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TOPIC: Roofing over existing roof

5V metal roof

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With a currently installed 5V metal roof on a cabin in the mountains of North Carolina, my county inspector is questioning the installation suggesting that plywood sheets should have been used instead of the metal being attached to wood slats 16 inches on center which are attacted to the roof rafters that are 2x10 yellow pine which are 24 inches on center. Underneath, I have used 1/2"blue board"(foam vaper barrier) and then R36 insulation covered with plastic. Is this procedure an acceptable method?
Guest User

12/1/2003
I can't strongly enough suggest that one contact the manufacturer before creating assemblies and the same hold true here. Depending on the gage of the steel and the spacing on the battens you may be OK. The new codes call for a moisture barrier over the insulation unless the roof covering is tested otherwise. Check with the roof sheet manufactuer. If not you then need to check with the blue board manufacturer to see if it is apprved as an underlayment. My experiece is that it needs to have the joints glued. As well you for houses you need to supply a minimum 1" vented air space over the insulation. The horizontal strapping if more than 1" while providing the air space, it does not provide for vertical air movement. This then requires equal ridge an eves ventilation that van be achieved with vent mesh material. These code requirements are regardless of roof covering material. Hope this helps
Allan Reid
Dura-Loc Roofing Systems, Inc.

12/1/2003
I did leave out information on my question. We did install the 1.5" air spacers to the horizontal strapping before we installed the blue board. Also, the soffet will be vented with mesh screening. The 5V Crimp is 26 gauge and the horizontal strapping is 16 inches on center. The supplier has been no help in getting me the requirements for installation. The blue board was not glued. Am I dealing with a likely problem with strength of the roof or condensation?
Guest User

12/2/2003
Make sure the space is vented as much as possible and that the ridge vent provides slightly more ventilation than the eaves. I never asked what colour you put on as a dark roof will generally cause more dew point crossings than a white roof. If it condensates heavy it could drip an then come through the joints in the insulation. The worst time of of year is typically now where the air is actually extremely moist for the temperature and you get wild swings where the dew point is above freezing. When the weather turns really cold it typically goes away and only causes problems in unveted assemblies or if there is a lot of warm moist air leaking into the attic. In this case it can cause a minature ice dam under the roof. Keep a close eye on it and remember nobody goes up and looks at the underside of their asphalt shingles as it is on plywood. If they did they would see condensation as well. A roof breathes just like a a human and if done right it itis fine and healthy.
Allan Reid
Dura-Loc Roofing Systems, Inc.

12/4/2003
Is it best to have fasteners placed on the flat side of panel instead of the little ridge side of the panel. I was told if you put it on little ridge side of panel and slightly over torque the fastener you can bind up the panel off the decking. I had it put on the flat side of panel, a screw with a neoprene washer. Was this right . Joe F. with Total Construction San Antonio TX.
Guest User

12/15/2003
I would contact the manufacturer so that there is no warranty concerns and while you are talking to them ensure that the application is approved and to code. Having said that the 5V crimp is typically an agricultural or utility panel and not all manufacturers are approved for residential applications. The screw location depends on slope and sheet length. The sheets will expand with heat. Typically 3/4" over 80 degrees of temperature change. Fastening on the top of the rid allows the sheets to move more freely without affecting the seal. You should also make sure that you are using a quality screw for the application and that they are not overtightened. Basically there are more pressures on screws in the flat location.
Allan Reid
Dura-Loc Roofing Systems, Inc.

12/16/2003
Could you in general terms explain the differences between 5V and standing seam other than their appearance? What are the benefits for one vs. the other. Thank you
Guest User

1/18/2005
Mary, This requires a pretty lengthy explanation. Please email to me at [email protected] and remind me who you are ... I have a couple of helpful documents I will then send to you. Todd Miller
Guest User

1/19/2005