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Old 05-15-2011, 02:03 PM
 
Location: Austin, TX
16,787 posts, read 48,846,479 times
Reputation: 9477

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Make sure the insulation that is added does not block the air flow from your soffit vents.

Most attics need better ventilation as they rarely meet the current ventilation recommendations. But I recommend venting them with passive ventilation, not with fans. Roof fans typically use more energy then they save in heating costs. I recently doubled the number of soffit vents I have on my house and plan on adding additional ridge vents.

The current code recommendations for ventilation attic space are:

Intake soffit vents:
-continuous vents: 1 sf vent to 300 sf insulated attic space
-non continuous: 1 sf vent to 150 sf insulated attic ceiling area

Exhaust vents at or near the peak of the roof: Exhaust area should be at least half of the intake area.

Continuous ridge and hip vents are recommended for the exhaust. Mushroom type vents will do if you can get enough area with them, which can be difficult with some roof shapes.
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Old 05-15-2011, 04:35 PM
 
Location: A little suburb of Houston
3,702 posts, read 18,155,517 times
Reputation: 2090
Quote:
Originally Posted by CptnRn View Post
Make sure the insulation that is added does not block the air flow from your soffit vents.

Most attics need better ventilation as they rarely meet the current ventilation recommendations. But I recommend venting them with passive ventilation, not with fans. Roof fans typically use more energy then they save in heating costs. I recently doubled the number of soffit vents I have on my house and plan on adding additional ridge vents.

The current code recommendations for ventilation attic space are:

Intake soffit vents:
-continuous vents: 1 sf vent to 300 sf insulated attic space
-non continuous: 1 sf vent to 150 sf insulated attic ceiling area

Exhaust vents at or near the peak of the roof: Exhaust area should be at least half of the intake area.

Continuous ridge and hip vents are recommended for the exhaust. Mushroom type vents will do if you can get enough area with them, which can be difficult with some roof shapes.
I second that. My house had gable vents. We blocked those and added soffit and ridge vents...made a huge difference.
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Old 05-15-2011, 05:43 PM
 
Location: Austin, TX
16,787 posts, read 48,846,479 times
Reputation: 9477
Quote:
Originally Posted by Canine*Castle View Post
smtimelevi ... Thanks for your post. It seems many prefer the fiberglass. Hopefully, with the years I have left on Earth, the cellulose will "do me well."
P.S. I'm thinking about installing a few roof fans too. We'll see.

CaptRn ... Measured the joists ... 24 inches apart ... Thanks for the advice.
This thread should probably be moved to the housing thread.

Quote:
Originally Posted by Canine*Castle
My thought on the increase to nearly R49 was to add a total of R38 cellulose and the rock wool (5 inches - R10) that's already there would bring the insulation to an R48. Right now, the contractor is just quoting R30 to bring it up to R40 with the r/w. Anyway, this is regarding an electric company rebate although they're wanted the insulation to be 17". Of course, the difference in fiberglass and cellulose in inches is great. In their clause, they left out the most important thing, the R factor. Duh! They told me that if the contractor can write about something and something equaling whatever, it would probably qualify for the rebate. Of course, now I'm worried about the weight because if it doesn't, then bringing it to 17" won't be good. My contractor guy never mentioned anything about the weight. ...

Anyway, what do you think about the weight of R38 and the R10 r/w or should I just stick with the R30 cellulose? As I said on the forum, my joists are 24" apart. I don't know the thickness of the drywall or whatever it's called. So if I were to go with fiberglass, then the 17" wouldn't be a problem, but I just don't think I will like that stuff because it's too airy even though I'm told it doesn't settle like cellulose.

Well, thanks for listening, for your time, and giving me any advice that you'd like too. I'm going to be so ticked if I don't get my rebate.
You are welcome. I hope this helps rather then add to your confusion.

Residential drywall is almost always 1/2".

Rockwool is heavier then Cellulose so, since you already have 5" of rockwool, adding enough additional rockwool or cellulose to get to R-38 is not recommended with a 24" joist spacing.

So in your case you should go with the fiberglass insulation.

If you have an R-10 with the existing rockwool insulation, then you need to add:

10.37" to 12.72"* of fiberglass to get to an R-38;

and

14.4" to 17.71"* of fiberglass to get to an R-49

* the variation depends whether the fiberglass is rated at a R value of 2.2 or 2.7/inch.

If your electric company is asking for a TOTAL of 17" of insulation, it sounds like they are shooting for an R-38 rating.

If they are asking you to ADD 17" of insulation it sounds like they are shooting for an R-49 rating.

I'd call the electric company and make sure you understand what it is they are asking for, just to make sure. You definitely should try to get any rebate you can.

Last edited by CptnRn; 05-15-2011 at 06:27 PM.. Reason: Edit: 24" not 16" joist spacing..
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Old 05-15-2011, 06:26 PM
 
Location: Somewhere in Texas
5,406 posts, read 13,227,516 times
Reputation: 2800
Yes, I thought about posting it there, but I thought since I live in Texas, there would be people in this area who would have comments. I actually did a search in the housing section, but found very little information about attic insulation.

