No matter what type of metal roof you have, all leaks come from seams, gaps and holes in the roof system. Finding the exact point of entry is often difficult but once you have identified the cause, you are confronted with multiple product options and techniques.
Why Seal Laps?
Most metal roof seams are internally sealed with a 1/8″ thick strip of double sided butyl tape. While this may sound good in concept, we have to assume the tape has been laid without gaps along the entire length. Even if this has been done correctly, there is no guarantee that the tape is fully adhered on both sides once the laps are secured. On R-Panel roofs, the butyl tape can sometimes be twisted out of position by the self drilling fastener used to secure the roof.
Even Standing Seam metal roofs that do not have leak causing fasteners over the ribs still uses screws at end laps. At least 3 screws are visible along the deck and 2 along the ribs (left). Troublesome leaks forced the building owner to seal end laps with a asphalt mastic. This is a cheap, short term fix and something you should never consider. Also pay attention to gaps and fish mouths.
Seam Tapes
Your quickest fix in a pinch. If you only have a few hours before rain is expected, this is your best option. The SeamStitch® Butyl Tape and Eternabond® Webseal both have fabric backings that make it compatible with roof coatings. When installing seam tapes, use a metal roller to activate the dry adhesive. Tapping down with your fingers is not enough. Pay attention to gaps1 and fish mouths2. When going over screw heads, do not slit the tape3. Use a small hammer and tap over the screw head, then cut a hole the size of the hex head. The tape should still adhere around the washer. Overlap more than 3″ at ends to prevent folds4.
If weather and time permits, roofing fabric and bonding adhesive is a better method in my opinion. Seam tapes have greater initial adhesion and work best if used over clean and bare roof substrates. Liquid adhesives seem to work better over previously coated or granulated surfaces.
Fabric Tapes and Bonding Adhesive
Fabric tapes such as SeamStitch® Polyester Fabric are installed by applying a thin coat of bonding adhesive over the seam then rolling out 4″ or 6″ wide fabric immediately while the adhesive is still wet. Use a small roller to keep the fabric flat on the roof. Finally, apply another coat of the bonding adhesive over the fabric to saturate it completely.
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