Sliding doors are great for blurring the lines between indoor and outdoor. If you’re using a conventional track system that typically protrudes up to 1 inch from the finished floor, however, the amount you actually can blur is limited. Enter the lift/slide door with a flush-mount track.

A sophisticated piece of engineering from Europe, a lift/slide door operates on a simple concept: special hardware allows large and heavy door panels to be lifted (and slid) above a flush track while also allowing the door to be lowered onto seals that provide air and water protection. The beauty of the system is that you can have one material—tile, stone, concrete—running from inside the house to the outside for a seamless look. Seen in application, the setup is elegant in its simplicity and invisibility. It also hides how complex such a spec is to execute.

“Zero-threshold doors are very difficult to do right,” says Hans Berglund, of Edwards, Colo.–based Berglund Architects. “There are so many things to think about, including drainage, a tight seal, and other technical issues.” Berglund adds that there are other considerations that one would never think about with traditional doors such as snow loads and deflection. In one of his early lift/slide specs, the architect allowed the contractor to perform the installation, which didn’t go well. “We had to rip out the doors completely and basically start over from scratch,” he said. “The floor has to be dead flat and level for these systems to work properly.”

Though all components work together, a good track system is an part of a successful lift/slide installation. Oceanside, Calif.–based Weiland Sliding Doors and Windows—Berglund’s preferred brand—has developed a unit that takes the guesswork out of the system. “All lift/slide doors should have a drainage channel,” explains company CFO and principal Sue Weiland, which is why the manufacturer developed the Weiland Flush Track. “It has a gasket and weep system underneath.”

Typical sliding tracks protrude up to an inch above the finish floor while the Flush Track projects a mere 3/16 of an inch. The system also has built-in tubes that allow moisture and water to drain out and away from the house.

Warroad, Minn.–based Marvin Windows and Doors manufactures three types of tracks, including a recessed option with drainage. Pacific Architectural Millwork in Brea, Calif., also offers architects a variety of sills, and other companies have systems of their own.

But the track is only part of the story. To achieve maximum performance, you must keep movement to a bare minimum. “The system has a low tolerance for deflection in the header above the door,” Berglund says. “If you live in a place that gets snow loads or strong winds, you have to be very careful,” as the operation of the door might be compromised. “You could beef up the header to reduce deflection, but you pretty much have to use steel to avoid it.”

The freeze-thaw cycle also could affect the door’s performance. If proper steps aren’t taken, the constant movement could permanently damage the track, causing the drainage system to fail.

No matter how good manufacturers say their lift/slide systems are at sealing against air infiltration and moisture, common sense still applies. For example, Berglund uses a flush track only when a house has a significant overhang. “I try to have 5, 6, even 8 feet of overhang,” he says. If the overhang happens to be 2 feet or 3 feet, he uses the traditional sill with a 1-inch stop.

Local climate conditions also play a role, the architect says. If you live in a temperate climate such as San Diego, the flush track will work just fine. But if you live in a place with significant snow, wind, or rain, it will be more of an issue over time. Berglund produces detail shop drawings to convey to the installers what he’s trying to achieve, and he strongly recommends a waterproofing membrane installed from the inside out for added peace of mind. He concludes, “It’s well worth the money to have them installed by someone certified by the manufacturer.”