Q&A – Figuring out the best practices for metal roof installation

When it's as important as a roof over your head, conflicting information is the last thing you want. A homeowner installing a metal roof turned to our experts to get some clarification.

Charles, a homeowner in Salem, Oregon, was doing some reasearch on metal roofs and asked the following:

I am getting conflicting information on the following practices on metal roofs.

1. Underlayment. I read on different metal roof manufactures sites not to use Felt paper 15 lbs. or 30lbs. 15lbs felt will melt within 5 years under a metal roof. Synthetic underlayment is so much superior on many websites and Youtube.  Bruce & Dana  Metal Roofing Supplier of Salem Oregon  said that they recommend 30lbs felt paper. Of the half dozen Pole Barn builders in the Salem, Oregon area are telling me they install 15lbs or 30lbs felt paper underlayment.

2. On a screwed down metal roof; the screw's gaskets will rot within 15 to 20 years and have to be replaced. Again Bruce & Dana told me not to install a screwed down roof. They have had multipole contractors repair screwed down metal roofs I  don't want a major repair bill in 15-20 years and recommended a standing seam roof. Legacy Metal Works today told me that this isn't as big of an issue if you use 1-1/2" screws or #14 on a screwed down roof roofing.

Please give me your recommendations. HELP!!!

Our roofing expert Stan from Pacific West Roofing responded, saying:

1. I am not a fan of 15 or 30 lb. felt because they breath allowing air to get to the underside of the metal creating condensation which will become a problem for the plywood eventually. I suggest “high temp” peel and stick membranes because they won’t run, and they seal around the screws as well. Pole barn companies are usually building structures that are not enclosed or are not heated so they don’t see a need for sealing the underside of the metal. We do believe in it and it is security for us as installers for not only stopping moisture from moving upward beyond the plywood, it also stops any leaks through the top of the metal downward as well.

2. I believe they are speaking of exposed fastener roof systems, not concealed screws such as Easy Lock from Taylor Metal. This is where the edges that snap over the previously mechanically fastening panel, covering the screws. There are zero exposed fasteners especially if you use a hook eve of hook locking eve and you won’t need screws. Exposed screwed down or nailed down metal roofs are not a good idea in our climate. The fastener grommet will get destroyed by UV thermal cycling and water exposure and both will dry out the rubber grommet.

I hope this helps!

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