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Reinsulating Attic from Scratch - Multiple Questions


Cerestes's Avatar
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Join Date: Apr 2005
Posts: 117

09-01-05, 02:00 PM   #1  
Reinsulating Attic from Scratch - Multiple Questions

Going to be removing all old (blown fiberglass) insulation from the attic a 1969 house.

For the new insulation, our plan is to use fiberglass bats, for a total of R38 to ~R40.

Now the main question -- Our attic was built using 2x6's.
We can either install using a single layer of R38. My concern is that this leaves strips of non-insulated spaces directly over the joists every 18 inches.

Second option would be to use a layer of R19 or R21 between each joist, and then run another layer of R19 or R21 perpindicular to the first layer.

Any ideas which method is preferred solely from an insulation perspective?
I realize doing it with two layers is essentially twice the work. Not an issue if its a better result.

What about cost? I can't find insulation for sale online to get good cost estimates. How much does materials alone cost for R19, R21, and R38 in rough squarefootage prices?

 
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Concretemasonry's Avatar
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Join Date: Mar 2005
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09-01-05, 02:37 PM   #2  
Reinsulating Attic from Scratch - Multiple Questions

If possible cover the joists. You have better insulation.

Even if the joists are wood, they still are a "thermal short-circuit". You are lucky they are not steel (30- 0% reduction in R-value).

Dick

 
Cerestes's Avatar
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Join Date: Apr 2005
Posts: 117

09-01-05, 07:47 PM   #3  
So in short, 2 batts of a theoretical R16, is better than one bat of R32, because the perpindicular batt will cover the joists?

Alright, now anyone know where to buy insulation online? (Or more importantly, at least get good price estimates based on square footage?)

 
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