Water is the bane of a builder’s existence—and its profitability. Despite what you think are your best efforts, it seems to find a way into a window, roof, wall cavity, or door opening. Sometimes, the problem is obvious right away. Other times it hides under the surface, rotting away the structural and/or insulating integrity of the house, leaving mold in its wake. Either way, the fix is likely to be extensive and require removal and replacement of several finishes, inside and out, to get it right.

Patio and deck doorsills are especially problematic. Often at grade and exposed to the elements, they are on the front lines of where water settles after a rainstorm or snow melt. Improperly built, the sill becomes a conduit for incidental water to migrate into the house and under the finished floor with potentially catastrophic results. “It’s a high-risk location, especially when it’s on the same plane as the outside,” says Alan Mooney, president of Criterium Engineers, a Portland, Maine, construction consulting firm. Most prehung door assemblies do a good job of sealing the door to the sill, he says, but installers sometimes fail to properly build the sill-to-floor assembly to create an effective water barrier.

Learn more about markets featured in this article: Portland, ME.