Topping up Attic Insulation: Blown Fiberglass or Cellulose?

Cellulose will preform better in attic. It will settle so blow more than what you desire for depth. we blow both but im in Syracuse I dont know anyone out there. I have found if you go up and feel in the insulation you will feel the heat in the blown fiberglass much higher than the cellulose almost near sheetrock. Also when it dips under 10 degrees the r-value of fiberglass drops significantly more than cellulose does. Walls are a totally different subject though.

I had blown in fiberglass placed above the old R-9 batts in my attic about a year and a half ago. The nicer blown in FG doesn't itch and is much less dusty than I remember the cellulose being. It's white too. I chose FG because cellulose is food for lots of animals, food for fire, and seems like somebody's grand idea to recycle more than an innovation. It is also heavier and settles more than FG. My old sheetrock doesn't need more weight on it. FG and cellulose are the same R value per inch so no benefit there.

I couldn't see any reason to use cellulose but plenty reasons not to.

I spent lots of time before the blow in going around and sealing all penetrations and installing baffles along the eaves to prevent blocking the ventilation. The old FG batts are super itchy. Your old FG batts include the Vapor barrier so the only benefit I've heard of for cellulose, better air sealing, doesn't matter.

Be sure to take the time and seal the air gaps around likght boxes, wire penetrations, plumbing penetrations etc. Also, after the blowing, go up there and be sure that they didn't fill your insulation guard around the chimney with insulation. Even though it won't burn like cellullose, you want that clearance to combustibles.

A local fire in a house started from blow in cellulose insulation. But it was also next to the flue.

http://www.ksl.com/index.php?nid=148&sid=8683892


Fire raises concerns over home insulation
November 15th, 2009 @ 9:45pm
By Nicole Gonzales

LAYTON -- A house fire in Layton displaced a family and caused thousands of dollars in damage Saturday.

Fire investigators said it started near the chimney flue in the attic. They said the insulation was too close to the hot pipe and caught fire -- a problem that could become more common as the winter sets in.

The house, located near 1500 North and Cherry Lane, was declared unlivable. The cost of the damage to the home was estimated at $85,000.

"The past two days we've had two fires -- chimney fire-related -- so this is a concern to us right now," said Doug Bitton with the Layton City Fire Department.

The concern was the fire's origin.

"This vent pipe has a lot of white impingement marks right here," Bitton said.

Bitton investigated for Layton City Fire and said the white marks show where the insulation ignited.

The homeowner had cellulose insulation blown in this spring, thinking it would save energy and money. Just the opposite happened, however.

The family lit their wood burning stove around 4 p.m. Saturday. By 8:00, they knew something was wrong.

"First the electrical went off in the family room, which surprised them, and then they saw a different haze -- color of light -- out the rear of their home," said Bitton.

They evacuated just in time for crews to start their work on the attic. The fire spread through the insulation, so they had to remove most of it.

An hour later the fire was out, and the family was forced out as well.

Bitton said all families need to check the clearance between their flues and the insulation. Most building codes recommend 1 to 2 inches of space, depending on the pipe.

The U.S. Department of Energy suggests putting in a clearance dam or a protective sleeve.

"We don't want any radiant heat hitting this type of cellulose insulation that could cause a possible combustion," said Bitton.

Bitton said local code officials can help people make the right adjustments.

Food for thought...

Cellulose has been given a bad rap and had improved greatly through the years: it's treated w/ borates that make it very fire retardant as well as a deterrent the mice, vermin and mold. Any insulating material if installed improperly can cause fire (ie around old light fixtures etc). If the chimney runs through the attic then you need to build up a dam of fiberglass batts around it.

One problem that loose FG has that cellulose doesn't is air washing that can dramatically reduce r-value: As the temperature difference between the living space and attic increases, the R-value of blown fiberglass diminishes. In extreme situations, such as the upper Midwest, this reduction in R-value approaches 50 percent.
This phenomena seems to occur as a result of thermal convection. The trapped air molecules in the insulation are pulled up through the insulation into the colder attic air. This problem is apparently solved by installing fiberglass batt insulation over the top of loose fill or blown insulation.

