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-   -   not venting a metal roof (http://www.diychatroom.com/f9/not-venting-metal-roof-12367/)

penny0322 10-14-2007 11:26 AM

not venting a metal roof
 
My log cabin roofer has installed a standing seam metal roof and he told me he does not need to vent. The roof has a 12-12 pitch and is a cathedral ceiling. This is how my roof is installed. First and starting at the top is the standing seam metal roof light in color, below is one sided bubble foil with the foil facing the metal roof. Below the bubble foil is 16" on center perlins (2 by 4"s) ,attached to, 2 by 12 I joists. In between the I Joists is a fiberglass, R-30 insulation(faced).Attached to the bottom of the I joists is another layer of one sided bubble foil, with the foil facing the drywall. last, of course is the drywall. Will this really work or am I going to end up with a ton of moisture and a rotting roof? Please can some one help me with this. I am getting ready to have the drywall installed and I am afraid of this roof!

Audiofn 10-17-2007 08:58 AM

I think I understand what you are talking about. You do not have to vent a metal roof. It is still a good idea but not required. I did a HUGE amount of research on this topic before I decided to put venting on the roof that I am doing for my home. My home is a little different however in that I used super insulated panels. The SIPS construction has shown some issues with moisture escaping out the seams between the panels. This is not so relevent with a stick built house like you have. He seems to have the foil facing the correct way and acting as a vapor barrier. The bubble wrap should take up any air gaps under the roof so this should prevent moisture from building up in any air gaps under the roof because there should not be any. I am not sure about using the foil as a underlayment. As long as it is rated for that I think you are fine. Do the panels lay flat with this set up? Seems that the foil would make them buckle.

the roofing god 10-17-2007 10:26 PM

you should be fine,I believe that`s what`s referred to as a cool roof application

Ed the Roofer 10-18-2007 10:49 AM

The way your metal roof is installed put the building envelope below the metal roofing system, so there should be no condensation problems on the underside of the metal panels.

Ed

joasis 10-18-2007 01:05 PM

There is nothing wrong with the installation. matter of fact, in Oklahoma, I doubt w would have placed the second layer of "double bubble" or solar guard, as it wouldn't be really necessary.

maestro 03-25-2011 04:28 PM

Maestro
 
The roofing retrofit mentioned in "not venting a metal roof" is very similar to the roofing project I had done August, 2010. Here is my project, starting from the top (like the penny0322 project):
My house is a Lindal Cedar Home built in 1973.
It is chalet, open inside with a loft, and large windows. We heat with a wood stove.
My roof is also a 12/12 pitch, and a cathedral ceiling.
At the top: 26 gauge pole barn type metal roofing (dark brown),
Next, one side foil bubble wrap with the foil on the upper side (facing the metal roofing.
The roof is framed with 2X8's. The metal roofing is screwed to the 2X8's over top the foil bubble wrap. The 2X8's are filled with fiberglass insulation (R-30). [We realize we are not getting R-30 performance because the insulation does not have enough space.]
This framing is fastened to the existing roof with wooden blocks and lag bolts.
The existing roof is a 2" thick tongue and grooved Ponderosa pine ceiling deck with 1" of compressed styrofoam insulation. The styrofoam insulation was saved by the contractor. The 2" thick Ponderosa pine is also the ceiling of the house.
So, to conclude, here is my roof starting this time from the bottom:

2" tongue and grooved hardwood pine supported by 4X10 beams.
1" styrofoam insulation.
8" fiberglass insulation inside framed 2X8's.
foil bubble wrap (with the foil facing up).
26 gauge pole barn roofing.
The roof does have a ridge vent, and pole barn roofing has ventilation channels.

The roof does not seem to have any moisture problems. We had 60 mile an hour winds this winter with no problems. The house is much easier to heat and cool.
I welcome any comments.

seeyou 03-25-2011 06:39 PM

I welcome any comments.

Start a new thread. You'll get better results.


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