I've printed out the information you've given me, CaptRN and will ask the contractor more questions. That's all I need is to have my ceilings sag. Ugh.
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Old 05-15-2011, 08:59 PM
 
Location: Somewhere in Texas
5,406 posts, read 13,227,516 times
Reputation: 2800
Okay, CaptRn. Here I thought I was sold on cellulose but after you sent the link about the weight, the plan has changed. I just got off the phone with the installation guy and he said usually when ceiling joists were 24" apart, the drywall was 3/4" which would hold the R38. Well, we don't know for sure if it is and I said I didn't want any holes cut in my ceiling to find out, so fiber glass it will be. I'd rather be safe than sorry. He said he's never heard of ceilings sagging, but that doesn't mean it can't happen. I'm so glad to learn he uses the white fiberglass (Johns Manville) and not the pink. It is not itchy like the pink. All in all, I would still prefer the cellulose but your point about the weight is priceless. Thanks again for all your help.

Thanks to you fiberglass lovers too confirming that it, as well, is a good product.
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Old 05-15-2011, 11:49 PM
 
Location: So California
8,704 posts, read 11,051,411 times
Reputation: 4794
For older houses, adding traditional insulation is not a bad way to go for an inexpensive fix. For new construction or more significant renovation, full encapulation spray foam is far superior. Full encapsulation is the concept of encapsulating the home walls and roof into one building envelope. Getting rid of the hot and inefficient attic and greatly reducing outside air infiltration. Ive been doing this process on new construction for several years and have yielded energy savings well over 50%.
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Old 05-16-2011, 09:02 PM
 
89 posts, read 185,168 times
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Quote:
Originally Posted by slo1318 View Post
For older houses, adding traditional insulation is not a bad way to go for an inexpensive fix. For new construction or more significant renovation, full encapulation spray foam is far superior. Full encapsulation is the concept of encapsulating the home walls and roof into one building envelope. Getting rid of the hot and inefficient attic and greatly reducing outside air infiltration. Ive been doing this process on new construction for several years and have yielded energy savings well over 50%.
The draw back with that stuff is that it can be highly flammable.
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Old 05-16-2011, 09:54 PM
 
95 posts, read 205,364 times
Reputation: 80
Cellulose is a good product when retrofitting wall insulation in an existing home but I would strongly recommend not doing it in the attic. A lot of people choose it because its a green friendly product and is recycled paper. It is a good insulator but it has several cons when speaking of attic installations.

- It has a higher r-value per square inch which is great but its heavy and will put weight on the sheetrock
- Contrary to what is advertised it does and will retain moisture. It's paper.
- Advertised as pest resistant because Boric Acid is added to it and is a toxic pesticide. However, it does not repel large rodents which is what people would naturally assume with that statement and rodents love it. Its like installing a litter box in your attic.
- As mentioned it has Boric Acid which is added for fire resistance. When cellulose gets wet it releases the Boric Acid which will corrode wiring and piping. As long as it doesn't get wet, which it often does in the hill country where I reside, then it will not corrode wiring and piping per the advertisement.
- The recommended installation calls for it to be blown in damp... This is because it is incredibly dusty. Ever picked up a newspaper and had black stuff all on your hands? Welcome to your new attic.
- It will get in your duct work because chances are you didn't have them sealed before the install and like I mentioned it is incredibly dusty and easily sucked in, or leaked out thru cracks, or moved around in the attic if you need to do work.
- It WILL degrade over time. It is heavy and it will settle up to a couple inches.
- It's cheap. That's why your installer wants you to buy it. The markup is huge.


If you are going to have Cellulose installed walls or attic ask for Bora-Free. Applegate is one company that makes a product called Bora-Spray which is free of Boric Acid.


Fiberglass is a better choice for the attic but it does have it's cons. It isn't recycled and does have a lower fire tolerance per some tests but not so much so to be a real deciding factor. It will not degrade over time because its lighter, it will not retain moisture because its glass, and it will not ever corrode anything.

However, it will itch if you get it on you and it can have high amounts of formaldehyde which can cause your house to stink like cat pee for months. There is good news though. White insulation has very low amounts of formaldehyde, it is less itchy, and it has low VOC's (Volatile Organic Compounds). Most pink and yellow insulation has high traces of both VOC and Formaldehyde due being added in order to make batt insulation. Pink and yellow blown in is nothing more then the left over cut pieces of batt insulation being ground up to make blown in with the exception of Owens Corning whom adds it for marketing purposes.

Lastly, any choice that you make you need to look for one thing. Is it GREENGUARD Certified? If it is then it has been tested to give you a higher indoor air quality and a low amount of VOC's.

Hopefully this information is helpful for others as it sounds like you have already made a good decision about insulation. That said before you do ANYTHING have all of your ducts sealed. As well do not just stop with insulation. As mentioned ventilation is a huge culprit to high energy bills. In addition I would look into a SPRAY ON radiant barrier over a foil but that's a whole different paragraph to write.

Look at my name. It's safe to say I know a little about this... I work for the largest energy efficiency company in the nation that specializes exclusively in existing residential upgrades predominantly in the attic space. Moderator cut: see comment

Last edited by Bo; 05-17-2011 at 10:28 AM.. Reason: The ad rules of the board state that you can mention your business in your member profile, but not in a post.
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