dick, thanks for the answer. I like the idea of blown in insulation but I haven't figured out where to find it, and who would be renting the blower. I'm in the Los Angeles, Santa Monica area...what kind of store handles these items...are there roofing supply stores or should I be calling general type stores (Home Depot doesn't rent the blowers but I haven't tried anyone else yet).

Also, do you have a suggestion for some kind of device that would keep the insulation away from the soffit vents?

John

 
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02-13-06, 06:51 AM   #4  
They sell baffles to manage the soffit vents.

As well, you may want to consider the use of a radiant barrier on the underside of your roof. In a low humidity / high solar heat gain environment, a radiant barrier is a good idea.

 
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02-13-06, 06:09 PM   #5  
Is the radiant barrier something thin that would be attached directly to the underside of the roof? It sounds like it would be used in addition to the insulation material...what kind of difference does it make in preventing the heat from penetrating, will it boost the insulation effect by 10%, 50%??

John

 
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02-14-06, 07:07 AM   #6  
The answer to your questions is "yes"

 
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02-19-06, 01:33 AM   #7  
wflora
Lowes is the only place I've seen that rents insulation blowers.
If your house is hot in the summer, you probably need more roof vents to let the hot air out of the attic. If you have electrical in the attic, you can install a power roof vent that is hard wired and turns on and off with the thermostat it comes with. Otherwise eyebrow vents are the next best thing.

 
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02-20-06, 11:24 AM   #8  
I'm curious, in comparing adding new vents (perhaps a ridge vent) and blown-in insulation, which has the greater effect on preventing heat buildup?

John

 
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03-02-06, 03:22 PM   #9  
Additionally, does more vents increase winter heating cost?
Eg. House = 65, attic in winter = 45 (warmer than outside, colder than house).
More vents = House 65, attic 40?

 
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