How to insulate metal roof cabin

Mike McGreevy
7/11/2005
We bought a log cabin shell in West Virginia (Zone 6/7). The roof is a light green color gambrel style with a steep pitch. I've attached a photo of the roof system, which uses 2x4's on 24 inch centers. I'm thinking of using kraft faced insulated batts, with paper facing inward. T&G 1x6's will be used to face the ceiling. Any suggestions? Thanks very much for your help.
Allan Reid
Dura-Loc Roofing Systems, Inc.
7/12/2005
The building code calls for a roof assembly that has an interior air barrier, insulation, moisture barrier and roof covering as a minimum assembly and it must be ventilated. Your existing assembly includes the roof covering only. The moment you construct as described, you will have a hot air space and with any humidity loss etc, you will have condensation on the underside of the roofing which can drip. I would attempt to build the assembly from the outside in by attaching an underlayment to the top of the ceiling cords and the spray foaming the insulation, cover with a 10 mil plastic and your 1x6. Then remove the rdge cap and replace the closure strip with vented closure and check that there is adequate soffit ventilation.
KATHARINE C SHERIDAN
INSULATION
10/12/2005
I HAVE JUST PURCHASE AND WE ARE RENOVATING A BARN/CABIN WITH THE SAME ROOF SYSTEM 2X6 ON 24"INCH CENTERS, IT'S CORAGATED ALUMINUM ROOF WE NEED TO INSULATE IT BUT HAVE KNOW IDEA ON WHAT TO USE AND HOW TO DO IT.WE NEED IT EFFICENT AND NEED NO CONDENSATION.THE ONLY THING IS WE ARE PUTTING A CIELING SO WE CAN HAVE A ATTIC FOR OUR DUCTS FOR CENTRAL HEAT AND AIR. SHOULD I EVEN BOTHER INSULATING THE ROOF AND JUST DO THE CIELING OR WILL IT BE INEFFICENCT FOR THE CENTRAL AIR/HEAT PRODUCTION.
Allan Reid
Dura-Loc Roofing Systems, Inc.
10/13/2005
The picture sure helps. Wihout knowing your location but knowing you are going to heat and air condition, you are obviously in an area with dew point crossings. As you change the use of this building and introiduce more moisture, heat etc it will contribute to the condensation potential. Certainly installing ductwork in an attic is the worse thing one can do. There is no underlayment under the roof covering and it is on skip sheathing so you need to address this first. I would suggest installing all your roof penetrations first such as vents, chimneys and skylights and ensure they are weathertight. Then strap vertically with 1x2 along the rafters and install a thin sheeting to provide an air space and have the underside spray foamed in place. At the ridge instal a vented strip under the ridge cap to allow the air space to breathe. The foam provides both a moisture and air barrier. You can still run the ducts in the ceiling space however they do not need to be insulated as I would heat and cool this space. possibly you may want to vault the ceiling and leave the ducts exposed.
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