Note that sliders can have different types of tracks, so it’s important to get the right type. One, which is most popular in the Southwest, is nearly flush with the finish floor. It does a good job at dust and air control, but no one boasts of its ability to stop windblown water.
FRAMING IS CRITICAL If you take away just one piece of information from this article, make it this: In a long-span door installation, the quality of the framing is absolutely critical. The top track of a bifold or the bottom track of a sliding system must be level to within 1/8 inch per 12 feet of length, and it has to stay that way for the life of the door. Adair says that while it probably won’t take any unusual framing to get this stiffness on a 12-foot opening in an existing wall, wider openings must be engineered. That makes them more appropriate for an addition or new home. “It’s unlikely that someone would put an 8- or 24-foot-wide system into a retrofit,” he says.
“People who have been in business for a long time understand that plumb and level is important,” Stevenson says. “The difference with these systems is that the opening has to stay that way over time.” Top-hung systems are more sensitive to frame movement. In a slider, the panel extends halfway into a 1½-inch-deep track, leaving ¾ inch of play. He says that there isn’t such play in a bifold, and that it can start to bind after ¼ inch of sag.
Door manufacturers say that an LVL beam should be fine for a 12-foot opening, but for longer spans they recommend a steel I-beam with a wood buck attached to the bottom flange. “We seldom see built-up beams,” says Jon Sawatzky, an architectural consultant with Loewen. “Many engineers have concerns because of deflection and warpage with SPF lumber.” In a sliding system with a 10- or 12-inch-wide track, some contractors install two headers side by side. In this case, manufacturers recommend spanning the width with 1-inch plywood. It adds rigidity, and provides a continuous, solid anchor for screws.
Some contractors will set the header higher than necessary, and place shims between it and the door system’s upper track. That way, the shims can be adjusted if there is settling. For minor settling, most door systems have adjustments built into framework so you can re-square or re-shim. “Our [sliding] doors have shims that you can adjust with a screwdriver from inside the home,” says Kolbe & Kolbe Millwork’s product manager Lance Premeau.
To avoid problems in a new home or addition, experienced installers warn against installing the door system before the roof and drywall are in place. Chris Brown of Exclusive Windows and Doors in Austin, Texas, has installed 20 of these systems, in openings as long as 24 feet. The only callback he has ever had was for a sliding system on the bottom of a three-story home. “It was working perfectly when we installed it, but as the workers loaded up the house it settled, and it started to pinch the door panels between the top and bottom of the frame. We had to uninstall the top jamb, then re-shim and re-install it.”
INSTALLATION ISSUES As for the door system itself, some dealers have certified installers, some don’t. Most manufacturers insist that an experienced contractor and a helper should have no problem installing either type of system in a day the first time they do it, if they follow the manufacturer’s instructions and take advantage of the manufacturer’s technical support, where available. With folding doors, the installer preassembles the frame, then slides it into the rough opening, shimming where necessary to get the top track plumb and level. With a sliding system, the installer assembles the track pieces in place in the opening. Once they have a few installations under their belts, they should be able to complete one in about four hours.
Brown has had no quality problems with any of the doors his company has installed. “These units are so well engineered and the hardware works so effectively that, if installed properly, you don’t have any problems,” Brown says. “But some of the details have to be right on the money,” for example, making sure that everything is installed square and level. Another is making sure that the installer follows the fastening schedule. “The folding door system hangs from the top rail and is subjected to a lot of torque when the doors are opened,” Brown says. “It has to be secured rock-solid.”
In other words, the same can be said for installing these doors as for framing the opening they will go into. It doesn’t require any new skills on the part of the contractor, but it may take more care than they are used to exercising.
—Charlie Wardell is a freelance writer in Vineyard Haven, Mass.