Strapping or No Strapping
June 12, 2009 | Filed under: Battens or No Battens, Misc, Roofing Answers, Roofing Installation
Question from June in New Hampshire:
Q: Greetings: – We are in the process of contacting contractors regarding the installation of a metal roof on our home and with each contractor that comes to the house we are getting more and more confused:
1. Should it be installed over the existing asphalt or strapping
2. Standing double locking seam- Does this tend to sweat on top of asphalt shingles?- one contractor states yes – the other recommends using it?
My response:
A: Thanks for investigating metal.
1) Some products CAN be installed on strapping. Very few MUST be installed on strapping. Most products CAN or MUST be installed on solid deck. If you currently lack attic ventilation and have difficulty achieving it then there is good reason to consider strapping but you must choose an appropriate product and you may wish to install vertical strapping followed by horizontal and then actively venting the resulting chamber.
2) A double lock panel should not pose any special issues in comparison to other styles.
I hope this helps some. If you have special circumstances that need to be considered please let me know.
Todd Miller has spent his entire career in the metal building products manufacturing industry. He is president of Isaiah Industries, an organization recognized as one of the world’s leading metal roofing manufacturers. Todd is currently Vice President of the MRA (Metal Roofing Association) and a Past Chair of MCA (Metal Construction Association). Through his website, he strives to raise the bar on standards and practices to provide property owners with the best possible products for successful roofing projects.
You may pull quotes from this article provided you include a link back to the original article on this site. You may not reprint this full article, or even a significant amount of the article, without explicit permission. To gain permission, click here.
I was told to use Foam type strapping instead of wood, what do you think
I’m going over the shingles with the steel panels over the strapping
Thanks in advance for your expertise
Thank you. I do not know what “foam type strapping” is referring to. Can you give me more details please?
Hi..
I’m planning on putting metal roof on top of an old roof that currently has shingles.. It’s just on a woodshed so there’s plenty of air flow.. the sheathing on top is roughcut pine under the old shingles.. Do I need to put up strapping or can I just put up metal?.. I like old rustic look so I’m not worried if it looks perfect but I was wondering if it would rot quicker without strapping.. Thanks!
Thanks. Good question. May I ask, is the woodshed “open air” … or is there some sort of heat or moisture source inside of it? I generally am in favor of not battens but I want to make sure we’re not creating a situation where you might end up with condensation inside the woodshed?
Hi Todd, we are looking at putting 26 gauge PBR on top of our 60×40 finished pole barn’s three-tab shingled roof in southern Michigan. The rafters are 24″ apart and the decking is OSB.
The pole barn is a finished, conditioned space with heat. We put R14 spray foam on the walls, R60 blown-in insulation in the attic and it’s well ventilated with a ridge vent and plenty of soffit baffles. Do you think there’s a need to run vertical and/or horizontal strapping? Should we add some kind of underlayment too like felt as a backup moisture preventative?
Thanks so much.
Thanks so much for your question and good description. I do not feel that strapping is necessary. It would help reduce summer heat gain of course but I do not feel it is necessary as far as condensation. Yes, according to building code, you should put down underlayment on top of the old shingles. I would suggest a premium quality synthetic or you could consider one of the reflective “Low e” type of underlayments. My company also sells an entangled mesh product called Dry Tech you can see at http://www.roofaquaguard.com This product would also create a thermal break to help with reduced summer heat gain and, to some degree, to help reduce winter ice dams. You may wish to check into it a bit.
Thank you so much for the quick reply and taking the time to answer! I am checking out the Dry Tech now. Looks like a smart product and Piqua is certainly close enough for a quick drive down if I needed (or am able) to buy a large qty in OH.
Just to confirm, we would put the premium quality synthetic or “Low e” type of underlayment against the shingles, and then the Dry Tech mesh goes on top of that, am I understanding that correctly? I tried to find installation instructions but struck out unfortunately.