Cathedral ceiling- cellulose vs spray foam?

[drz1050]

I'm in the process of making my attic into liveable space, so need to insulate the cathedral ceilings. Up until recently, I thought closed cell spray foam was the only way to go for a non-vented approach, but reading tonight there are articles saying that dense pack cellulose will also work.

I thought the whole idea of the closed cell/ non vented approach was that the insulation would also act as a moisture barrier- is this not necessary?

My roof is standing seam metal, so I'm not concerned about roof temps, but do care about possible sheathing rot.

Has anyone here gone the cathedral/ non-vented route? If so, what did you do?

 

[semipro]

In cold weather I think the important thing is where within your roof structure, including the insulation, the dew point occurs and what impact that may have.
If closed cell foam is used, the dew point temp should occur within the depth of the foam so moisture in contact with the inner foam surface would not condense.
If cellulose is used, condensation could occur within the depth of the cellulose since it has a relatively high permeability. The question then is does that condensation cause damage? I'm not sure it does though I don't like the idea of liquid water within cellulose. I can see where a vapor barrier below the cellulose would prevent that. On the flip side that moisture is not trapped within the cellulose so with not vapor barrier drying to the interior can occur.

That said, I suggest you get a real expert's opinion from Martin Holladay at greenbuildingadvisor.com.

 

[byQ]

I will be coming to insulating a cathedral ceiling at some point. So I have been seeking information, too. It sounds like a lot of contractors stuff the space in the ceiling with cellulose and seal it off (i.e. no air). Apparently this seems to work. Ya cellulose is vulnerable to moisture but if moisture can't get at it it doesn't matter.

 

[drz1050]

Thanks semipro! Yeah, that's my concern.. the cellulose getting wet. Go outside in wet clothes vs dry ones, and you'll find out real quick which ones insulate better... I'll try to look up and see what Martin says.

ByQ- yeah, that's another concern of mine. Contractors do a lot of things, and they rarely have long term results in mind. A true old- world quality contractor is hard to find.. If they can make an easy buck, they'll do it. In the process of a remodel here, I've ran through 4 contractors already. I'm down to doing things myself now, and just hiring muscle/ specialists as I need them. There are a couple contractors locally who I'd trust, but their prices are also outrageous. Hey, if the rich folks around here keep paying them, more power to em! Sadly there's a BIG gap between them and run of the mill contractors.

 

[iamlucky13]

What's the R-value per inch of dense pack cellulose? I know closed cell foam is relatively expensive, but the high R-value is certainly something to consider in its favor.

 

[byQ]

Ya I hear ya. You never really know if a contractor knows what they are doing. Going by the lowest bidder isn't always a good idea. References and watching the crew work on another similar job are good ideas. I had a crew pour a slab - two adults and three 16 year olds show up - basically a father his son and 2 friends of his son, and another dude's first day on the job. They show up with the concrete truck on the way and there gas powered leveling machine ready but with no gas! I scramble and find a new big 5-gallon gas can 2/3 full.

The Dad is yelling at the other 4 non-stop, "..you idiot...are you dumb....do it like this....etc...". The new guy (who has concrete experience) threatens to quit on the spot, and tells the boss "..to shut the **** up!" I'm starting to panic. I grab a shovel and prepare for the worse.

I say to the boss, "..shouldn't we lay the metal mesh into place before the concrete truck gets here?" He says, "No, we'll put it in from the top." At this point I should have overruled him. The truck comes, pours for a while, and I hear, "...Mr. we forgot to put the mesh in and now the concrete is setting up ...." Luckily, I got 3 of the 6 pieces of mesh in on the other side.

They didn't order enough concrete (of course). They (we) finish after hours. They leave. I notice my large gas can missing - the one I had lent them to use for gas that they forgot to bring. I called and left a message about the gas can - never heard back from them. Afterwards I realized I picked the wrong contractor.

 

[DBoon]

If closed cell foam is used, the dew point temp should occur within the depth of the foam so moisture in contact with the inner foam surface would not condense.

I'll second that, and add that you should also consider how the house total vapor barrier will be located and what will be considered the conditioned space of the house. If you are going to insulate the attic ceiling, you should consider (I think this goes without saying) insulating the entire attic gable walls, and ensure that you have a good vapor barrier down through to wherever the previous vapor barrier left off (presumably the ceiling of the occupied floor above it. Closed cell foam is a pretty good vapor barrier, but if it shrinks in the cavity moisture will travel through to the roof sheathing, and (I believe) get trapped by the metal roofing. Therefore, you might want to consider 1 or 2" of foam board under the attic rafters to ensure that you have a good insulating surface not prone to shrinkage failure and a vapor barrier there as well.

I second that it would be worth getting the opinion of a building scientist (separate from the spray foam contractor) so that you can make sure the install is done in a manner that will work over the long term.

 

[drz1050]

What's the R-value per inch of dense pack cellulose? I know closed cell foam is relatively expensive, but the high R-value is certainly something to consider in its favor.

Dense pack is ~4.0 per inch, closed cell is 6 per inch.

 

[drz1050]

I'll second that, and add that you should also consider how the house total vapor barrier will be located and what will be considered the conditioned space of the house. If you are going to insulate the attic ceiling, you should consider (I think this goes without saying) insulating the entire attic gable walls, and ensure that you have a good vapor barrier down through to wherever the previous vapor barrier left off (presumably the ceiling of the occupied floor above it. Closed cell foam is a pretty good vapor barrier, but if it shrinks in the cavity moisture will travel through to the roof sheathing, and (I believe) get trapped by the metal roofing. Therefore, you might want to consider 1 or 2" of foam board under the attic rafters to ensure that you have a good insulating surface not prone to shrinkage failure and a vapor barrier there as well.

