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Insulating attic in older home with no vapor barrier in the ceiling

Insulating attic in older home with no vapor barrier in the ceiling


  #1  
Old 02-25-21, 09:21 AM
L
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Insulating attic in older home with no vapor barrier in the ceiling

So I got a bit of a conundrum: I own an 87 year old home in eastern Canada (Newfoundland) with a hip roof, 2x4 ceiling joists and no vapor barrier in the ceiling (but the exterior wall do). This is not my work, but that of a previous owner.

The issue is that they only insulated up to the top of the joists with blown in insulation (looks like cellulose, but I'll be having it tested before I disturb it). It gets quite cold up here, and I know I'm likely losing a fair amount of heat through the ceiling as a result as the insulation is maybe R-10 total. What I want to do is replace the blown in insulation with fiberglass batt (2x4 R12), and then lay an extra layer on top of that to bring it up to R-40.

My question is as follows: I don't want to have to taken down the entire ceiling to add a vapor barrier (vapor barriers here are recommended to be on the inside, between the joists/studs and ceiling materials/drywall). Would using a faced batter for the 2x4 layer and then using unfaced batts for the top layer be okay? I would assume that the faced batts would essentially provide a vapor barrier (except the underside of the joists themselves wouldn't be covered). If it would be okay, what are the pros and cons of this method, besides being cheaper and easier?

My vision is very similar to what This Old House did here (except removing the old insulation): https://www.youtube.com/watch?v=fRVxdWaOJjk
 
  #2  
Old 02-25-21, 12:50 PM
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Paint and / or vapor barrier primers are all you need!
 
  #3  
Old 02-25-21, 07:39 PM
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you don't need a vapor barrier like sheathing or plastic for the ceiling... blown in insulation is fine and inexpensive compared to others. I live in Maine and had an energy audit and they raised my blown-in insulation from 6" depth to 12".
 
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Old 02-25-21, 08:53 PM
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Since you are located in Canada, and this forum is largely US based, I'm pretty sure that no US based answers by armchair quarterbacks will be accurate. Mine may not be either. Once you cross the border you have to play by completely different rules. And as far as I can tell, Canada is quite serious about using vapor barriers everywhere.

You will likely need to contact your local building department, assuming that exists up there, and find out exactly what your code says. Here is one example... just scroll down to 9.25.1.1 and do some reading from there on.

From what I can see by some light reading you need a vapor barrier and air barrier. And the Ontario code would allow you to leave your existing insulation (which, being so thin, has a negligable benefit), then place a poly vapor barrier on top of your existing 2x4 joists and insulation- PROVIDED you cover that vapor barrier with enough insulation that the vapor barrier stays sufficiently on the warm side of the added insulation. The idea is that if you put enough insulation on top of it, the vapor barrier itself should never get cold enough to get condensation on it.

For the benefit of US readers... By US energy star standards, 12" of cellulose is not enough to even reach a minimum recommended target of R-49, (in zones 5-8) based on the info at https://www.energystar.gov/campaign/...ation_r_values

See also IECC table 402.1.2.
 
larwilliams voted this post useful.

Last edited by XSleeper; 02-25-21 at 09:08 PM.
 

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