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Old 06-10-2008, 03:20 PM   #1
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inulation above cathedral ceiling


I have a bedroom with a cathedral ceiling which is improperly insulated and I hope to correct. Rather than a “true” cathedral ceiling, the ceiling is sloped to a lesser degree than the roof pitch, in a matter similar to scissor trusses (except they really aren’t trusses, but I hope this is clear). I’ve attached a pic.

I was originally thinking that I could craw in this area and fit fiberglass batts between the ceiling joists. As I think about this, I now doubt that I will have enough room in which to work, and am starting to question the safety of this idea (I don’t like the idea of sliding down into the eaves and getting stuck). I suspect that my options might be limited to the removal of the drywall ceiling or of the roof deck. I thought I would see if anyone had any other thoughts though.
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Old 06-10-2008, 03:57 PM   #2
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inulation above cathedral ceiling


Lanterdan
are the existing rafters 2x6 or 2x8 ? I would suggest removing the drywall from the bottom of the existing roof rafters and furring the bottom of the rafters at least 2". I would rip down some 2x material and glue and tack them to the bottom of the existing rafters. once all in place get some 3-1/2" deck screws and screw them every 16" apart. then install baffles to the bottom of the roof deck, from the attic area to the eves. Then install what ever insulation would fit with out compressing the insulation tight.
if you want to use wider material you will have to drill some 3/8" countersink holes and a longer #2 square drive bit for the deck screws. as far as glue I use PL Premium

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Old 06-10-2008, 04:19 PM   #3
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inulation above cathedral ceiling


The ceiling joists are 2x6 (as are roof rafters). Mybe I'm missing something, but I don't see the point in furring out the joists. Is there harm in having the insulation stick past the top of the joists, as long as there is still room for ventialtion above?

The roof, is probably a few years away from replacement (although it certainly could last a few years more) which is the only reaon I suggested going in that way.

To further complicate matters, the joist spacing is uneven, so if I went with fiberglass batts I would have to cut each one to the proper width which wastes time and material. I'm wondering about putting some sort of net over top and blowing in celluse. But I have a tendacy to stick with what I know and that would be fiberglass.
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Old 06-10-2008, 04:42 PM   #4
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inulation above cathedral ceiling


I would give some serious thought to blown in insulation, unless I am missing something - but that is just me.

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Old 06-10-2008, 05:37 PM   #5
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inulation above cathedral ceiling


The problem with blown in inulation as I see it, and perhaps someone here can help, is since the ceiling is sloped I'll need to attach some sort of netting over the top of the joists to hold it in place (I think), as while as install baffles near the roof eaves. Which leads back the orginal question, is there a way to do this without removing the drywall ceiling or the roof deck?
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Old 06-10-2008, 05:43 PM   #6
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inulation above cathedral ceiling


It was always my understanding that if you put , for argument sakes an R-30 insulation into a 2x4 joist you will not achieve the full R value. Because air will flow through the insulation sides thus defeating the full R-value. this is something that I always considered when insulating,
Somebody correct me if I'm wrong.
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Old 06-11-2008, 08:48 AM   #7
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inulation above cathedral ceiling


Can you remove the soffit and install baffles from there? Then blow in cellulose.
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Old 06-11-2008, 11:44 AM   #8
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inulation above cathedral ceiling


Its a no overhang roof, so I'm afraid that can't be done.

There area currently R-13 fiberglass bats run perpendicular to the ceiling joists (w/ the cavities below them empty), so I think I'm going to need to remove those. I suspect there isn't going to be an easy way to do this.
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Old 06-11-2008, 12:17 PM   #9
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inulation above cathedral ceiling


Where are the air intake and exhaust points for the venting?
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Old 06-11-2008, 12:28 PM   #10
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inulation above cathedral ceiling


gable end vents
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Old 06-11-2008, 01:10 PM   #11
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inulation above cathedral ceiling


So you have only two gable end vents and no soffit intakes?
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Old 06-11-2008, 02:10 PM   #12
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inulation above cathedral ceiling


Correct.
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Old 06-11-2008, 02:57 PM   #13
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inulation above cathedral ceiling


Not an expert, but with no overhang and no fresh air intakes over the soffets, you do not need an air baffle. The purpose of the baffle is to allow cold air on the underside of the roof from the soffet intake. Again, not a pro, based on your first picture, I don't believe you have enough cold air flow over the insulation.
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Old 06-11-2008, 03:42 PM   #14
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inulation above cathedral ceiling


Quote:
Originally Posted by 47_47 View Post
Not an expert, but with no overhang and no fresh air intakes over the soffets, you do not need an air baffle. The purpose of the baffle is to allow cold air on the underside of the roof from the soffet intake. Again, not a pro, based on your first picture, I don't believe you have enough cold air flow over the insulation.

Correct. If you don't have soffit vents, there's no need to put in baffles. Their purpose is to keep an open path from the vent to the attic. Since you don't have the vent, no need for the baffle.

My suggestion is to blow in loose fill cellulose. Lowe's and Home Depot usually will rent (loan) you a blowing machine if you buy enough insulation. Blow to the bottom first and fill upwards. It will work fine.

If you have any combustion appliances venting through this attic, use a piece of flashing to make a ring around the flue(s)out two or three inches out and the same higher than the insulation to keep it away. Cellulose has been treated with fire retardent, but it is just chewed up newspaper after all. Better safe than sorry.

I don't know what part of the country you live in, but around here (midwest) we like to see an R-38. You can re-use the fiberglass that's up there, but run it between the ceiling joists. Also, make sure the paper is to the warm side. i.e., hot climates...paper toward attic; cold climates...paper towards ceiling. Make sure if you decide to re-use it, when it is installed that it touches the drywall as much as possible. The effectiveness drops dramatically when contact is not made. Also, try not to compress the fiberglass as this also reduces r-value.
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Old 06-11-2008, 03:57 PM   #15
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inulation above cathedral ceiling


I was under the impression that I had to maintain a minimum of a 1" airspace between the top of the insulation and the roof deck. I'm not sure how to do that if I just blow insulation down into the eave area, which is why I thought baffles might still be useful. Can I just blow celluse in sloped areas like this? I'm worried that it will all migrate down hill, unless I where to fasten some sort of netting over top. I still have the problem of removing the old fiberglass which I don't have access too.

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