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Old 04-13-2014, 08:01 PM   #1
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Closed cell foam enough?


I have a fairly new cabin in the Colorado mountains. It is a hunting/fishing cabin that was not built to be heated year round. However, I would like to use it year round.
The ceilings are tall cathedral ceilings. The roof is framed with 2x10s, and then sprayed with 2.5" of closed cell foam. I figure this gives me about R-15 from the closed cell foam and maybe another 1 or 2 from the air space between the foam and sheetrock.
I am thinking about cutting holes at the highest point of the ceiling between each rafter and blowing as much cellulose as I can in the space between the foam and the sheetrock. There would still be empty places near the ridge where the holes were cut out.
Do you think this is worthwhile? Its a lot of patchwork etc. Closed cell foam is super efficient, maybe I wouldn't even see much of a difference? Thanks!

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Old 04-14-2014, 11:13 AM   #2
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Closed cell foam enough?


Hey Learyw, I always recommend 2"- 3" of closed cell foam when insulating cathedral ceilings. It's going to give you an R-Value of 14-21, stop air leakage, and resist moisture penetration. Our company's foam also prevents mold growth.

It's perfectly fine to have air space between the foam and the sheetrock. You can certainly add cellulose if you want to bulk up on R-Value, but it isn't necessary because the foam is so effective.

When are you planning to insulate?

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Old 04-14-2014, 11:25 PM   #3
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Closed cell foam enough?


If in the mountains, in Zone 7- that little bit of SPF will not be enough. Neither will adding cellulose, in this application- to prevent interior-side of FB; condensation. Your State is dragging-it's-heels with codes, still under the 2003 codes; http://www.energycodes.gov/adoption/states

Find Zone by county; http://publicecodes.cyberregs.com/ic..._11_sec001.htm

Code amount required; http://publicecodes.cyberregs.com/ic..._11_sec002.htm

SPF/FB (air-impermeable) to prevent condensation; eg. R-30, with remainder in whatever to R-49; http://www.buildingscience.com/docum...rchterm=attic+

In for a penny, in for a pound, holes are easy to patch... esp. when we tell you how and you DIY, lol.

Gary
PS. Welcome to the forum, to the both of you!
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Old 04-15-2014, 07:09 AM   #4
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Closed cell foam enough?


As long as the CC SPF was put in correctly and you don't have any pull back, the vapor control and air barrier should be intact.

If that if true, and only if that is true, you can dense pack the ceiling.

If there are issues with that, dense packing the ceiling can be a disaster.
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Old 04-15-2014, 02:03 PM   #5
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Closed cell foam enough?


Thank you for the responses! The closed cell foam was installed very well and it is a solid barrier. I certainly can appreciate what a bad combo cellulose and moisture would make.

I guess the root of my question comes from the data I copied below. I have had several people tell me that 2" of CC foam actual performs way better than the listed R-14 or so. It has been awhile since I've taken thermodynamics but the numbers below make an interesting point. If in fact 2" performs as well as R-40 fiberglass, I dont think there would be much reduction in energy use by adding cellulose. Let me know what you think!

Fiberglass insulation…….R 3.2 per inch
32% Efficiency Rating
3 inches in a 2X4 wall with a 32% ER is equivalent to R11.2
Collects moisture


Cellulose insulation……...R 3.5 per inch
36% Efficiency Rating
3 inches in a 2X4 wall with a 34% ER is equivalent to R 12.74
Collects moisture


Open cell foam insulation…….…R 3.5 per inch
44% Efficiency Rating
3 inches in a 2X4 wall with a 44% ER is equivalent to R 13.72
Collects moisture


Closed cell foam insulation….….R 7 per inch
92% Efficiency Rating
3 inches in a 2X4 wall with a 92% ER is equivalent to R 63.7
2 inches in a 2X4 wall with a 92% ER is equivalent to R 40.18
1 inch in a 2X4 wall with a 92% ER is equivalent to R 20.09
Does not collect moisture

Source: alpinefoam
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Old 04-16-2014, 12:04 AM   #6
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Closed cell foam enough?


They must have both been SPF salesmen. Most SPF is rated at around 6.5 per inch, maybe they are figuring before aging rating; http://www.sprayfoam.com/spps/ahpg.cfm?spgid=6 I could be wrong, though. I'd be interested in how they find the ER percentages... do you have a chart?

I doubt they mean a higher R-value as those are pretty standard, except FG is rated in a closed, six-sided container, not near as in a house. Each insulation has it's good/bad, read it all- esp. comments below; http://www.finehomebuilding.com/item...ean-insulation

I would add more SPF to get your cavity to zero chance of condensation, cellulose won't insulate the roof sheathing enough- you need more SPF- at least to code minimum (as I stated and linked earlier); http://www.buildingscience.com/docum...-dont-be-dense

http://www.buildingscience.com/docum...r-all-climates

Gary

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