Ask Todd Miller *Metal Roofing Expert

Metal Over The Old Roof

Written by Todd Miller on August 4, 2009 | Filed under: Misc,Roofing Answers

A homeowner from Kentucky asked me:
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 alot 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 existing 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.

My response:
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. Avoding 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 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.

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About Todd

Todd's expertise comes from his years of experience in metal roofing manufacturing. As president of Isaiah Industries, based in Piqua Ohio, Todd runs a several of the world’s leading manufacturers of residential metal roofing; Classic Metal Roofing Systems, Kassel & Irons, and Green American Home. His personal goal is to educate homeowners of the long-life benefits of metal roofing.

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