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Old 06-08-2013, 10:02 PM   #1
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Location: Fort Smith, NWT, Canada
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Major Ventilation Issue


I have having a serious issue with frost buildup in my roof over the winter. I have vaulted ceiling with no attic space. The construction of the roof from inside out is:

1) Drywall
2) Vapor barrier
3) Roof joists (3.5/12 pitch) with pink insulation including a 1.5" pink fibreboard on the upper layer. Total insulation thickness is 11".
4) 2x4 strapping purlins on top of the joists on their flat side - running horizontal to the roof.
5) Plywood sheeting
6) Ice barrier/Tar paper
7) Shingles.

So the only ventilation are 1.5" by 14.5" (I believe it is about 16" centers) space that runs 40' from one side of the house to the other. The roof is a simple roof with two gable walls on a typical 26'x40' bungalow. So with so little air space, condensation builds up all winter and then in the spring it pours in around my windows and any small gaps in the vapor barrier.

So as I see it I can try two things

1) Remove all ventilation and airspace. As I understand it, this won't work unless I remove all the insulation since pink insulation should not be underneath rigid insulation.

2) Add more vent space. Presumably by ripping off the shingles and sheeting and then building a 2x4 framing (on edge) and rebuilding the roof on top of that. Then the question is do I just use a ridge vent or how do I frame it to still allow lateral ventilation with a couple of chimney vents or "whirly birds". Will a ridge vent manage with snow cover (we have snow and little wind here so there is typically a foot or two of snow across the entire roof.

The other thing to consider is I live in a cold climate so it is winter for about 6 months and we can have extended temperatures down to -40. I also run a wood stove with puts the interior ceiling temperature at up to +30 celcius.

I just reshingled the roof a couple of years ago so it is a real kick in the can to have to pull it all off and start over so I want to make sure I do it right. Any suggestions are greatly appreciated.

SubarcticGuy

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Old 06-08-2013, 10:47 PM   #2
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Location: Hartfield VA
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Major Ventilation Issue


Please go back and add your location to your profile.
Ya that's to bad you just redid the roof, could have been done with SIP roofing panels.
Was storm and Ice Shield used on the lower edges of the roof?

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Old 06-09-2013, 12:49 AM   #3
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Location: Fort Smith, NWT, Canada
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Major Ventilation Issue


I am right on the 60th Parallel on the border between Alberta and the Northwest Territories. Storm & e shield was used on the lower edges and is actually covering over 2/3's of one side because they were actually out of tar paper at the local building center when I redid the roof.
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Old 06-10-2013, 04:26 PM   #4
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Major Ventilation Issue


You are in some extreme climate there so unfortunately, you insulation and air barrier approaches need to be equally as extreme and comprehensive.

You are, as you have noted, not there.

You are going to be ripping off the roof or ripping down the drywall so you will have to decide what you are more comfortable with enduring at this point.

The lack of insulation performance can be remedied from the top down or bottom up but both would entail getting rid of the filter (i.e. fiber) glass.

Let me know what side you want to tackle and that will determine what is best. Taking the selective demo of either the ceiling or the roof out of the equation, both option would be about the same in terms of expense and neither will be cheap.

Feel free to ping me either way to discuss.
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Old 06-11-2013, 09:46 AM   #5
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Major Ventilation Issue


Quote:
Originally Posted by Windows on Wash View Post
You are in some extreme climate there so unfortunately, you insulation and air barrier approaches need to be equally as extreme and comprehensive.

You are, as you have noted, not there.

You are going to be ripping off the roof or ripping down the drywall so you will have to decide what you are more comfortable with enduring at this point.

The lack of insulation performance can be remedied from the top down or bottom up but both would entail getting rid of the filter (i.e. fiber) glass.

Let me know what side you want to tackle and that will determine what is best. Taking the selective demo of either the ceiling or the roof out of the equation, both option would be about the same in terms of expense and neither will be cheap.

Feel free to ping me either way to discuss.
I will likely be going through the roof. I am also planning an 20' addition off the back next spring that will affect about 25% of the roofline anyway. I think I will have to add vent space above, I am just trying to figure out how to frame it so that I can get some cross flow underneath. I don't think I can rely on a ridge vent since it will be snow covered most of the year.
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