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Old 08-25-2014, 03:40 PM   #1
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Spray Foam or Cellulose in Attic


I need some help deciding what type of insulation to use in my attic. I purchased a house knowing that it has very little attic insulation and would need some work. It is a cape cod style home, with a walk up attic. Ideally we would like to use the attic area for storage, as it is fairly large. It currently has some fiber glass bats loosely rolled out on the floor; that is it. No air sealing, nothing in the roof joists.

I have been told I have two options. Option 1 is to blow in cellulose on top of the fiber glass. This is probably the cheapest option. One downfall is that it will virtually eliminate all potential storage space.
Option 2 is to spray foam the roof joists, completely air sealing the house envelope, and effectively making the attic a pseudo living space. Downfall of this option is that it will probably be pretty expensive. And to fully utilize the space, I would need to remove all the old fiberglass.

I am torn on what to do, as I have read proponents of both approaches. The decision will probably come down to cost, but I am hoping someone out there may have some insight into things I may not have considered. Any insight or help would be welcomed.
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Old 08-25-2014, 03:51 PM   #2
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Spray Foam or Cellulose in Attic


Foam is worth the cost.

Fills all the air-gaps, is easily shaped after the setup to be covered by sheet goods, saves money on heating and cooling. Will not have dust filtering down from the attic into your living space.

Cellulose will have dust falling into your living space forever.

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Old 08-25-2014, 05:30 PM   #3
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Spray Foam or Cellulose in Attic


I think you have noodled it pretty well out.

Cost vs. Usage.

I am not as big a fan of foam as de-nagorg but for the purposes of making a roof plane insulated, there isn't much more effective.

Be sure to figure in the intumescent paint as part of the equation as well as it will be code mandated.
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Old 08-25-2014, 06:17 PM   #4
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Spray Foam or Cellulose in Attic


We went with blown in insulation for our cape cod. We have a nice walk in door to the attic and will lose some attic storage so I built a raised platform for storage. Still working on it as it is just too hot these days in there. If you go that route, air seal as much as you can before.

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Old 08-26-2014, 06:24 AM   #5
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Spray Foam or Cellulose in Attic


Well said HDS and it is worth noting, as you pointed out, you can insulate a cape effectively without having to spray foam the roof deck.
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Old 08-26-2014, 07:48 AM   #6
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Spray Foam or Cellulose in Attic


Thank you all for the help. I have a couple of follow up questions.


If I were to decide to go with the blown in cellulose, air sealing seems to be a very important first step. To air seal properly, would I want to more-or-less remove all the existing fiberglass? In order to properly identify and seal all potential air leaks?


What is " intumescent paint"? I am assuming this is a paint that must cover the foam as a fire wall of some sort?


Thanks for the replies so far. Exactly the info I was hoping for.
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Old 08-26-2014, 08:35 AM   #7
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Spray Foam or Cellulose in Attic


You don't need to "remove" it per se but you do need to move it around.

Intumescent paint is require for ignition barrier compliance when you have exposed foams.

Make check payable to....
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Old 08-26-2014, 10:19 AM   #8
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Spray Foam or Cellulose in Attic


As WoW mentioned, you'll want to move it around to get access to the areas that may need addressing.

It would have cost us a lot to spray foam the roof deck. The cost of the foam was one issue. The second was our roof rafters are only 2x6's and we would have either had to replace the roof so as to add rigid foam on the top of the roof deck as well to get to an R40. The spray foam would have only given us an R20ish, plus we would have needed to add at least 4" of rigid foam to the roof deck. That gets mighty costly. Especially since we had just spent about $5000 for the gutters, soffits, eves and rakes to be replaced/reclad. Could have reused the gutters, but the soffits, rakes and eves would all be wasted since the roof would be raised.

At the time those were done, the roof was in pretty good shape, unfortunately it does now need to be replaced. If we had know that then, might have gone a different route.

So depending on your rafter depth, you may not be able to get the full R value needed and may need to add rigid foam to the roof deck (hence a new roof and such).

It is a nice idea, but unless you have major HVAC duct work in your attic, not sure it is always the best approach due to a cost stand point.
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Old 08-26-2014, 10:28 AM   #9
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Spray Foam or Cellulose in Attic


If you go with the blown in, besides the air sealing, make sure you insulate and seal up the knee walls. If you just have batts of insulation in the knee walls, adding Tyvek will help air seal the insulation. You lose about 40% of the insulating value due to air movement through the fiberglass insulation. Also the floor joists between the attic and the living space should be blocked off. Much easier to do without all the added blown in insulation. In fact, I have to go back and fix about 10 of those as I ran out of time before the insulation was installed.

For the rest of the air sealing, look for electrical runs, light fixtures in the ceiling below. duct work, etc... I used a combination of Great Stuff and fire rated caulk/sealant.

Good luck and let us know how it goes.
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Old 08-26-2014, 11:36 AM   #10
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Spray Foam or Cellulose in Attic


I laugh a lot at the seal off stuff. one of the building inspectors I know pointed out that 95% of the building is sealed off by the sheetrock and mud and tapping. the number one area of air infultrations is 1. windows and doors. 2 penetrations for plumbing and electrical. and the bottom plate of extirior walls. Also he brought up Foam insulation. It is prohibited in being used in the uderside of the roof in the jurisdiction were I live. because if the roof gets damaged shingles get lose and you have a leak. you are going to have more damage then you want to think about. Just think if you had to replace some of the sheathing a few years after you foamed that underside of the roof! Have fun with that. Plus Foam is toxic! The EPA and the CDC are investigating people who have had foam insulation placed in their home that have come down with asthma and other health issues and how long the off gassing lasts. some reseach has shown that even though we can not smell it it still off gasses well over two years of VOC's. thinka about it it is two petroleum products mixed to form a chemical reaction. two insulations virgin fiberglass blown in or shreded news paper. either one will do what you want.
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Old 08-26-2014, 01:15 PM   #11
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Spray Foam or Cellulose in Attic


Well I thought I was highly leaning towards removing the old, dirty fiberglass, and adding spray foam to the ceiling/roof. But after reading some of these posts I am back on the fence.




