# Re-insulate my vaulted ceiling for high performance



## Windows on Wash (Aug 30, 2011)

You planning on scabbing/furring down that ceiling for more depth?

9" of insulation isn't going to cut it in BC.


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## fdiddy (May 8, 2010)

I wasn't planning on it. The 9" is only at the eaves, it immediately starts increasing, and gets to 28" at the peak. I figured if I put 9" of roxul and then cover the joists with 1" of rigid foam board, I'll get to r37.75 just at the eaves. It will get much higher as I go up. The big concern I had was airflow. Do I need it, how much, which direction, how to implement it...


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## joecaption (Nov 30, 2011)

If you do not foam it then yes you need to add foam or plastic baffles which is going to eat up about 1-1/2" of depth before the insulation goes up. Also going to need a ridge vent.
Your area if I'm not mistaken calls for at least an R-50.
What condition is the roof in?
It's possible to go over the roof decking with SIP roofing panels to add R valve.


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## fdiddy (May 8, 2010)

There is already a ridge vent. If I added 1 1/2", how would I get to R50 without spray foam ? Two 5 1/2" roxul batts puts me at R44. And do I need to leave space above the insulation for airflow, or can I stuff the ceiling full to the brim.
Can't get above the decking, roof is fairly new and this is a strata building


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## fdiddy (May 8, 2010)

Here's a diagram of the framing:


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## Gary in WA (Mar 11, 2009)

Our codes allow a reduction in R-value at the eaves, check locally. You could always stack foamboard there, leaving an inch or so for venting (as so steep pitch); http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Are ridge areas open or is 2x4 blocking installed between each truss for assemble as pictured?

Gary


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## fdiddy (May 8, 2010)

There are 2 x 4s between the trusses running under the ridge.


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## Windows on Wash (Aug 30, 2011)

I would vent that roof as the guys are saying.

Fur down the framing for additional depth as you won't miss it that much, make your own 1-2" vent space with foam board, and then insulate.


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## Gary in WA (Mar 11, 2009)

Is that dark color on the plywood mildew? Just on the one side of roof- how much gap is next to the 2x block for actual venting of those bays? Are those bays on that dark side blocked at ridge by more of the 2x than other side? I would carefully cut the nails in one block and remove it for better exhaust venting at ridge. They shouldn't have fastened the ridge vent material to the blocking.... check one first.

With only 2900 HDD for your location, http://www.weatherstats.ca/winners.html?50 and Seattle here at 4800HDD, you would be in a Zone 4 Marine, and not very cold. Or, using our chart, R-38 in ceiling; http://energycode.pnl.gov/EnergyCodeReqs/index.jsp?state=Washington Check locally for code.

As you said, Roxul and fb on the truss bottoms will work. Use foam board for the first 2' for more R-value at the soffits.

Gary


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## fdiddy (May 8, 2010)

So I chatted with the inspector. Since I have one mushroom vent in the middle of the roof, all of the cavities need to be open below the top 2x4 so that air can flow over to the vent and out. He told me that R28 was sufficient, but I wanted to go higher. So I put 1 1/2" rigid foam all the way up, leaving enough room for air flow, to have a solid back to stuff the Roxul against. At the eaves, I was only able to add a 5 1/2" batt, but as the angle grew steeper, I stacked the insulation, all the way to 14 1/2" of Roxul backed by the rigid foam.
On top of everything, I will be putting a 3/4" sheet of EPS, just to break the joists' thermal bridge. All told, I'll be at R32.31 at the eaves, gradually increasing to R68.31 at the peak.
Hopefully, we'll be more comfortable! Thanks for the replies.


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## Gary in WA (Mar 11, 2009)

I wouldn't have used the poly but your codes call for it.... did you canned foam air seal the fb to stop outside infiltration to the poly- warm, moist air in your short AC running period? Moisture will condense on the insulation side of the poly ... without air sealing due to the temp. differences; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

Gary


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## fdiddy (May 8, 2010)

The poly is on the warm side of the insulation, and there is no AC, so there won't be any condensation. I hear you about no poly, but unfortunately the building industry is slow to learn new ideas, so I had no choice.


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