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Cathedral Ceiling Insulation Options

Post in 'The Green Room' started by Bret Hart, Jan 3, 2013.

  1. Bret Hart

    Bret Hart Member

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    Just wondering what would be the best option for adding to the R-value of a cathedral ceiling in a modular home or just improving it's performance. It is just under 2000 sq. ft. and appeared to be fairly well insulated and vented. I don't see any obvious openings from the inside for heat to escape at any kind of volume. When I put the new chimney through the ceiling, I could see what looked like at least 10" of fiberglass batts. so I'm guessing at around R-30. Ice dam build up is more than expected.

    It has 10 or 12 of these vents: http://www.lowes.com/pd_157025-52595-PRV61BL_0__?productId=3284536&Ntt=roof vent near the ridge only they are 12"x12" and the eves are vented from end to end of the building.

    I am hoping that my only option isn't removing all the drywall and starting over.

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  2. jharkin

    jharkin Minister of Fire

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    Im guessing the problem is not R value, but rather you have leaks letting conditioned air into the ceiling. Do you have any recessed lights in that area?

    I had a similar situation, cathedral ceiling over kitchen with R-32 fibergalss and vent space and a continuous ridge vent that still ice dammed.

    I found the problem was 4 old style non-airtight, non-IC can lights in that ceiling with 65watt floods that were leaking massive heat into the ceiling. I replaced them with airtight/IC cans, caulked them tight and replaced the 65w bulbs with 15w LEDs. Ice damming solved.
  3. Bret Hart

    Bret Hart Member

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    There aren't any recessed lights anywhere in the home and the ice dam is the same from end to end on both the front and back of the house. Maybe I should remove the molding where the walls meet the ceiling and look for gaps there or just plan on caulking it all and replacing the molding. I do agree that there is excess heat getting up there somehow.

    This is what the ice dam looked like before it warmed up a bit last weekend and I carefully removed it after the water got between the ice and shingles.

    Attached Files:

  4. ScotO

    ScotO Guest

    What kind of vapor barrier do you have in that ceiling? I just installed two cathedral ceilings in my living room project, using tongue and groove pine, air-tite recessed light cans and a good heavy plastic vapor barrier. The vapor barrier is taped at all seams and where staples were ripped through, etc., and sealed with hi-temp RTV around the can light openings. I can tell you that the vapor barrier makes a HUGE difference. I used a total of R43 in that ceiling, with both baffles at the eaves and a ridgevent at the peak. I am leaking a miniscule amount of heat/vapor through some spots in the can lights, I plan on sealing those spots with high temp silicone......but I have NO ice damming issues whatsoever, the roof still has snow (no ice) on it and I've had the fire burning out there pretty much nonstop since Thanksgiving...
  5. semipro

    semipro Minister of Fire

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    ScotO likes this.
  6. GaryGary

    GaryGary Feeling the Heat

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    Hi,
    This is not a great solution, but it does work pretty well -- at least until you can work out something better.

    Get a roof-rake and use it to pull the snow off the roof after snowstorms.
    http://www.roofrake.com/ several outfits make them.

    Its surprisingly fast to use and it definitely reduces ice dam problems. Since you don't have the snow on the higher parts of the roof melting, running down, and then freezing at the edge of the roof to add to the dam.

    Gary
  7. Bret Hart

    Bret Hart Member

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    Thanks for the tips.

    Gary,
    I was hoping to stay away from the roof rake because of the work involved. We get a lot of lake effect snow here and I'm thinking I might look like a body builder by spring. The "Warden" might like that though instead of my beer belly.

    Scott,
    Now that you mentioned it, I don't remember seeing a vapor barrier up there when installing the chimney and cathedral box. Might have just missed it though because I didn't specifically look for it. If it's not there, I'll bet that's one of the biggest issues. I will find a way to get my mechanics scope up in there and have a look around.

    By the way, awesome job on your hearth build.

    Semipro,
    Thanks for the links. I will be reading them thoroughly to see what I can do.
    ScotO likes this.
  8. jharkin

    jharkin Minister of Fire

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    Even if you have no vapor barrier don't loose hope. I don't have one and have been able to eliminate a lot of the ice with careful sealing and blown in insulation retrofit. The only part of my roof that still gets any meltis the area over the section of storage attic. In this area I have the internal chimney for the stove, a bath ceiling that didn't get enough insulation and a leaky attic door. I'm working on insulating and sealing those now.

    I'm no expert, but I think with some careful work you should be able to limit leakage enough to keep the ice manageable without gutting the attic. You might always have some but at least not enough to cause damage (assume the roof has ice and water shield).
  9. 91LMS

    91LMS Member

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    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????
  10. Bret Hart

    Bret Hart Member

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    That's the part that worries me. There isn't any attic space to speak of.
    At the outside walls, there is about 6 or 8 inches from the top of the insulation to the bottom of the beams that hold the roof sheathing and at the ridge it looks like there is about 12 to 14 inches. No way to get in there without removing the drywall ceiling which would be a job I'm not interested in. Not sure if insulation could be blown in all the way to the ridge from the soffit openings as I've never done anything like that.
  11. ScotO

    ScotO Guest

    After extensive.research prior to my install, I chose unfaced insulation (R30 above the truss, R13 between them), and used the good, sealed, plastic vapor barrier for total coverage. With paper faced insulation, you still get a lot of vapor loss (from what I read on it). You are correct about NOT installing a plastic vapor barrier over a paper faced insulation.......the double vapor barrier will trap moisture and definitely lead to mold problems. My ceiling is properly vented, baffled, and so far I'm impressed with the performance of it. It really pays to research your options before committing on a procedure. Every climate has pros and cons in regards to the different installation methods.
  12. Bret Hart

    Bret Hart Member

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    Your post just made me remember that the insulation up there has the paper face so I guess there is a vapor barrier.

