Cathedral Ceiling Insulation Options

[Circus]

I just skimmed over the responsives and maybe someone commented already. I didn't see any ice dams in your pictures. At least anything caused by escaping heat.
When the air temperature is near freezing and you have two feet of snow insulating the roof there's going to be a little melting no matter how well insulated. The question is how often. Once every five years or once a day. Rot needs a lot of soakings.
Vapor barrior faults cause water stains on your ceiling.

 

[Bret Chase]

when i insulated my cathedral ceiling with r30 paper faced insulation i was told in no way to put a vapor barrier or foamular directly against the paper faced insulation or i would run into issues. if any moisture were to develope it would be trapped and form mold. not that it cant be done but an air gap needs to be established via strapping? i get ice buildup around my chimney where i had to dead end the rafter mate vent so basically the roof has no way of staying cold there by drafting cold air from the soffit up to the ridge vent.

i may have made a poor choice selecting paper face insulation which painted me into that corner????

I don't use kraft paper faced insulation..... ever... There can only be a single vapor barrier in the whole system... otherwise you run into moisture problems...

 

[Bret Chase]

Thanks woodgeek. This is a manufactured home, basically a mobile built in some factory and hauled here and set on the foundation with a crane. The walls are 2x6 and I've pulled a few switch plates to check how they were insulated. Cavity is full and the walls never feel cold. I will pull a few more pieces of the soffit cover down and check the insulation where the ceiling meets the walls. I think I'm going to check every inch of where the walls meet the ceiling inside with my laser thermometer tonight when the temp drops to see if I can find any cooler spots.

It looks as if they built the entire outer shell of the house, drywalled the ceiling, and then added the interior walls where they wanted them afterward. I don't think there is any leakage from the interior walls if you meant that as well? Just guessing here as I'm no pro at this which I'm sure you can tell.

Ugh... modular housing... my brother has a modular, brand new in 2005... my house was built in 1865... he spent more than I did to heat his house with LPG than I did with K1.... K1 far more expensive than LPG (especially since he is getting the Selkirk rate....) and my house had NO insulation!. figure that one out...

BH, building a house as you've described is excellent from a fire prevention point of view... not always great from a energy savings point of view... pay close attention to where the modules were joined.... that is where you will lose the most heat.

 

[91LMS]

I don't use kraft paper faced insulation..... ever... There can only be a single vapor barrier in the whole system... otherwise you run into moisture problems...

with only having insulation and whichever material is chosen to finish, whether it be sheetrock, t&g, etc., are you saying paper faces is still a bad choice then?

 

[Circus]

I don't use kraft paper faced insulation..... ever... There can only be a single vapor barrier in the whole system... otherwise you run into moisture problems...​

You can lay a plastic barrior on the kraft paper side (interior) of kraft paper insulation. That still would only be one vapor barrior. Without all the holes.

 

[Bret Hart]

I just skimmed over the responsives and maybe someone commented already. I didn't see any ice dams in your pictures. At least anything caused by escaping heat.
When the air temperature is near freezing and you have two feet of snow insulating the roof there's going to be a little melting no matter how well insulated. The question is how often. Once every five years or once a day. Rot needs a lot of soakings.
Vapor barrior faults cause water stains on your ceiling.

No stains on the ceilings and thanks for pointing out the normal melting issues.

Ugh... modular housing... my brother has a modular, brand new in 2005... my house was built in 1865... he spent more than I did to heat his house with LPG than I did with K1.... K1 far more expensive than LPG (especially since he is getting the Selkirk rate....) and my house had NO insulation!. figure that one out...

BH, building a house as you've described is excellent from a fire prevention point of view... not always great from a energy savings point of view... pay close attention to where the modules were joined.... that is where you will lose the most heat.

Thanks BC. I spent some time with the IR temp gun and noticed that there was a bit of difference at the center of the house where they are joined. Going to pull the molding down and seal things up some when I get through the overload of work in the shop. Just been trying not to look at the ice since this is my busiest time of year.

 

[Bret Chase]

with only having insulation and whichever material is chosen to finish, whether it be sheetrock, t&g, etc., are you saying paper faces is still a bad choice then?

Using unfaced batts and covering the walls with sheets of 6 mil poly with TAPED seams is far, far better as a vapor barrier than kraft paper is. paper is far too easily damaged and detriorates fairly quickly within the wall space..

 

[Bret Chase]

You can lay a plastic barrior on the kraft paper side (interior) of kraft paper insulation. That still would only be one vapor barrior. Without all the holes.

in that case, you'd be better served pulling the faces off the batt.... otherwise you're going to end up with water trapped between the poly and the paper...

 

[woodgeek]

Just to be precise.....kraft paper is a lousy air barrier and vapor barrier (air and vapor both go around the paper). Properly detailed poly is a great air barrier and vapor barrier....but in most lower 48 climate zones a vapor barrier is not required (or can be bad) if a proper air barrier is in place. Intact drywall, with sealing of penetrations and framing gaps can be an effective air barrier while maintaining a small amount of (beneficial) drying capacity.

Torn/perforated kraft paper FG behind drywall is harmless, so long as there is no conditioned (humid) air moving in the cavity.

