Metal Over The Old Roof
August 4, 2009 | Filed under: Misc, Roofing Answers, Roofing Installation
Q: I currently have 2 layers of shingles on my house. I live in south western KY and the house is subjected to lots of thunderstorm with high winds, hail, and heavy rains. We also have several tornadoes. My roof has a lot of wind lift from the last storms that went through and now I have had leaking into the house.
Would it be better for us to install a metal roof over our old roof?
If so, I have a few questions about metal roofing. Since we live in the very HUMID southern US, do we need the felt on top of the existing shingles? Are vents recommended being installed on the ends? What is the standard for installation…typically do you screw the metal directly into the the decking or do you use a spacer between?
I KNOW nothing about metal roofing and I really need some help so that I won’t be informed wrong by the contractor.
A: Metal is a very low weight roofing option — typically from 1/3 to 1/8 the weight of conventional shingles. This allows it to frequently be installed over existing shingles, even multiple layers. Building codes sometimes dictate no more than two layers of roofing but often building inspectors will waive the requirement for a low weight metal roof. Avoiding landfill disposal of the old roofing is a very green way to go!
I do always suggest a new layer of underlayment over the old roof shingles.
As far as ventilation — attic ventilation is a great way to increase the health and energy efficiency of your home. It helps avoid the buildup of heat and moisture. Most metal roofs fit very well with ridge or other vents.
Most metal panels, if installed over solid decking or existing roofing, do not require additional spacers.
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.
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Hope you can help. I have searched diligently on the internet and can find nothing about a metal roof being installed over an existing Arizona Flat roof. I have a house about a half mile away that appears to have had this done. Just wondering is it a possibility and any extra costs or even less cost for the project. Any help or suggestions will be appreciated.
Thanks,
MSgt Harris (U.S. Air Force – Retired)
Thanks for your note and, most importantly, thank you for your service to our country. With photos of the project, I’d be able to relate more exactly to what’s been done but, yes, there are metal roofs appropriate for low slope roofs. While virtually all metal roofs can be installed down to a 3:12 pitch (the minimum pitch required for asphalt shingles), standing seam roofs can be installed usually down to 2:12 and mechanically standing seam roofs can be installed in some cases on pitches as low as 1/4:12. Feel free to email photos of the project to me at todd@asktoddmiller.com