DIY Home Improvement Forum banner

6mil plastic under ridge vent?

2K views 10 replies 2 participants last post by  aquasport17 
#1 ·
I am insulating and sealing a brand new cathedral ceiling. After installing R-38C I plan to staple/tape up 6 mil plastic sheeting for vapor barrier.

My question: Do I use a continuous sheet right up and under the ridge vent and over to the other side? Or do I stop the plastic short of the ridge vent on each side?

I'm guessing I am going to go right under and over.

Thanks!

Jeff
 
#3 ·
It's in Southern Vermont. Owens Corning R-38C High Density fiberglass batts are going into 2x12 rafters (I understand the code is R49 but that's not my question). I'm simply wondering if I should seal the ridge vent by running the plastic up, under and down the other side, or only run it up TO the vent.

Note that there is about a 3 foot crawl space under the ridge, so the cathedral doesn't go right to the top.

I am also considering rigid foam over the 2x12 rafters instead of plastic sheeting to get me a little more R. Depends on budget.

Jeff
 
#5 · (Edited)
Rigid foam may be out of the budget. This is a part time getaway house - but I still want to do it right, and do it within budget. I could add 1" R5 foam possibly.

My question still remains. Do I run whatever vapor barrier I use all the way up and under the ridge to seal off the ridge vent from the living space, or not?

Maybe I will use the rigid foam up to the attic area and over the flat part of the cathedral, leaving the higher section above the ceiling with R38C in the rafters, and R30 in the small attic area? The top looks like this: /-\ with the small space above the cathedral about four feet high to the ridge.

J
 
#7 ·
It's traditionally vented with a ridge vent and soffit vent. I plan to use 1" baffles between the R-38C and the roof deck.

Yes I agree the 1" rigid foam is the way to go but it's 10 times the cost of plastic for only an R5 increase.

Plus, I think I would need furring strips to secure my tongue and groove to the rigid foam - adding more time and expense.

I'm undecided.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top