Poly is ok/recommended in Canada and (more or less) the US states on the canadian border.

 

[Bret Chase]

a vapor barrier is most definitely required by code and is the standard practice in the state of Maine.... whether it was done properly or not... is an entirely different story...

 

[woodgeek]

And one of these days....it will be dropped from the code.

 

[Bret Chase]

I don't see that happening... with the MUBEC... the push is towards buildings so tight that w/o makeup air... the occupants would die in a day or two...

 

[woodgeek]

And when they are airsealed (at the drywall, housewrap, etc), there is no need whatsoever for poly.

 

[Circus]

in most lower 48 climate zones a vapor barrier is not required (or can be bad) if a proper air barrier is in place.​

Wrong. Without a vapor barrior water condenses on the cold inner surface of the exterior wall and the cold exterior surface of the insulation. Shortly the insulation becomes soaked, the rafters drip water onto the ceiling and your building rots.

 

[Ehouse]

I've used a vapor barrier primer in bathrooms instead of poly.

 

[semipro]

And when they are airsealed (at the drywall, housewrap, etc), there is no need whatsoever for poly

Wrong. Without a vapor barrior water condenses on the cold inner surface of the exterior wall and the cold exterior surface of the insulation. Shortly the insulation becomes soaked, the rafters drip water onto the ceiling and your building rots.

This is actually fairly controversial. Conventional knowledge may be outdated.
These are really good articles on the subject which I strongly recommend those here read
http://www.greenbuildingadvisor.com/blogs/dept/musings/do-i-need-vapor-retarder.
http://www.greenbuildingadvisor.com/blogs/dept/musings/vapor-retarders-and-vapor-barriers

 

[begreen]

Wrong. Without a vapor barrior water condenses on the cold inner surface of the exterior wall and the cold exterior surface of the insulation. Shortly the insulation becomes soaked, the rafters drip water onto the ceiling and your building rots.

FWIW, our house is 88 yrs old. It has no vapor barrier and no house wrap. It was insulated about 16 yrs ago by a previous owner. When we did the remodel in 2006 a few walls were opened to make way for window or partition changes. Rodent damage we found in one area, but rot or moisture, no.

 

[woodgeek]

Controversial is a good way to describe it. Semi's links are good, I also like:

http://www.energyvanguard.com/blog-...54110/You-Don-t-Need-a-Vapor-Barrier-Probably

Moisture problems are due to the leakage of conditioned air, not diffusion through sheet goods. A wall that has air leakage through the cavity and a vapor barrier between the interior and the cavity is still wet (due to the air leak) and can't dry (b/c of the poly).

Scotty did the right thing putting poly in his ceiling b/c he was using T&G boards, he needed something as an air barrier (tyvek would have been good) but poly was ok since the roof was vented above the insulation....it could dry upwards.

 

[Bret Chase]

FWIW, our house is 88 yrs old. It has no vapor barrier and no house wrap. It was insulated about 16 yrs ago by a previous owner. When we did the remodel in 2006 a few walls were opened to make way for window or partition changes. Rodent damage we found in one area, but rot or moisture, no.

that's because your house most likely leaks air like a sieve... just like my almost 150 year old house does... all that air leakage carries the water away with it...

 

[begreen]

Exactly, there are no absolutes.

 

[RustyShackleford]

Im guessing the problem is not R value, but rather you have leaks ...

I'd guess the same. If it's a cathedral ceiling, you're not gonna get that much better than R30, maybe R38 (and you'd have to add bafflles). A little arithmetic will show you that's not worth much.

Your btus/hour per degree-fahreinheit for your 2000 sqft ceiling will go from 2000/30 to 2000/38, reducing that number by about 14. So over the course of a 5000 degree-day winter (typical for your area ?), you will save about 1.7 million btus or 500 kilowatt hours. Using electric resistance heat and a typical 10 cents per kwh rate, you'd save $50 a year (in heating). Use a heat pump or natural gas (or A/C, which is also a heat pump) and it's way less savings.

Of course there's also the issue of comfort (as was pointed out to me when I posted a similar calculation while wondering aloud whether to go with more expensive window glass), but as others have pointed out, air leakage has a vastly more important effect on comfort.

 

[welderboyjk]

I've got a question for the original poster, with all of the snow that I can see in the two roof pics you posted I'm guessing that your vents near the peak of the roof were covered, correct?
Absolutely NO insulation is perfect, the purpose of venting is to let the heat that does wander through the insulation out. If they were covered I can see why you had some ice. BTW it didn't look that bad to me either.

 

[Bret Hart]

I've got a question for the original poster, with all of the snow that I can see in the two roof pics you posted I'm guessing that your vents near the peak of the roof were covered, correct?
Absolutely NO insulation is perfect, the purpose of venting is to let the heat that does wander through the insulation out. If they were covered I can see why you had some ice. BTW it didn't look that bad to me either.

Just noticed that I missed this post. The vents were definitely covered after that snow in the pics but much of the 3 inch thick ice at the edge of the roof was there prior to that deep snow. The vents had been clear and working.

Thanks for all the help and for the reassurance that maybe it's not too bad after all.