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Moisture Control for Old Metal Roof on Barn

1869farmhouse | Posted in General Questions on

My version of green in many cases is salvaging old structures and making them nice again.  It’s a balancing act sometimes.

This 2200 sq ft barn (approx 1940) is going to be living space.  The old metal roof is surprisingly water tight given the age and inattention, but it needs to be tight.  It will be covered in PV panels, so color and aesthetic is mostly moot.

I’ve seen silicone coatings, elastomeric coatings, aluminum with fiber paint, even petroleum (tar) coatings.  Having never done this, I was hoping someone had some insight.  Repairs will be difficult after PV install, so it needs to be at least a 10 year solution.

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  1. walta100 | | #1

    My opinion a new roof under solar panels is a good investment.

    If you do a spit and bubble gum repair on the old roof you will be removing and reinstalling the solar panels in a few short years to install the new roof.

    To my ear all the coating you mentioned seem likely to offer a taillight warranty when you can no longer see the contractor’s taillights the warranty is over.


    1. 1869farmhouse | | #2

      It’s very possible. The metal itself is pretty solid, certainly no holes or anything. From what I understand, these overlapping metal roofs can only leak in 2 ways. Through the screws/fasteners and via capillary action up under the overlap. The coatings real job is to stop this capillary action. I can seal the fasteners with new hardware and rubber washers no problem. The washers have about a 20 year life best case scenario, and likely less whenever these were added.

  2. GBA Editor
    Kiley Jacques | | #3

    Hi Austin,

    I appreciate your salvage-first mindset—it’s the greenest bet, for sure. Although this Q&A Spotlight post is about a metal roof on new construction, there might be a few things of interest to you in the section about moisture control—particularly if you end up replacing the existing roof with another metal roof: Does This Roof Need to Breathe?.

  3. gusfhb | | #4

    Pretty leak free in a barn is a hundred pots in a rainstorm in a house. Funny how perspectives change once you hang sheetrock

    what type of metal? Corrugated? Modern?

    Pics would hep advice

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