installation over 2X6 TG deck

Guest User
1/18/2018
Hello, I would appreciate your help with an unusual situation. I am replacing a wood shake roof with a metal roof. The current roof structure consists of the following. Hip roofs, "cathedral" ceilings. The house consists of 4 individual cubes of varying heights, attached to each other. Each cube has its own hip roof. Total roof area is 50 squares. The ceilings are exposed (visible) 2 X 6 tongue and groove deck above exposed beams, also visible from the interior, spaced 48 inches apart. Above the 2 X 6 TG deck there are 2 inches of poly iso insulation. Sleepers are nailed through the insulation and the wood shakes are nailed to the sleepers with the appropriate membranes in place. THERE IS NO PLYWOOD DECKING ABOVE THE INSULATION. The entire roof envelope is about 4" thick. I am planning to maintain the 4" thickness because the roof has eaves extending 4' feet (yes that is 4 feet) beyond the outside walls. A thick roof will look terrible and I am already getting good insulation. This is my question? Can I install a standing seam metal roof the same way the current roof is installed? Can the metal roof go on sleepers or does it need a plywood deck on top of the poly iso insulation. I plan to replace any damaged sections of insulation or the whole thing if it is not sound. Will the metal roof provide better or worse insulation than the wood shake roof? Thanks for your advise. Paul
Todd Miller
Isaiah Industries, Inc.
1/18/2018
Technically, there are metal roofs that could probably be installed over what you have. That said, someone would have to take a look at the spacing of the "sleepers" and the product you're installing to ensure it meets Florida Building Code. However, i want to caution you ... your wood shakes naturally "breathe" much more than most metal roofs, meaning that vapor and moisture from inside the structures can escape out. My concern is that when it is cool in the evenings and there is warm moist air trying to get out, it will condense on the back side of the metal panels. I think that decking would be very helpful to avoid that but more than that may be required as well, such as decking with an air space on top of it that would allow the vapor to be vented out. There are also aluminum and steel shake roofs available which, in this case, would offer you a special benefit. The metal shakes have a formed thickness and an integral air gap rather than rest right on the roof deck. That would prevent them from dropping the temperature of the roof deck as much, further helping to avoid the possibility of condensation.
Eric Novotny
An informed customer is the Best Customer!
1/18/2018
What type of foam is the 2" foam and any facers on it? Shouldn't be any risk from conditioned room side moisture here with the 2" foam. Some underlayment over the foam and maybe some cross battens to allow for a vent space might be order. Definitely need to check code as Todd mentioned.

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