Rubber roofing membrane has been commonly used on historical homes and buildings in attempts to water proof leaking box gutters. Some years ago this may have been the best box gutter repair option available. However new developments in the roofing industry have lead to better way to seam membranes, better flashing accessories, and easy to install metal trims that not only protect the decorative cornice work but accent and enhance the look.
Here’s a look at why lining a box gutter with rubber roofing is outdated
Rubber roofing box gutter liners Rely on Glue
The number one reason that rubber box gutter liners fail is because the seams are made with glues and adhesive and they deteriorate in ponding water. Box gutters are notorious for holding at least some rain water and they hold most of the snow and ice over the winter months. The glue holding the rubber liner together quickly deteriorates because it’s not designed to function in standing water.
Instead Try a membrane the seams by hot air welds instead of glues and caulking. PVC membranes are a great option for box gutter because the seams function in standing water and don't rely on glue.
Rubber box gutter liners don't have drain flashings.
When rubber roofing material is used on a commercial roofing project with roof drains, the rubber is secured to the drain by a clamping ring. But there’s no commercial roofing drain assemble in box gutters, and therefore no way to secure the rubber roofing around the downspout hole. The rubber roof liner is cut around the drain and glued down as best as possible but there is no seal to stop water from backing up and traveling under the rubber membrane further damaging the other seams. The more glue, caulking, or flashing tape that is used in attempts to water proof the outlet hole only restricts water flow that much more and causes more water to pond which further deteriorates the seams. It’s a no win situation.
Instead Get Custom drain flashing that will fit inside of the downspout. This flashing will prevent water from running back underneath the box gutter liner and causing leaks. The drain flashing will also be hot air welded.
Rubber box gutter liners don't have metal edge trim
When rubber roofing is used to line a box gutter it is brought over the edge of the box gutter and terminated with aluminum termination bar and screws. Not only does this affect the look and curb appeal of the decorative trim, it allows excess water to spill over the edge of the box gutter and run down the face of the trims causing rotting, peeling paint, and / or staining.
Instead use a 2 pc compression metal edge trim. Not only does it protect the box gutter trims, it adds to the look of the home or building.
PVC membranes are a great alternative to rubber box gutter liners because it has hot air seams, custom drain flashing, and decorative metal edge trim in colors to match your home or building.