    This isn't looking good.
  13. ScotO

    ScotO Guest

    like Jeremy said earlier, don't lose hope. There might be another way around this.

    Worst case scenario, you MAY have to take the ceiling down (again, worst case scenario). How big of a space are we talking about here? Any recessed (can) lights in this ceiling? Any other leaky places (trap doors, bathroom ceiling vent dans, etc.)?

    Have you considered maybe installing heat tape along the eaves to help keep the ice from damming up? That may possibly be an option (if all else fails and you do not want to tear that ceiling out).
  14. Bret Hart

    Bret Hart Member

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    There are 2 bath vents and nothing else is recessed. No trap doors either. I am thinking I should seal all the light fixtures, might have been done poorly when built, since this could add to the problem.

    The space is fairly small in volume (see post #10) but it runs the entire length of the house which is around 70 or so feet.

    The thing that gets me is, I would have thought the ice dam would be worse in the areas of the vent fans or the chimney with the extra localized heat. It isn't though. The ice dam is almost dead even the entire length of the roof on both the front and back side.

    I have thought about the heat tape but spinning the electric meter faster isn't very appealing. Might have to do it though. Starting to think that a few feet of flashing up from the drip edge in the spring may be someplace to start.
  15. woodgeek

    woodgeek Minister of Fire

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    If the cath ceiling is drywalled completely, then there is no airflow, and the vapor diffusion through drywall+paint is NOT going to be a problem with a vented roof. The ice damming IS telling you you have conditioned air flow (or an insulation gap) into the ceiling cavity, but it is not happening because of vapor diffusing through drywall (or lack of a 'vapor barrier').

    More likely, there is an air path between the wall cavities and the ceiling, or not enough insulation right at the corner due to some detail of the framing. The Worst case scenario is not a whole roof full of mold (the venting will prevent that), or a complete tearout of the entire ceiling. The choice is either live with the ice dams (lots of folks do), rake or install a heat rope along your eaves. For a permanent and passive fix: tear into the corner (either the wall or the bottom of the ceiling) and seal the paths, or beef up the insulation with spray foam, and then re-drywall. JEremy's suggestion of blowing some AIR retardant insulation into the wall cavities would help, if your walls needed that also.
  16. Bret Hart

    Bret Hart Member

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    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.
  17. semipro

    semipro Minister of Fire

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    ...Or insulate above the existing roof as I pointed out earlier which is widely promoted by many experts such as those at BuidlingScience.com, a resource commonly referenced here. If you do this (correctly) you get:
    • Less overall conductive heat loss through the roof and prevention of ice damming
    • Less overall convective heat loss through the roof because venting is not required (and should be removed)
    • Prevention of moisture related issues in the existing roof structure because the dew point is moved to a point within the foam insulation added to the roof. So condensation of any moisture making its way into your ceiling does not form on:
      • the drywall,
      • within the fiberglass insulation,
      • at any vapor barrier already in the ceiling/roof
      • or on the underside of the roof sheathing.
  18. woodgeek

    woodgeek Minister of Fire

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    I'm no pro either. Can the manufacturer send you a drawing of the wall/ceiling interface?? Do you have any 'unfinished' locations you can inspect to try to figure out if the ceiling cavity is airsealed near that point??
  19. ScotO

    ScotO Guest

    I read that link and that's an interesting method.......if that was to be used, maybe Bret could consider installing a metal roof as well (which would further help out with getting rid of the ice dams).
  20. semipro

    semipro Minister of Fire

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    Which is exactly what I plan to do.
    I followed your insulation project Scotty and wished I could have done something similar.
    Unfortunately, I'm stuck in a situation where all the drywall (and plaster veneer) is already up and the roof structure is complex because of a mix of cathedral and non-cathedral type ceilings with some weird attic spaces.
    ScotO likes this.
  21. Bret Hart

    Bret Hart Member

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    Still reading through all of that info. Damn, that's a lot to take in but the pros know what they are doing.

    I had hoped to have a few more years left in that roof but after all of this, maybe it's time to move that up on the list. Option 3 looks good to me provided I can afford it.
  22. ScotO

    ScotO Guest

    That sounds like a great plan, keep me posted on your install. Down the road, I will be installing a metal roof. I'll definitely be considering insulating the sheathing when I go to do that roof......
  23. nate379

    nate379 Guest

    Well I had put a post but its gone now?

    Metal roof would help out.
  24. semipro

    semipro Minister of Fire

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    Actually, now that I look back at the PDF at that link what you'd really have would be what is shown as "Option 2" on page 71. This is where the roof is converted from vented to non-vented and the existing fiberglass insulation is used in combination with foam board installed above the existing sheathing to create a "cold roof".
  25. ihookem

    ihookem Minister of Fire

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    If you can get into an attic and see how it was insulated it will tell ya a bunch. Also, do you have much ice damming where there is no cathederal ceiling? I did notice with all the snow on the roof it takes little heat loss to make ice cicles. I had -9 and -4 here last week and there is no frost in the ground. That stuff insulates a lot. I don't get any ice cicles but I have energy heel trusses, closed off and sprayed with foam 4' up the bottom of the sheathing to not get ice. If you are getting ice where there is flat ceiling this is what I have done a few times to fix ice damming. I take 1" foam between the trusses. Keep foam 1" from the roof sheathing. This will make an air vent. Close off with foam between the top of wall and bottom of foam above the outside of the wall where the wall sheathing is. Foam doesn't have a dew point after 1" Make the foam go up between the trusses till ya get well above the insulation. I've done this before and it has worked. You may need more insulation and more venting to get the warm air out of the attic. I hope it wasn't confusing. By the way, my mom gre up in Utica.

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