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Insulating an Attic - Spray Foam in the Rafters v. Cellulose on the Floor

Insulating an Attic - Spray Foam in the Rafters v. Cellulose on the Floor


  #1  
Old 03-29-14, 08:59 AM
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Insulating an Attic - Spray Foam in the Rafters v. Cellulose on the Floor

My house is a single story ranch in Connecticut and it was built in 1957. The attic has about 4-5 inches of fiberglass insulation in the floor of the attic, but it is matted down after all these years. I believe I’m a losing a lot of heat through the attic so I want to fix this issue.

I have looked into blowing in cellulose insulation over the existing fiberglass insulation, but after speaking with a contractor there are a number of steps that need to happen first. The contractor told me that first they would have to seal (with some type of spray foam) all penetrations between the attic floor and the living space below. This includes any electrical wiring, plumbing pipes (vent stacks), and the chimney. They’d also install an insulated door over the pull down latter. Furthermore, there is an air handler for the air conditioning on the attic floor and there is also plywood down the center of the attic to allow a walking space in the attic to service the air handler and general storage. The cellulose cannot cover these areas the contractor told me they’d build barriers out of plywood around these areas keeping the cellulose out of these areas and also add a layer of rigid foam and another layer of plywood to add some additional insulation to these areas.

The contractor also offered another alternative, which he seemed to prefer and I think I prefer it too. He told me they could insulate the attic ceiling and the gable walls with open cell spray foam, which also needs to be coated with a fired retardant, which is also sprayed on like paint. He also indicated that when they fill the roof rafter bays and the gable wall stud bays that they would actually over fill these areas and cover the rafters and studs to add a greater thermal barrier. This all seems to be a good solution and the contractor suggested that this will make the attic cooler in the summer and warmer in the winter even though it is still not conditioned space. He also suggested the A/C air handler would not have to work as hard and may last longer.

We then discussed my exiting ridge vent, soffit vents, and roof fan. He told be the ridge vent would still exist, but it would not have a function and would be covered on the inside with the spray foam. The roof fan can be spray foamed over or I could remove it and patch the roof before they apply the spray foam. He also told me that the rafter bays would be completely filled with the spray foam so there would no longer be a need for air circulation in the rafters and no need for the ridge vent. The soffits would still have air circulation as they would install a barrier so the spray foam does NOT fill up the soffits.
Both alternatives are about the same price and I am leaning toward the spray foam.

One question I have is with the spray foam alternative do I need to remove the existing fiberglass insulation in the attic floor? The contractor said it can stay, but if I want they would also remove it for $1.00 per square foot by stuffing it into plastic bags and carting it through the house and out to the dumpster. I think it makes sense to remove the fiberglass because the paper backing, which for some reason is on both sides, is so dry and crumbling that I have a concern that it is a fire hazard.

Does this all make sense and what do you suggest?
 
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Old 03-29-14, 11:00 AM
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Details that are missing are, how much insulation are they proposing to add to the attic floor or rafters? And will it come up to the required code level. Remember, code is an absolute minimum.

Typically, the space needs to be partially heated when the rafters are insulated so that cold weather cannot lower the interior surface below the condensation level. Leaving the existing insulation in place means a colder roof.

Air sealing and insulating your ac and all ducts in the attic is necessary when insulating the attic floor.

If your ac unit is properly sealed and insulated, not just the pretty foil bubble wrap, then the need to spray the rafters goes away. If you get more bids from contractors to JUST add cellulose and air seal with some of the other details he mentioned I suspect the price will be much lower. My guess is he is inflating the cellulose because he likes to sell the foam (easier to make big bucks). Normally a foam job would be double the attic floor approach.

Just a few of the issues.
Bud
 
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Old 03-29-14, 11:07 AM
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He's proposing what's known as a hot roof. Personally, I'd remove the existing insulation, air seal as you have mentioned and then insulate the floor again.

Others will be along with varying opinions about this.
 
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Old 04-26-14, 09:21 AM
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Thanks to Bud9051 and Mitch17 for there comments.

Surely there must be others with some thoughts?
 
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Old 04-26-14, 11:31 AM
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esteve, which direction do you prefer, bottom of roof or attic floor?

Bud
 
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Old 04-26-14, 01:03 PM
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Bud9051,

I like the idea of insulating the bottom of the roof and the gable walls with spray foam and the removing the existing and worn out fiberglass insulation from the floor.

My main concern now is will I end up with heat from the living space escaping to the attic and effectively heating the attic? Or, will the attic just be a little warmer by not allowing the cold to penetrate the roof into the attic?

