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I am building a log home in the Black Hills SD. I am using tongue & groove over the exposed rafters, then vapor barrier (30 lb felt), then 6" rigid foam insulation, then sheathing, felt and shingles. Roof pitch is 12/12. This is a non vented roof system. Couple of questions: I'm new to this, so do you see any problems with this system? Someone suggested two vapor barriers might be a problem. Second question: How do I keep the roof dry while building...will the felt be enough or do I need to use tarps..ect...Thanks for your help.
 

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I can see moisture getting trapped between the two vapor barriers but wait for the roofers input.
 

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My biggest concern in this scenario is always how do we keep the condensation form ruining the ceilings.

I do not see ant problems with the system itself, we see it a lot. The moisture between the vapor RETARDERS (they are really barriers) should not be a significant factor unless the roof leaks. Maybe not even then.


I say...if it was my house, I would not have any worries about the system itself.

You will want to get the roof on as soon as it is tongue and grooved, though. Felt is pretty flimsy to rely on for protection of that expensive ceiling for anything longer than a couple of days, in my opinion.
 

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Code requires ventillation! (1:300 min) Leave an air space between the top of the ridgid insulation and the sheathing...vent that space at eaves and ridge. Don't use 30# for the first VB. Not good enough, too many laps. Use 6mil visqueen. Seal it well at all penetrations (vent pipes and light cans).
Jim
 

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You could easily vent the interior gable. Code does not require venting roof assembly components in direct contact with each other.
 

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IMO, leaving a vent space between the insulation and the sheathing, then venting is the best way to go.
I have required authorized individuals to 'sign off' on the sytem if it doesnt have venting, if I am to apply a roofing sytem on it.
The system that initialy was described, I have seen problems with, though to be honest I didnt know the entire assembly details.
What I have seen with warm 'compact' roof assemblies is deterioration of the sheathing at the ridge mostly,also the fasteners being attacked and corroded from the moisture inside the assemblies.
 
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