Integrating indoor and outdoor spaces has never been more popular—or easier. Lift-slide and slide-fold door systems in large, multiple-panel configurations allow entire walls of glass to be opened, creating the ability to erase the boundary between interior and exterior living areas.

“I use them a lot between living spaces and screened porches to open the space, to create one large space in the summer,” says architect David Durrant of Durrant Design in Harvard, Mass. “So often windows and doors are barriers to views, especially when they're divided up by Colonial muntins.”

Several custom manufacturers—such as Weiland Sliding Doors, Duratherm Windows, Nana Wall Systems, Zeluck, Weather Shield, and Quantum Windows & Doors—will build lift-slide and slide-fold doors that can span openings up to 40 feet wide or more. “We actually did a home in North Dakota that opened up around 90 feet,” says Nana Wall president Ebrahim Nana, maker of the Nana Wall. “Architects keep pushing us to build bigger and more exotic openings,” adds Bob Hutchings, sales manager for Weiland, maker of Liftslide and Bifold doors.

Lift-slide doors resemble standard sliding patio doors, while slide-fold doors are hinged and look like French doors. Each has a distinct appearance and maneuvers differently, but both use European-designed hardware systems that allow them to operate easily in large, multipanel configurations. “The design of the hardware to make that huge door feel like a standard sliding door is critical,” says architect Daniel Martinez of Laguna Beach, Calif.

Lift-slide hardware separates the door's sliding and sealing/locking actions and allows even the largest sizes to operate smoothly. When the door is fully closed and locked, the weather stripping is compressed and engaged. Turning the handle on the main door panel both unlocks the door and lifts it off the weather stripping and onto a roller system. The weight of the door is supported by the top track.

Slide-fold doors can be configured to run on tracks installed at either the head or sill, depending on design preferences. Multiple door panels are joined with hinges and operate on sliding and folding hardware that swing the main panels inward or outward as a pair of French doors would. They then fold back onto the adjoining panels, which then slide and fold back farther in an accordion action.

Structural support is critical to long-term operation of these doors. In the design phase, the structure around the door opening must be properly engineered to support itself, says Jeff Williams, communications manager for Weather Shield, maker of the Weather Shield Telescoping Patio Door.

For instance, a header that sags over time will begin to restrict operation of the doors. The biggest challenge people have is making sure they've properly secured and engineered for the spans to hold up over time, says Keith Birden, vice president of Duratherm Window, maker of Sliding/Stacking and Lift/Roll doors.