I second that it would be worth getting the opinion of a building scientist (separate from the spray foam contractor) so that you can make sure the install is done in a manner that will work over the long term.

Oh yeah, the walls will be insulated as well for sure. There is no old insulation. There was some in parts of the ceiling between floors, none in other spots. The stuff that was there (blown-in fiberglass) has been ripped out- that was fun. I'm almost positive I want cellulose in the walls, but I'm open to suggestions there too. Next year I'll be getting new siding, before that goes on I'll also have foam board placed on the outside of the house. Just have 2x4 walls here, so not a ton of room for insulation there.

 

[drz1050]

I have some foil-faced tuff-r foam boards, and have considered putting that up against the sheathing, then filling the rest of the space with cellulose... but how would I ensure a tight fit against the sheathing? There's sure to be air pockets left when using a stiff board vs spray foam that will fill all the nooks and crannies... or are those little pockets not worth worrying about?

 

[cableman]

I saw a Holmes on homes episode where they put the pink air baffs against the roof sheathing 1st, then sprayfoamed over that. I thought the air channel wasnt needed with spayfoam, apparently it is to them.

 

[drz1050]

I saw a Holmes on homes episode where they put the pink air baffs against the roof sheathing 1st, then sprayfoamed over that. I thought the air channel wasnt needed with spayfoam, apparently it is to them.

Air channels aren't needed with closed cell foam, maybe they were spraying the open cell on the show?

From all the reading and such, looks like I'm going to go the closed cell route for the roof, and cellulose for the walls. There are reports of dense pack cellulose being used successfully in cathedral ceilings, but also reports of disaster... In this case, I'll play it safe, or at least the safest I can for an unvented roof.. thanks for all the help fellas!

 

[Buzz Saw]

Why not use the baffles and vent the ceiling? Lower efficiency?

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[drz1050]

A few reasons... I have 2 skylights, so those rafter spaces can't be vented. Also, my rafters are only 2x6, so there isn't much room for insulation as it is. In this case, 1" makes a difference. No matter what I do, I can't fit enough insulation in there to be up to modern code, but this will get me the closest.

If I was to build a house from the ground up, I'd definitely have a vented roof, with 2x12 rafters.

 

[Buzz Saw]

What is current code insulation values?

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[drz1050]

What is current code insulation values?

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I'm in zone 5, so they recommend R-49.

http://www.greenbuildingadvisor.com/blogs/dept/musings/overview-2012-energy-code

 

[iamlucky13]

2x6 rafters in NY sounds to me like a strong argument in favor of closed cell foam to get as much insulating value as possible.

 

[DickRussell]

Here is the GBA link you want: http://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling

 

[iamlucky13]

This is Washington specific, but that mainly applies to the required R-values. Pages 66-72 might be helpful. It looks similar to what's in the Green Building Advisor article:
http://www.energy.wsu.edu/Documents/entire_guide.pdf

 

[drz1050]

Thanks fellas! I've been getting quotes from spray foamers around here this week.. 2 quotes in so far, waiting on one more to be e-mailed, and have another company sending a rep tomorrow.

Any experience in these forums regarding Icynene vs Pro Foam?

 

[blades]

Pro foam- brand name/franchise not the name of the particular material- they do list a closed cell product.
Icynene- particular product type

 

[semipro]

Ya cellulose is vulnerable to moisture but if moisture can't get at it it doesn't matter.

Roofs leak sooner or later though. Even if the water can't get in from inside it will eventually make it in from the outside.
In my mind that tends to disqualify any insulation that would soak up water in roof assemblies.

 

[drz1050]

Pro foam- brand name/franchise not the name of the particular material- they do list a closed cell product.
Icynene- particular product type

Profoam is the manufacturer of the material, like Icynene is. Foametix is another, but I haven't talked to any sprayers here yet that use their stuff.. 2 quotes from icynene so far, 2 from profoam.

http://www.profoam.com/

http://www.icynene.com/en-us

http://foametix.com/

Was wondering if anyone here had first hand experience with either.

 

[DBoon]

I used the Icynene open-cell on a basement install. If I did it again, I would go closed-cell foam - higher R-value and less risk of moisture migration below grade (though this hasn't been an issue for me at all, best I can tell/smell).

I think if you look at the Green Building Advisor article, they say they don't recommend open-cell foam for a attic ceiling - not enough R-Value and it is vapor permeable.

 

[Buzz Saw]

Profoam is the manufacturer of the material, like Icynene is. Foametix is another, but I haven't talked to any sprayers here yet that use their stuff.. 2 quotes from icynene so far, 2 from profoam.

http://www.profoam.com/

http://www.icynene.com/en-us

http://foametix.com/

Was wondering if anyone here had first hand experience with either.

Had my pole barn sprayed this spring with Icynene. The barn is 40x60x14' walls. I have 3 overhead doors. Two 9x10 and one 12x14. The doors aren't that tight(yet). 4 windows and one entry door.

My family is currently living in the barn while we are remodeling our house. This summer we ran three window air conditioners and kept the barn at 72°
all summer. Our electric bill went down $20 living in the barn.

Haven't had a winter in here yet but so far really happy with it so far.

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