I really like the ide of having the extra space in the attic for storage, and I don't see how to achieve that without using the spray foam.


But, the spray foam is:
  • Highly flammable?
  • Toxic / High VOC's?
  • Super Expensive
  • Prone to causing substantial water damage should there be any type of leak in the roof?
Has anyone out there gone the spray foam route and ultimately been happy with their decision? Some of these warnings make spray foam sound like I am setting my family up for doomsday!
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Old 08-26-2014, 06:29 PM   #12
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Spray Foam or Cellulose in Attic


I don't think spray foams are dangerous if installed properly. But they do require a thermal or ignition barrier depending on your local code and where they are used.

As for pricing, only way to know is to get some quotes.

As for leaking, I saw a video where it protected the inside after water from a fire hose ripped the shingles off. Granted this was a spray foam company's video.

Do you not have room to build a raised platform in the attic to accommodate the added insulation?
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Old 08-27-2014, 07:19 AM   #13
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Yes, air sealing is vital to creating a sealed attic space. Forget the "great stuff" cans. The actual professional stuff comes in two tanks that look like propane tanks for your grill, and they mix in the nozzle that you use to spray the foam. It was $700 for the small tanks and they were plenty for completely air sealing a 1400 sq ft attic. You want to do that while it is HOT out, you get maximum foam expansion when it's hot, the colder it is the more compact the foam stays and that's not idea.

It wasn't difficult to do, but it stinks to high heaven. You'll need one of the canister respirators to protect your lungs. Every quote I got to have someone else do it started at $2,000 and went up from there. It made much more sense to do it myself.

You'll want to move all of the fiberglass out of the way, then seal the tops of all of your stud bays, rim joists, all electric runs, all ceiling fixtures, etc. Basically any place that air can get through you cover with foam. Every wall, interior and exterior, in our home opened up into the attic so we effectively had "chimneys" of warm air channeled up into the space. Not great for the utility bills!

Personally, I don't see a point in putting the cellulose over the fiberglass, as the fiberglass will just compress and be useless anyway. But that's your call.

I'm not sure how cellulose would "will have dust falling into your living space forever" because if everything is air sealed properly how would it get through? We've had it for three years now, and no additional dust has shown up in the house.
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Old 08-27-2014, 08:11 AM   #14
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Spray Foam or Cellulose in Attic


Quote:
Originally Posted by mnp13
Yes, air sealing is vital to creating a sealed attic space. Forget the "great stuff" cans. The actual professional stuff comes in two tanks that look like propane tanks for your grill, and they mix in the nozzle that you use to spray the foam. It was $700 for the small tanks and they were plenty for completely air sealing a 1400 sq ft attic. You want to do that while it is HOT out, you get maximum foam expansion when it's hot, the colder it is the more compact the foam stays and that's not idea. It wasn't difficult to do, but it stinks to high heaven. You'll need one of the canister respirators to protect your lungs. Every quote I got to have someone else do it started at $2,000 and went up from there. It made much more sense to do it myself. You'll want to move all of the fiberglass out of the way, then seal the tops of all of your stud bays, rim joists, all electric runs, all ceiling fixtures, etc. Basically any place that air can get through you cover with foam. Every wall, interior and exterior, in our home opened up into the attic so we effectively had "chimneys" of warm air channeled up into the space. Not great for the utility bills! Personally, I don't see a point in putting the cellulose over the fiberglass, as the fiberglass will just compress and be useless anyway. But that's your call. I'm not sure how cellulose would "will have dust falling into your living space forever" because if everything is air sealed properly how would it get through? We've had it for three years now, and no additional dust has shown up in the house.
About 95% correct.

The tanks do you have better yield when it's warm but you don't necessarily need to work in a hot attic per se. You can warm the tanks downstairs and they will keep a good amount of the heat inside of them even if you're working up in the attic in the cooler fall temperatures.

The fiberglass insulation is by no means worthless. Even compressed fiberglass has a measured amount of R-value although slightly less than that of properly installed height.

There is no point in throwing it out and less is contaminated with animal feces or some other sort of biological.

Props to you for doing it on your own. It is one of the more messy jobs for a DIYer and most people won't want the hassle.
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Old 08-27-2014, 02:36 PM   #15
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Spray Foam or Cellulose in Attic


Quote:
The tanks do you have better yield when it's warm but you don't necessarily need to work in a hot attic per se. You can warm the tanks downstairs and they will keep a good amount of the heat inside of them even if you're working up in the attic in the cooler fall temperatures.
I did the foam in February when the attic was around freezing. We put the tanks in the small bathroom overnight with two heaters running to get them up over 85 degrees, then wrapped them in thermal blankets inside big Rubbermaid bins to keep them warm while I worked. My husband's job was to shove the tanks along behind me so that I could work as quickly as possible. It was a BIG pain in the neck.

So, yes, it's definitely possible to do the work at other times of the year, but it would have been MUCH easier if it had been done when the attic was hot already. Or even in the fall or spring when it was in the 50's or 60's instead of the 30's when I did it.

The tanks were warm, therefore the foam was warm, but it was in a very cold attic so I think we still lost some expansion. The more expansion, the better your R- value so the farther your investment goes.

Thanks for the correction on the fiberglass, actually I think it was someone here who told me not to bother with it. Most of ours was very dirty and full of raccoon crap, squirrel nests and ticks so the majority was going anyway.

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