Does anyone know if this insulation installation is acceptable for a cathedral ceiling? The home is in the Pocono mtns. The layers from interior to exterior are as follows: 3/4" t&g pine- kraft faced fiberglass insulation ( possibly R30)- foam airflow spacer - 1" foamboard - roof sheathing - shingles. Won’t this constitute a dbl vapor barrier and cause problems?
The snowmelt has ben causing icedams and trouble. Thanks for any input!
Personally I am having hard time imaging a picture.
How did you see this?
Picture?
Illustration?
Anything more in info might bring answers.
Ditto
Main thing is whether or not there is airflow from outside air along the under side of the sheathing.
Here is one definition:
Ice dams are the accumulation of ice at the eaves and valleys of roofs, and in some winters create major problems. Insufficient attic insulation and/or attic ventilation can cause roof snow to melt and slide down to the eaves, where the roof surface is cooler and the melting snow freezes to the roof. Subsequent melting causes water to pool behind this dam and sometimes the water seeps between the shingle layers, wetting the roof deck and possibly the walls and ceilings below.
From what your are saying there are two vapor barriers the foam board and the draft face from the r-30 insulation. But i see the problem of the foam borad being against the roof sheeting being more of a problem because it defeats the air gap for the roofing material.
Were there problems with the shingles and how old were they. Are they showing signs of Heat and ventilation problems. Blistering, cracking, starting to shrink. And what type were the shingles. Aspahalt, fiberglass, Laminate or 3 tabs
Asphalt… No problems. This addition is only 8 mos. old. Ice dams are causing leaks. I agree… foamboard against the sheathing!!! it does have an air gap but its between the foamboard and the fiberglass batts. Thanks again.
The bottom line question…Should I advise them that the foamboard has to be removed?
Are you sure that is the case?
Early this winter and again lately the weather has been condusive to ice dam formation…freeze, thaw, freeze, thaw, repeat.
Yes. I have a clear view. There is no gap between the sheathing and the foamboard. The baffle is installed under the foamboard. The foamboard insulates the sheathing from the cold air gap… but it traps any moisture IN the sheathing… i think… Really confused why this was done.
Hi. Richard;
Pictures would be a plus, but let us see what we can do to help you here.
I am curious how you were able to determine the exact components and composition design of the roof.
Assumming that is what it is, I will go from there.
“How is it ventilated?”
Adequate ventilation is very important in a cathedral system, just as it is in a standard attic.
It takes a certain amount of space to fit in a ventilation system and adequate insulation into a cathedral ceiling. For example, in our area of the North East where R-30 ceilings are the norm for modern construction, any system with less than the equivalent of a 2X12 rafter depth has to be viewed with suspicion.
If the builder used fiberglass insulation, it takes 9 inch batts to give us the R-30 that we need.
We can see that a 2X10 rafter, which actually measures 91/4 inches, will not have adequate depth to provide a ventilation space. Of course, one of the main reasons for having ventilation in a roof system is to remove moisture so that excess condensation does not form on cold framing components.
In a standard gable attic there is a large amount of open air space between the finished ceiling and the roof sheathing.
It is possible to have adequate ventilation in this type of system with widely spaced soffit and roof vents because some circulation and mixing will occur in the open air area.
However, in a cathedral type system, each rafter bay must be viewed as a separate space to be vented.
Any moisture that migrates through the ceiling is immediately in contact with the rafters and sheathing.
By far, the best system is one that uses continuous ridge and soffit vents to vent each rafter bay.
foam airflow spacer - 1" foamboard
I am trying to visualize where the foam airflow spacer and the foam board are located.
I am assumming you mean Proper Vents stapled to the underside of the roof sheathing.
If that is the case, where is the 1" foam board located?
Several variables affect the installed R-value of foam insulation, including: the initial density of the foam; the blowing gas used (CFC, HCFC, CO2, air, or a number of other gases); how the foam insulation is handled (dents and chips adversely effect the R-value); the type of facing (if any) used; and the conditions in which the foam is installed.
Potential Moisture Problems
In cold weather, warm inside air containing water vapor can get past the wall finish and insulation and condense inside the colder wall cavity.
In hot-humid climates the same thing can happen, just in the reverse direction, humid outdoor air in the summer can condense inside cool/air conditioned wall cavities.
If enough of this happens, and the water cannot escape, wood rot, mold, and other moisture-related problems are likely to occur.
For this reason, building codes often require installing a vapor diffusion retarder on the warmest side of the wall cavity.
Foam board insulation is commonly placed between the exterior finish (i.e., siding, brick) and the studs of exterior walls.
To prevent air infiltration, you should place rigid insulation boards tightly together and seal the seams with tape or caulk.
However, this practice may worry some builders in cold climates since the foam board may act as a second vapor diffusion retarder.
Studies have shown, however, that condensation rarely occurs in these areas unless something else is seriously wrong with the wall assembly (i.e., massive uncontrolled air leakage into the walls from the house.)
If the assembly is constructed correctly, the inside surface of the foam board stays warm enough to keep water vapor in its gaseous state long enough for it to escape.
INSTALLATION & DESIGN CONSIDERATIONS
- Cathedral ceilings require vent openings at both eave and peak. See local code requirements.
- Standard batts require stapling facing flanges to framing.
- In cathedral ceilings R-30C and R-38C Thermal Batts are designed to friction-fit without stapling.
- Batts should be installed to provide minimum 1” ventilation passageway between the roof deck and insulation.
- When specifying kraft-faced or standard foil-faced insulation check local code requirements for limitations and install facing in substantial contact with finish material.
- Cathedral ceilings require an air barrier, such as gypsum board to control air leakage. Seal all penetrations to avoid condensation.
Well I hope there is enough information here to help, but there again, pictures would help.
Hope this helps a little.
Marcel :)
I would never tell someone to remove an item but refer it to a licensed roofing contractor for a possible ventilation problem. The double vapor can cause problems but not as bad as no air gap for the shingles.
I can see in the ceiling because there is a hole in the ceiling. I can reach up in the cavity. The builder nailed 1" foam board directly to the underside of the roof sheathing. Then he stapled foam dura vents to the underside of the foam board. Then he pushed Kraft faced fiberglass insulation into the cavity. He then installed T & G pine planking. My concern is that the dura vent isnt under the roof sheathing, its under the foam board. Why? The cold airflow isnt touching the sheathing where it is and the foam board wouldnt seem to increase the “R” value if there is a stream of cold air in the under (interior) side of it.
You may have three vapor retarders. If the baffles are used full height, there should be 2-inch spaces between each pair of baffles, so that they do not form a vapor retarder. I have seen a roof with baffles running full ehight, where the insulation was removed absolutely soaking wet. The right place for that foam board would have been under the joists, directly behind the wallboard, not directly under the sheathing.
It appears that the insulation (foam board) was installed in the wrong location (on the cold side of the air venting) to be effective as insulation to slow heat transfer.
I agree Larry, It is in my opinion that the location of the foam board might cause a dew point in that location.
There is nothing in the Building Science that I can find to support this type of installation.
The foam board should be installed in the interior space to supplement the R Values of the insulated assembly.
I would have strongly reccommended further evaluation of an Expert Insulation Contractor or a design Architect for this type of installation.
I have never seen this nor heard of this type of installation. 
Thanks very much. I’m really glad I belong To InterNACHI !!! I appeciate your help.
There are some good classes and diagrams here that will help you answer your question.
http://216.83.181.215/elearning/certainteed/resources/index.jsp
I agree Chris, I have taken everyone of those topics about 3 years ago and they are excellent. Took about 50 hours to go through all of them.
Good link.
Marcel :)