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Old 09-09-2015, 10:02 AM   #1
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Blown Insulation Thickness


Location: South Florida (Boynton Beach)
House: Built 1947, 1400sf, single story, new asphalt shingle roof, concrete block construction, old original fiberglass bats in attic, worn and missing areas, lots of gaps, several square feet with no insulation.

I'm having a terrible time finding out just how deep a layer of blown cellulose insulation I should put in the attic. I read all about sealing air gaps and venting and I need something around R-30 to R-49 by the charts for south florida.

Question 1: Am I correct, to get to around an R-40 rating I will need at least 12" deep blown insulation.

The one thing I haven't found is a discussion of safety issues.

Question 2: In an old house like this, do I have any safety concerns covering up old wiring, light fixtures,junction boxes, etc, with 12" of blown cellulose. thanks
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Old 09-09-2015, 10:18 AM   #2
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Some guys don't like cellulose in hot and humid climates.

There are a couple of good threads on here about Florida insulation questions. I would definitely look at incorporating a radiant barrier into your insulation retrofits.
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Old 09-09-2015, 10:24 AM   #3
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Since the electrical could be an issue, inspect it before you insulate. Or have it inspected by an electrician.
All connections should be in covered junction boxes.
All wires properly secured to framing members.
Check sheathings to make sure all are intact and not eaten by rodents.
Electrical wiring covered by insulation, in good condition, shouldn't be a concern.
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Old 09-09-2015, 06:15 PM   #4
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the whole project is not quit as simple as I first thought; at least not if I do it correctly, but I guess doing anything will be better that doing nothing.

I have been unable to find anything about not using cellulose in Florida.
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Old 09-14-2015, 06:30 PM   #5
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maybe Windows can leave a few links for you...

cellulose in Fl.; http://www.floridaenergy.ufl.edu/wp-...tion_final.pdf

calculating; http://www.greenfiber.com/step_one_-...o_install.html

Check with local AHJ; http://energycode.pnl.gov/EnergyCode...?state=Florida

Safety tips; http://www.greenbuildingadvisor.com/...ose-insulation

http://www.nationalfiber.com/docs/Te...Lights0410.pdf

be sure to air seal first and wrap the AC ducting that will be exposed after the application.

Gary
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17,000 dryer fires a year, when did you last clean the inside of the dryer near motor or the exhaust ducting?
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Old 09-14-2015, 08:35 PM   #6
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thanks for the links. A couple were very helpful, but nothing in any of them about not using cellulose in Florida
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Old 09-15-2015, 06:08 AM   #7
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None of the links that Gary provided mention anything about cellulose in Florida.

There is an awful lot of claims about cellulose in hot humid climates (i.e. concerns about fire retardants washing out) but little science.

Here is a blog that references just that: http://blog.srmi.biz/energy-saving-t...-vs-cellulose/

And then a more technical document that refutes that: https://greenspec.buildinggreen.com/...-pros-and-cons

This tidbit on fire retardants washing out was funny: As for evaporation (sublimation) of boric acid from cellulose, the study found that at very high temperatures (90C or 194F) and 100% relative humidity, the loss of boric acid was significant, but the loss was negligible when the temperature is lower 70C (158F), even at 100% humidity and air exchange rates of 2.0 attic changes per hour. “It appears that it would take 300 years or more at 70C, 100% relative humidity, and air exchange rates from 1.0 to 2.0 attic volumes per hour to lose enough boric acid to significantly affect the combustion tests
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Old 09-15-2015, 08:08 AM   #8
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Thank you very much; much what I suspected. Fiberglass was really something I didn't want to use for a number of reasons.
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Old 09-20-2015, 09:47 PM   #9
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I agree. That first link of mine did mention cellulose comparing R-values, and it was written from Fl... I have a few links on radiant with cellulose, the improvements sited, if interested. Be sure to box-out any light boxes/cans (not rated "IC") and don't cover knob&tube with it; http://michaelbluejay.com/electricity/insulation.html

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Old 09-21-2015, 06:44 AM   #10
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Also proper amount of roof venting is very important.
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Old 09-21-2015, 09:46 AM   #11
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Quote:
Originally Posted by joecaption
Also proper amount of roof venting is very important.
Getting in before Gary corrects you.
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Old 09-23-2015, 11:04 PM   #12
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I've corrected Joe three times, I believe, in as many years. You, another story... lol. At least I don't have a business where prospective customers can go on the internet for a better incite as to who they might be dealing with... thanks for the ridiculing zinger.

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Old 09-24-2015, 12:28 AM   #13
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Quote:
Originally Posted by Gary in WA View Post
I've corrected Joe three times, I believe, in as many years. You, another story... lol. At least I don't have a business where prospective customers can go on the internet for a better incite as to who they might be dealing with... thanks for the ridiculing zinger.

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I think you meant "insight" Gary...right?

Thanks for the compliment. I hope that I can bring a little humor to the forum from time to time. Its really easy for folks to get bent out of shape. If we take ourselves too seriously, it's really easy to get overly sensitive about silly stuff.
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