Highbeam said:

Also, after the blowing, go up there and be sure that they didn't fill your insulation guard around the chimney with insulation. Even though it won't burn like cellullose, you want that clearance to combustibles.

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HB,

Could you explain what you mean by "insulation guard"?

Shari

I know for my double wall stainless chimney, the chimney guard is just a piece of metal that goes over the outside of the pipe making a 2" air gap between the pipe and the insulation and you can then pack your insulation around the guard safely. A few months ago, I was unbiased and read and read the benefits of both cellulose and fiberglass and went with cellulose as the hands down winner. I read contractor forums, safety information, reviews and specs for both because it''s a big investment and I wanted to use the best product. Just do a lot of research and pick what you think is right for you. I love the youtube video of the guy "proving' that cellulose burns by taking a blowtorch to it for several seconds.

I've got cellulose in the entire house (interior and exterior walls and attic). The guys that did the walls did a great job, however the guy that came back to do my attic was apparently trying to save some time and insulation. I didn't bother to check behind all the ductwork closely until several months afterwards. So, a month or so ago I rented the equipment from Lowes and put an additional 17 bags in the attic (and 3 in my garage, but still need more there). I never even considered fiberglass of any kind. I use my attic for storage, and the air handler is up there. So, didn't want FG blowing around, and getting me all itchy... I have taken a torch to the cellulose just to see, it will burn, but goes out as soon as you pull the torch away. It is flame retardant, not proof. I bet a torch on blown FG would do something similar... I've had no trouble with pests in the attic, and can't say that I've really even seen any insects (now I'll probably be flooded with bugs, and rodents since I said this)...

Just my $.02, but I prefer cellulose... very easy to do yourself too... I'll be finishing the ceiling and walls of my garage with it sometime this winter or next spring... It works GREAT for sound insulation...

Shari said:

Highbeam said:

Also, after the blowing, go up there and be sure that they didn't fill your insulation guard around the chimney with insulation. Even though it won't burn like cellullose, you want that clearance to combustibles.

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HB,

Could you explain what you mean by "insulation guard"?

Shari

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It is the metal shield around your chimney that provides the 2" required clearance to combustibles which can be the wood framing or the insulation. The "ceiling support box" on my simpson system extends into the room about 2 inches but runs into the attic about two feet. The support box is the insulation shield.

Back to chemistry class guys. Things that end in "ose" are sugars. Things about sucrose, lactose, fructose, and ..... cellulose. Hmmm, do you really want to fill your attic with cotton candy? What happens when you pour a pepsi out on the concrete in the summer? Ants eat it, bees eat it, all kinds of bugs that I don't want in my attic. Have you ever started a sugar cube on fire? Just light it. And yes, that sugar feeds all sorts of microorganisms too for mold and who knows what else. What happens when cotton candy gets wet? Just imagine the syrup pouring through your sheetrock.

I don't trust for a minute, much less bet my life on it, that the proper amounts of some additive were sprinkled into the cotton candy to make it less tasty to bugs, fire, or mold. That is like them saying that they added lubricity back into the new diesel (per fed regulations) to make it equal to the old diesel when we all know that they didn't and now we have to add lubricity additives.

So I know that the above cellulose trash talk may be on the extreme end but there are no negatives to the FG which is an inert product and not a sugar.

Highbeam said:

Back to chemistry class guys. Things that end in "ose" are sugars. Things about sucrose, lactose, fructose, and ..... cellulose. Hmmm, do you really want to fill your attic with cotton candy? What happens when you pour a pepsi out on the concrete in the summer? Ants eat it, bees eat it, all kinds of bugs that I don't want in my attic. Have you ever started a sugar cube on fire? Just light it. And yes, that sugar feeds all sorts of microorganisms too for mold and who knows what else. What happens when cotton candy gets wet? Just imagine the syrup pouring through your sheetrock.

