Guest User
10/4/2007
I am considering installing a exposed fastner metal panel roof over an existing ashphalt shingle roof. The maufacturer recommends 1x4's installed on top of the existing roof and the metal attached to them. They also have a foil/bubble insulation they sell that can be laid on the roof prior to the installation. They claim great results as a raidiant barrier. Is there any where I can verify the claims? I dont want to spend time and money on something that doesnt work, or is only a 1% or 2% gain. The house is typical construction with an attic and bat insulation. It has vented soffits and I plan on replacing the turbine ventilators with a continous ridge vent system to vent both the attic and the air space under the metal. I plan on using some type of vented closure strip at the bottom of the panel and at the ridge trim detail. Then I plan on cutting open the existing plywood & shingle ridge to vent the attic thru the ridge vent. Thanks
Todd Miller
Isaiah Industries, Inc.
10/4/2007
You may want to go back to the manufacturer of the foil product for proof. Such radiant barriers are effective and probably worth the investment. However, improved ventilation like you mentioned is very beneficial too.
Guest User
10/4/2007
I am going to check with the manufacturer, but some research I found shows it may be more beneficial to apply it inside the attic over top of the existing insulation. Another question I have is regarding the use of an underlayment. My existing shingle roof is still in good shape with no leaks but is nearing the end of its life. The roofing manufacture says its ok to apply the purlins on top of the shingles and then attach the metal roof panels. I was wondering if there would be any benefit to also applying a layer of roofing felt. And if so would it be best under the purlins or on top? Thanks
Todd Miller
Isaiah Industries, Inc.
10/8/2007
I would install it over the old roof, beneath the purlins. I would also investigate using vertical purlins before horizontal ones. This will create an energy efficient ventable air chamber.
Guest User
10/9/2007
Thanks Todd, My plan is to do the vertical purlins on top of the truss and then the horizontal purlins on top of them. So it will form a 2' x 2' grid. I will probably add a small block 1' o.c. for the horizontal purlins for support and to make sure they are fastend 1' o.c. to the existing roof. I am sure ventilation will be great but I also think it will help with the panels laying flat and not showing thru and deviations in the existing roof. I still havent found any conclusive information on how much the radiant barrier will add. Do you know what manufacturers make a portable panel shear that will allow me to shear the panels on angle for the hips and valleys? I found one company (Dyna-Cut) but figure there must be others out there. Thanks
Todd Miller
Isaiah Industries, Inc.
10/20/2007
You may wish to try Swenson Shear
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