How to Replace a Patio Door

Measure the opening before you buy

For Walker, the lead-up to ordering the door is the most sensitive part of the whole project. Take your time and double-check your figures to save massive headaches down the road. Pros know to take as many measurements as needed and always to check their work. Even then, you may feel unease when it’s time to place an order. “There is always that feeling in the back of your mind,” says Walker, “that makes you wonder if you have the dimensions perfectly measured and locked in.”

• Pry free the interior trim.
  • Chip away drywall to expose framing (if needed).
• Measure the rough opening width (distance between studs) and height (sub-floor to header).
  • Make sure you measure to the framing, not simply the old door jamb. You may have to cut away overhanging drywall to get at it.
  • To check the height, make sure you’re measuring to the subfloor.
  • Measure to the wood or concrete that the door sill actually rests on and not a secondary layer of particleboard or plywood (underlayment).
  • If needed, pull up a floor vent to look at the flooring layer’s thickness.
• When you order your new door, select one that’s slightly smaller than your rough opening.
  • It’s much easier to install a door slightly smaller than the rough opening rather than one slightly larger.
• Rehang any trim you removed. (Optional.)

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Re-measure the new door

• Once you receive or pick up the new door, verify all measurements before tearing out the old door.
• Re-measure the rough opening.
• Measure the new door.
  • I’ve seen the wrong-size door delivered to job sites in the past. You definitely want to check this before you do any demolition work.

Remove old sliding glass door from frame

This is where the job really begins. One quick note: although many of these photos show a single worker, Walker suggests finding a helper to tackle this project. As he says, “From holding things to checking level and plumb calculations, having a second set of eyes and hands is important on a job like this to get things right and make it easier.”

• Latch the door to secure it temporarily.
• Unscrew and remove the inside head stop.
• Unlatch the door, tip the top of the sliding panel inward and lift it off the track.

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Remove angle brackets

• Unscrew and remove any angle brackets at the top and bottom of the stationary panel.
• “In some cases,” says Brandon Walker, “angle brackets may be connected to other components or hardware on the door, such as rollers or tracks. Before removing the brackets, disconnect any attached components to ensure a safe and easy removal.”

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Remove the stationary panel

• Pull the stationary panel away from the side of the frame, slitting any caulk or paint with a utility knife.
• Tip it inward and lift it out of the frame.

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Remove the old sliding door frame

• Pry off the exterior trim.
  • If you’ll be reusing it, set it aside somewhere it won’t be damaged.
• Use a reciprocating saw with a longer bi-metal blade to cut between the framing and the door jamb.
  • You’ll typically be cutting through a mixture of nails or screws, insulation, and shims.
  • Go slow, and let the saw do the work.
• With the head and side jambs cut free, tip the frame to the outside.
• The frame will likely be glued to the floor with beads of sealant, and it may take substantial prying to free it.

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Apply flexible leakproof flashing

Flexible flashing comes in 4 to 6 inch wide rolls and adheres to underlying surfaces. It’s imperative that the flashing laps over any deck flashing or weather barrier below the door.

• Apply flexible flashing directly under the door sill and two inches up the sides.
• Begin applying flashing at the bottom and work your way up.
• Don’t peel the backing off all at once – it’s too easy for the flashing to stick to itself.
  • Peel back one end of the flashing, secure it, and then pull off the rest of the backing as you go.
• Depending on the width of the sill and the flashing, you may have to overlap two rows to get the necessary coverage.

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Install sill pan

It’s possible to place the new door sill (caulked) directly on the flexible flashing. But for further protection, and especially in wet locations where rain will splash against the door bottom from all angles, use a sill pan as well.

• Clean the joint overlaps with PVC cleaner, then lay the parts in place and weld the seams with PVC cement.
• Before you go any further, check the floor under the door for level.
  • Sweep the floor free of debris and use a straight board and a 4-ft. level.
  • The doorway should be within 1/4 inch of level over its width. Correct larger variations with two long, tapered shims placed directly under the sill (use treated wood on concrete).
• Fill any voids with silicone caulk, creating a draft-free seal.

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Caulk and install the new sliding door frame

If you have a “knockdown” (not preassembled) door frame, assemble the frame following the manufacturer’s instructions. If the door is prehung, remove the panels so you can install the frame without their added weight.

• Dry-fit the assembled door frame in the opening to ensure everything fits, then pull it back out.
• Apply two beads of silicone caulk along the length of the threshold.
• Set the bottom of the frame onto the caulking, then tip the frame into the opening.

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Square and fasten the frame

• Center the frame in the opening and screw it into place, using a level and shims to square it.
  • Note that the shims will overlap behind the frame’s pre-drilled holes. This will allow the fasteners to hold the shims in place.

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Tip in the glass panels

• Tip the stationary panel into the opening and position it against the side of the frame.
• Install any angle brackets to anchor the stationary panel.
• Check the frame for square once more. Make any adjustments as needed.
  • Walker points out that adjusting the frame and panels can be frustrating, especially for a novice.
  • “It takes a lot of shimming and adjusting,” he says. “There are a lot of variables that can affect the action of the door upon final installation.” Keep at it, and you’ll get there eventually.
• Tip the operable panel into place and screw the inside head stop to the top of the door frame.

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Adjust the door

• Slide the door slightly open and adjust the roller heights until the gap between the jamb and the panel is consistent.
  • Open and close it a few times to make sure the operation is to your liking.
• Install the handle and the locking hardware.

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Finish the Inside

For Walker, the interior and exterior trim is the most satisfying part of the job. He loves “trimming everything up afterward and making it all look nice and like it was always there.”

• Standard slider doorjamb depths are designed to fit standard 4-9/16-inch or 6-9/16-inch thick walls (2×4 or 2×6 studs plus 1/2-in. drywall and sheathing).
  • • Cut the top piece to fit first, then shim it and nail it in place.
    • Then, install the side extension jambs.
    • If your walls are thicker, you’ll have to add extension jambs, as shown in the photos.
• Leave an even 1/8-inch reveal (back set) between the extension jamb and the doorjamb.

• Insulate around the frame with fiberglass packed tightly against the exterior sheathing and more loosely near the drywall.
• Add interior trim around the door, leaving another 1/8-inch back set between the trim and the extension jambs.

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Finalize the outside

• Typically, the new door will be smaller than the one you removed. This will leave a gap you’ll fill with exterior trim.
  • Cut filler strips to fit between the door frame and the siding with a 1/8-inch gap on both sides, then fill the gaps with silicone caulk.
• Rip the trim slightly narrow to leave 1/8-inch expansion gaps on both sides.
  • Seal these gaps with a high-quality acrylic or silicone caulk.
• Cut a threshold support block to fit between the deck and the siding, then slip it into place and nail it.
• Finish your installation by securing a 3/4 to 1-inch thick piece of cedar, treated wood or composite material directly under the overhanging lip of the threshold to support it.
  • Some manufacturers offer an aluminum support strip to use instead.

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About the Expert

• Brandon Walker has been in the construction industry for more than 20 years. After running his own company, he decided to advance his skills as a Superintendent with ASAP Restoration.