How to Replace a Patio Door

Sliding Glass Door Replacement

If you’ve been putting up with a drafty patio door that sticks, fogs up or leaks during a heavy rainstorm, it’s time to consider a new, energy-efficient replacement. While a high-quality door isn’t cheap, it’ll cut down on drafts, require almost no maintenance, and glide smoothly and latch securely. Best of all, you’ll save $300-plus if you install a sliding glass door replacement yourself.

At first glance, replacing such a big door may seem intimidating. But if you read through this article, you’ll see that installing a new sliding glass door is similar to replacing a window. We’ll walk you through each step of a sliding glass door replacement, including a special section on the critical flashing details that make the new door leakproof.

Manufacturers of higher-quality units have made installation fairly simple and straightforward. If you have experience installing a window or a swinging door, you should have no trouble with a sliding patio door. Other than basic carpentry tools, you’ll only need a 4-ft. level and a screw gun. But we also recommend using a reciprocating saw fitted with an 8-in. bimetal blade to hack through shims and nails (Photo 5). Unless you’re a brawny DIYer, another useful tool is a strong helper for short periods to assist with the heavy, awkward panels and door frames. In most cases, you can replace that old slider with a smoothly operating, energy-efficient new sliding glass door in about a day. Add a few more hours to re-trim the outside and the inside and you’re done.

Buying a Patio Door

Sliders are built from a variety of materials including aluminum, wood and vinyl. Low-maintenance selections include either vinyl or aluminum exterior cladding over wood core, solid vinyl and all-aluminum. If you want a slider that matches existing windows, consider buying the same brand. Check markings on existing window hardware to find out which brand you have.

Looking at the door from the outside, the operable panel determines whether it’s a right- or left-handed unit. Don’t be afraid to switch the way your original door opened if changing it makes access easier or furniture arrangements better. But be aware that heating vents work better in front of the stationary panel. They don’t stand up well to foot traffic. Plus, here’s how to repair a sliding door.

Measure the Opening Before You Buy

Measure the Rough Opening

Pry the interior trim free. Then chip away drywall to expose framing and measure the rough opening width (distance between studs) and height (floor to beam). Then select a new door that fits that rough opening. Before you run off to buy your slider, pull off the interior trim around the old door and measure the “rough opening” for width and height. (If you want to reuse the old trim on the new door, pull the nails through the unfinished side.) Make sure you measure to the framing right next to the old door jamb. You may have to cut away overhanging drywall to get at it (Photo 1). To check the height, make sure you’re measuring to the subfloor, that is, the wood or concrete that the doorsill actually rests on and not a secondary layer of particleboard or plywood (underlayment).You can check for underlayment by pulling off a nearby heat register and looking at the floor layers bordering the opening. Then select a new sliding glass door that fits your rough opening. The door catalog will list its rough opening requirements. The door dealer will walk you through sizing and door options. (See “Buying a Patio Door,” below.)

Once you get your door home, you’ll save a lot of time if you finish any exposed wood surfaces on the door before beginning the installation. That’ll save you from tricky brushwork cutting in around exterior claddings, weatherstripping and hardware, and keep smelly finishes out of your living quarters.

In our demonstration, we’re removing a 6-ft. slider surrounded by wood trim and vinyl siding. Our new sliding glass door was slightly smaller so we had to deal with a small gap surrounding the new exterior trim. Most new replacement doors will have a similar gap, no matter what exterior siding you have. If your old door has exterior trim fastened to the door frame, remove the trim and follow the installation steps we show. But if the siding comes right up to the doorframe (no trim), you’ll probably have to remove the siding or cut it back and restore it after installing the door in order to achieve a leak-free installation. And if you have stucco or brick, you’ll probably have to add trim to fill the gap and rely partly on high-quality caulk to seal out water. We’ll talk more about this later.

You never know how smoothly a patio door tear out and installation will go, so start in the morning to give yourself the best chance to finish up before nightfall. If you’re not going to beat the witching hour, cover the opening from the inside with sheets of plywood cut about 6 in. larger than the opening. Run 3-in. screws through the plywood and drywall into the framing where the holes will be covered by the interior trim. If it’s chilly out or threatens to rain, also staple plastic over the exterior to keep out drafts and water.

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