I'll check that vid. Been dealing with some fam issues lately. Can cellulose (I assume spider since Dana keeps referencing that product) be used in a cathedral ceiling assembly? Again my whole roof is all cathedral. I will also try to contact some Spider contractors in the Chicago area. I have contacted the OEMs website twice now, no response. So that kinda bugs me.

I found this for JM Spider:

http://www.specjm.com/files/pdf/t07-016jmspideroverheadapplicationv2.pdf

Seems they recommend a vented cathedral for non-Zone 1/2 areas (I am Zone5)

So what if I do this:

1) metal roof (3:12 to 4:12 slope)
2) #15 felt
3) water and ice around perimeter (required)
4) structural sheathing
5) 1.25" air gap (due to the rigid EPS item #6)
6) ripped 1" Type2 EPS to 1' 11-7/8" width (1/4" wider than btwn webbings) wedged between TJIs (R4)
7) JM Spider 11.5" thick (~R46)
8) vapor retarder membrane, gypsum with latex paint

R4 + R46 = R50 cathedral assembly with minimal risk of shrinkage and the airgap will provide drying to exterior. The EPS will minimize air movement through the spider. What do you think of that?

JM Spider is blown fiberglass, not cellulose.

Applegate is one manufacturer of cellulose insulation. Here is what they have to say about cathedral ceilings:

http://www.applegateinsulation.com/Applications/Construction-Conundrums/default.aspx

and

http://www.applegateinsulation.com/...49234.aspx

Thanks. It looks like they have a vapor permeable membrane on the exterior and i have a metal roof so not sure if this is right for me. They also state tominstall it at 3.5pcf and at that pressure it wants to expand outward. So how is this installed in a cathedral ceiling with no membrane on the interior side? I will ask the OEM, thanks fornthe link. So JM Spider is not an option for me you think?

Well I'm being told by installers "Cellulose is possible but netting would be risky. The depth and width will create too much weight between the rafters, causing the netting to sag. It would be possible to insulate with cellulose if the drywall is hung first, and an area is left open to access rafter cavities. The only other option would be 2 part spray foam."

but two part spray foam is expensive.

another quote suggested this:

firestop penetrations from level to level
insulate windows and doors with low expansion spray foam
block rafter cavities with rigid foam board and spray foam perimeter to prevent wind wash
install air baffles for required ventilation
2x6 exterior wall cavities with wet spray cellulose to R-21
14" rafter cavities with fiberglass batts to R-38 ***********(I don't like this one...)
basement joist cavities to be insulated with 2 part closed cell foam (2"min.)

we typically do ceilings after the drywall is hung; whats the problem with that?

I suppose nothing aside from if it costs more...I will talk to those guys. It's a little early admittedly but I want to get this insulation nailed down...

no reason it should affect the cost.

Cellulose can be wet sprayed vertically, Of you may be able to spray or dense pack it in from above.

Posted By arkie6 on 12 Feb 2014 03:41 PM
JM Spider is blown fiberglass, not cellulose.

Applegate is one manufacturer of cellulose insulation. Here is what they have to say about cathedral ceilings:

http://www.applegateinsulation.com/Applications/Construction-Conundrums/default.aspx

and

http://www.applegateinsulation.com/...49234.aspx

Thanks for posting that I subscribe. As I stated on DaveJJ cathedral thread, it makes no sense to vent to the elements. Now I see the codes were set up for FG and do not account for other materials. Roxul is another great dense filler that has better properties than cellulose in this application if cost prohibiting in your area. I will not use a vapor retarder on the ceiling interior and let it dry this direction, safegard if home owners have no humidity control and my code requires it if unvented. I like advantech as a deck and it insul board keeps the thermal bridges down and provides a capillary break to the roof membrane (shingles, metal, wood) better than felt since water can not get to the bonded surface(OSB-WRB) and it acts as an air/moisture barrier sealing in the exterior of the assembly and evelope.

TLP, I will have a vented channel regardless of what anyone says. My reasonings are water will eventually get in and insulation against roof sheathing is just a bad idea when it comes time to repair the roof.

I have TJI14s. I will be installing a layer of 1/4 or 1/2 in OSB on the underside of the top plate of the TJIs so the top 1-3/8" is a vent and blow cellulose against the rigid second layer of sheathing for R45. The internal barrier will be intelloplus. So there will be drying both ways.

Applegate's hedge words are telling - "in nearly every climate" and "it may not need a vapor barrier". Basically they argue that with cellulose you can get by without - in most cases.