I don't trust for a minute, much less bet my life on it, that the proper amounts of some additive were sprinkled into the cotton candy to make it less tasty to bugs, fire, or mold. That is like them saying that they added lubricity back into the new diesel (per fed regulations) to make it equal to the old diesel when we all know that they didn't and now we have to add lubricity additives.

So I know that the above cellulose trash talk may be on the extreme end but there are no negatives to the FG which is an inert product and not a sugar.

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Better watch out, your house is framed with peppermint sticks.

You think you got it bad - my knitting needles are made with cheese.
http://www.fibersden.com/casein-knitting-needles/

I know, LOL, but there is no easy alternative there and the wood isn't prechewed. You can bet I would love to have a house built with ICFs and steel trusses. There are some really cool ideas out there and in other countries that aren't obsessed with wood construction.

I just got another quote over the phone. 1000 ft2, $835 for fiberglass and $900 for cellulose.
I think we have a winner.

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Which are you doing? House of glass or gingerbread?

Oddly enough, last night on the local news there was a piece about a house that burnt down in my home town yesterday.
They didn't say the cause of the fire but they interviewed a fireman who made some vague comments about it being filled with cellulose, and having to "dig through it" for a long time". He didn't really say exactly what he meant - but I got the impression that it was a smoldering issue - which of course could re-ignite, I suppose.

Back during the first energy crunch there was lots of federal money to insulate public buildings (sound familiar?). There was not a lot of money to fix roof leaks or install vapor barriers. The net result was more than a few buildings with collapsed interior ceilings when the blown in cellulose absorbed moisture from leaks or humidity. Granted fiberglass can absorb some water but nothing like Cellulose.

I've always heard you should alternate types of insulation. If you have batts then go with blown in then go with batts again if you add more and vice versa. Just my .01 worth

I don't know about that. I think you can blow in on top of blown in all day long. Trying to lay batts over blown-in would be difficult to do well. There will always be dips and rises with the blown-in and your batts are supposed to lay against something with no air gaps. The batts are no fun at all in the attic, ever. Blown in is just so easy and such a better product that I would rather blow in cellulose than lay FG batts.

velvetfoot said:

I think it's hard to find impartial information on insulation.

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I found the same thing. I used blown in FG so I might be biased towards that since it's been great. At the end of the day, lots of people use both cellulose and fiberglass and most don't even know which they have. Since you asked for our opinions though....

Rolling out batts, that totally sucks. There's nothing fun about it and even if you hire it out you can be sure that they didn't lay it down as consistently as if it was blown in. They will leave gaps and cracks, or you will leave gaps and cracks. You just can't do it perfectly.

Fiberglass is safer in the case of a fire yes, but if your house is on fire and its in the attic is there anything to save? lets focus on not letting a fire happen. Cellulose preforms better in the attic than fiberglass.... talk to any energy star or building performance institute (bpi) inspector. I have also seen what cellulose turns into when its twenty years old....powder. I do both applications personally. In my house i have an R60 bottom half blown fiberglass top half cellulose. The main thing is get airsealing done its more important than adding more insulation. Look for contractor that usually does new construction they will have a better price than an insulator that does retrofit work. They shouldnt be that busy not a lot of building happening. my company would blow r30 for $ .60sqft depending on your attic size, room, baffle installed or not. Good luck

I suppose it would be rather pointless to warn members of this forum not to play with fire...

NEDLAX said:

Fiberglass is safer in the case of a fire yes, but if your house is on fire and its in the attic is there anything to save? lets focus on not letting a fire happen. Cellulose preforms better in the attic than fiberglass.... talk to any energy star or building performance institute (bpi) inspector. I have also seen what cellulose turns into when its twenty years old....powder. I do both applications personally. In my house i have an R60 bottom half blown fiberglass top half cellulose. The main thing is get airsealing done its more important than adding more insulation. Look for contractor that usually does new construction they will have a better price than an insulator that does retrofit work. They shouldnt be that busy not a lot of building happening. my company would blow r30 for $ .60sqft depending on your attic size, room, baffle installed or not. Good luck

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Since you're in the business...do you know what ever happened to rock wool?
My old house was at some point in the distant past blown full of it but I never hear of it now.