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Old 03-02-2012, 06:13 AM   #1
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Would additional insulation in the attic help?


I live in south Florida where heating efficiency is not really an issue, but the A/C runs daily at least 10 months of the year. The 2-ton central air unit was replaced in 2005 and was rated at SEER 13, if I remember correctly. The house is about 1,800 sq ft with around 400 sq ft of glass in the four patio doors and nine windows. I have replaced the patio doors with French doors and I have one more window to replace. The replacement doors and windows are LowE argon-filled thermal glass that qualified for the tax rebate. I was hoping for a significant drop in my power bill, but have not really seen it.

I made a spreadsheet of monthly power usage based on daily KWH used going back to 2006. February is always the lowest month since the heat and cooling are barely used. I used this as the baseline usage excluding cooling. August is the highest usage month with about 38% of the power going to cooling. When averaged out over the year, it looks like cooling accounts for about 25% of the total power used.

I really like the French doors and windows in terms of looks, functionality and reduced noise from outside. But as noted above, I haven't seen a clear drop in my electric bill. Finally, to my question, what about the attic? The attic has about 6-8" of blown insulation. Focusing only on cooling efficiency, would I likely see any significant benefit by adding additional insulation in the attic?

BTW: The roof is a barrel tile that is attached with a polyurethane foam that should provide some insulation. When the roof had just the roofing material, the A/C would literally run day and night and struggled to cool the house. After the tiles were installed, the A/C went back to running as usual.

David

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Old 03-02-2012, 06:31 AM   #2
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Would additional insulation in the attic help?


Yes and yes.

6-8" of blown in fiberglass (that is likely what you have) is functioning at an R-Value of about R-12 when you figure in the down rating of blown in fiberglass.

Blow in some additional cellulose and you will start to see some real benefits.

Shoot for R-50 in cellulose (roughly 14")
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Old 03-02-2012, 06:44 AM   #3
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Would additional insulation in the attic help?


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Yes and yes.

6-8" of blown in fiberglass (that is likely what you have) is functioning at an R-Value of about R-12 when you figure in the down rating of blown in fiberglass.

Blow in some additional cellulose and you will start to see some real benefits.

Shoot for R-50 in cellulose (roughly 14")
Thank you for your prompt response. About 50% of the house has vaulted ceilings with only about 18" or so between the ceiling and the roof. IIRC, there may be batt insulation in those areas. The portion with 8' ceilings is easily accessible and blowing in new insulation would be fairly easy. It sounds like you suggest more blown insulation instead of a layer of batt insulation over the existing blown-in insulation. What would work best in the vaulted ceiling areas? I can get into some of the areas, but it is a close fit.
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Old 03-02-2012, 06:48 AM   #4
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Would additional insulation in the attic help?


How vaulted are those sections?
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Old 03-02-2012, 06:57 AM   #5
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Would additional insulation in the attic help?


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How vaulted are those sections?
I thought about this after I posted my comments. The vaulted sections of the ceiling are almost parallel with the roof, which has a fair, but not overly steep pitch. I would guess that batt insulation laid across the rafters would be the way to go in those areas. If so, how thick would you suggest?

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Old 03-02-2012, 07:46 AM   #6
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Would additional insulation in the attic help?


If the pitch isn't that steep, you can blow in insulation and it will not settle or sluff down if it is done properly.

The reason that I say that is because cellulose is so far preferable to fiberglass in every capacity.
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Old 03-02-2012, 08:13 AM   #7
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Would additional insulation in the attic help?


This will be a project for next winter when the temperature in the attic is bearable. It is too late for this year.

In the meantime, I had an idea. If I measured the surface temperature of the drywall ceiling at various places in the house with an infrared thermometer and compared it to the surface temperature of the interior drywall surfaces, would that give an indication of whether additional insulation is needed? That is, if the difference was small (a few degrees maybe), then more insulation would probably have little benefit. If the differential was significant, then the argument for more insulation becomes stronger. Or, is there a flaw in my thinking?

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Old 03-02-2012, 08:46 AM   #8
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Would additional insulation in the attic help?


Possibly.

Infrared thermometers pretty much useless for insulation identification.

A good visual inspection from inside the attic is probably more useful.

You might want to consider renting and IR camera for a few hours as well or get an audit done on the home.
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