Same with air conditioning. Will the attic just be little bit cooler in the summer now by allowing the heat of the summer sun on the roof to penetrate the attic.

The contractor told me that the attic would be cooler in the summer and warmer in the winter by spray foaming the roof and gable walls.
 
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Old 04-26-14, 02:32 PM
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"cooler in the summer and warmer in the winter by spray foaming the roof and gable walls." is correct.

The success of a hot roof (insulating the underside) is using enough insulation. You are in a rather cold location and without checking, code for a sloped roof would be at least r-25 but check your local code. Since moisture will still find its way into the attic, there has to be some heat in the winter to be sure there is no condensation. Also, check to see if a ignition barrier is required. Be careful trusting what the spray foam contractor says, he sells spray foam.

The link below will give you a lot to chew on.
Bud

http://www.greenbuildingadvisor.com/...hedral-ceiling
 
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Old 04-26-14, 05:19 PM
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Thanks Bub9051!


The contractor did say that the spray foam needs to be coated with a fired retardant, which is also sprayed on like paint, which he would install a few days after the foam has fully dried.

It appears that I would need an R30 where I am located, but after reading the article at the link you provided I must say that this seems to be a more complicated question with a higher level of risk. The contractor did recommend using open cell spray foam, but after reading the article I now think that close cell spray foam is a much better choice and probably the only way to get a high enough R value.
 
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Old 04-26-14, 05:56 PM
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Open cell allows moisture vapor to pass through and condense on the cool bottom of the roof deck and ultimately rot it out. I personally don't think the full story is known about the consequences of a hot roof. In the south where it is common to have ac units in the attic and they do not deal with condensation issues as we do, a hot roof makes sense. But in a predominately cold climate, a standard vented attic is well proven with no hidden issues.

Where you do have ac up there, then maybe, but closed cell for sure.

Best
Bud
 
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Old 04-29-14, 01:20 PM
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I spoke to GAF, the manufacturer of my roof shingles, and they do NOT recommend spray foam being installed on the underside of the roof deck in the rafter bays unless the rafter bays have some venting. I am not sure about the gables on the house, which would also require spray foam to insulate them in conjunction with the underside of the roof.

GAF sent me a PDF, which is too large to upload, but if anyone wants a copy I can email it to you.

GAF recommends ventilating the roof rafter bays, as follows.

GAF recommends…
-Proper attic ventilation following the FHA/HUD 1/300 rule, which calls for 1 sq.ft. of
net free (open) soffit to ridge ventilation of per 300 sq.ft. of attic floor space.
-GAF does, however, recognize the emergence of unvented attic assemblies and recommends
that all code requirements be met and the manufacturer’s recommendations followed when
installing an unvented attic assembly.
-There are retrofit applications of sprayed-in-place foam insulation that allow for ventilated
attic assemblies. Where this type of application is installed, GAF’s recommendation of
proper attic ventilation amounts should be followed.
 
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Old 04-29-14, 05:03 PM
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GAF is actually giving their reduced version of the ventilation story. Here is a link from the source of the issue.
http://www.fsec.ucf.edu/en/publicati...CR-1496-05.pdf

Bud
 
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Old 04-29-14, 06:39 PM
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Thanks for the link Bud! Quite a bit of information in that document. Sometimes what seems like a simple question is not so simple. Not sure what I want to do yet.

By the way, I spoke to a spray foam manufacturer called Icynene and they offer a closed cell spray foam that has an ignition barrier built in so no ignition barrier need be applied on top of the spray foam. I like the idea of one less step.
 

Last edited by esteve999; 04-29-14 at 06:40 PM. Reason: typo
  #13  
Old 04-29-14, 07:14 PM
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Double check with your local code official to be sure they would accept that approach, the built in ignition barrier.

There are many problems with spray foam being debated and litigated, from installation quality and fumes during installation to entire homes being vacated due to those lingering chemicals. The defense from the foam industry seems to be, "if the installers are trained and follow correct procedures, then there will be no problems". My conclusion from that is, many installers aren't installing the foam correctly. But how are you and I supposed to know? Just Google "Spray foam insulation lawsuits LinkedIn"

Even with the ac unit up there, if you went with a traditional approach, air sealing and ceiling insulation the results would be good for many years with no concerns. Remember, many commercial buildings install their heating and air conditioning units on the roof so you can certainly seal and insulate one in your attic.

luck
Bud
 
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Old 04-30-14, 08:51 AM
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Thanks for the heads up on the spray foam potential health issues. I need to consider this, but I am now leaning toward the traditional approach of air sealing and insulating the attic floor.

Steve
 
 

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