Cathedral Cieling.....


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Old 03-02-13, 07:58 PM
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Cathedral Cieling.....

Hello all, I would like to liven up my living room by adding a cathedral or vaulted cieling. I have not yet been into the attic, to verify if it is a rafter or truss roof, as I have not moved in yet, however I would like to get an idea of what costs are involved on the engineering end. I am not to concerned about the construction costs as there are "retired" contractors in the family, however the engineering I am unfamiliar with. Any info would be appreciated. Thank you
 
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Old 03-03-13, 05:38 AM
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It will depend on what you find you have for the existing rafters / trusses. If adequate space for insulation does not exist you may have to add what's called scissor trusses.

Also there needs to be space between the insulation and the underside of the roof sheathing along with vents in the soffit and peak of the roof for adequate ventilation for moisture control.

Do some research as well on vapor barriers for this type of ceiling. If not done right for your specific climate zone, you can end up with a rotted roof.

Insulation, ventilation and vapor barrier. Those are your key elements that must be worked out for your location.
 
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Old 03-03-13, 04:15 PM
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I'm glad you're not concerned about the costs, this is not a small project.
 
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Old 03-04-13, 07:41 PM
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Thanks all, the reason I mentioned that there was not too much of a cost concern, is because there will be no labor costs. Most of the family is involved in construction in one form or another, however I feel an engineers design will speed up the process, and satisfy the permits. This is only being done to one room, and it is only one slop of the roof. I had a chance to go into the attic, and the roof is a rafter and cross tie design. There a few A/C ducts that run across a small portion of the room, as well as few runs of wiring. It appears to be a good candidate for it, however I have an untrained eye.
 
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Old 03-04-13, 08:14 PM
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The last house I did this to needed to have the entire 1/2 of the roof (and ceiling) ripped off all the way to the ridge and central load bearing wall. The ridge was replaced with an LVL, and the rafters were replaced with 2x12's. The ceiling remained at the original 9 ft height for the first 7 ft or so then the ceiling joists were headed off into an LVL. Above this LVL, the wall was plumb up to the new rafters. The load path of the ceiling LVL needed to be extended from the 1st story to the basement floor. The ridge LVL was kicked down to the load bearing wall below and to the ceiling LVL. This was all drawn by an architect, approved by an engineer.

If I were to do it again, I'd probably want to use TGI's instead of Hem-Fir for the added thickness and strength. But 2x12 Hem-Fir was what they spec'd.

Not sure what the going rate is in your area, but depending on how involved you want them to be in the process, I would think you could expect to pay anywhere between $5K-8K for a drawing and basic services.
 
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Old 03-04-13, 08:27 PM
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I know this has been gone through a number of times, but what is the preferred method to insulate cathedral ceilings?

-I have read to instead fiberglass batt with an air gap behind to allow for moisture ventilation

-I have also read to densely pack cellulose or spraying insulation to eliminate airflow, and prevent it from carrying moisture

Any opinions?
 
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Old 03-04-13, 08:37 PM
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Spray insulation !!! it the way to go!
Seen it with great results
 
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Old 03-05-13, 09:55 PM
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If you're going to use the same framing members as roof rafters and ceiling joists, I would add 2" of rigid foam insulation to the underside of each rafter/joist to defeat thermal bridging and to create a deeper bay. I would insulate the bays with mineral wool batts, leaving 2" behind the batts for airflow. Apply 6 mil. poly over the space as a vapor barrier before installing and air sealing the drywall.

The roof will need continuous soffit vents and a ridge vent to keep the insulation dry and effective.

A sealed "hot roof" is probably not a great idea with a cathedral ceiling, nor in the NJ climate.
 
 

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