How Do You Replace a Patio Door?

By Roxy FavrettoLast Updated April 22, 2019
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Sliding patio doors are fixture of homes across the country, and it's no mystery why. They're convenient, practical and can improve any room with a beautiful view outside. However, if you have an older house, your patio door may not be holding up as well as it used to. Maybe the door has started to stick rather than slide, or maybe it leaks during heavy rain or allows too much cold or hot air to seep inside. At a certain point, no matter how good your old door was, replacement becomes a must.

The price of a patio door can be high, and the cost of hiring someone to install it can raise your bill even more. However, you can save some money by doing the replacement project yourself. Between using your own labor and selecting a highly-rated patio door that can save on energy and maintenance costs, you can make replacing your patio door an affordable project, and the result is a more secure, comfortable and beautiful home. While the installation process isn't easy, it is doable if you break the process down into a few steps.

Project Overview

Installing new patio doors may seem intimidating, but it's not much different from a window installation project. Sliding patio doors are considerably larger, and installation requires intermediate to advanced carpentry skills as well as a few willing pairs of hands to help you out, but overall, the key concepts are the same. If all goes well, you should be able to complete this project in a day.

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For this project, you need basic carpentry tools, including clamps, a power drill, 4-foot level, reciprocating saw, miter saw and a pry bar. While you'll need to purchase a replacement door, it's best to wait until after taking out your old door and measuring the opening before buying it. You'll also need house wrapping, flexible flashing and a PVC sill pan to help with waterproofing, PVC cement, low expanding sealant and wood shims.

Taking Measurements

Before you do anything, you need measurements for the area where you'll be replacing the door. First, remove the trims on the interior part of your door and set them aside to reinstall later. When measuring for width, use the distance between the door jambs. For height, measure from the top of the opening to the subfloor below the doorsill.

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Getting this step right is important. If you end up measuring the underlayment — a secondary layer of plywood or particleboard that the doorsill doesn't fully rest on — you could end up underestimating the size of the space.

Removing the Old Door

This is the part of the installation project where helping hands are vital. Each panel weighs about 100 pounds, and you need to take extra care in removing them, even with help, to prevent injuries. Take out the moving panel first, and then move on to the stationary panel. The process may vary depending on the design of the panels.

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Take out the exterior trim (if any), and then pry and pull the old frame from the outside. This is also a good time to measure the opening again for height, width and diagonal length. Check if the opening is plumb, level and square, and then make corrections if necessary.

Installing the New Door

Install a house wrap and flashing on the bottom and the sides if you deem it to be necessary. You can also add a vinyl sill pan at the bottom of the frame to keep out water splashes, even in heavy rain. Apply PVC cement when setting the sill pan sections to keep them in place.

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With the wrap and flashing positioned, start assembling the new frame. Apply two to three beads of silicone caulk along the opening, and then tip the new frame into the opening. Center the frame and screw it into place. Using wood shims, make sure the frame is level and square before installing the rest of the door, including the sliders, panels and stops. Make final adjustments before applying the final caulking.

Adding filler strips should fill the gaps between the siding and the frame. Use silicone caulk to ensure a quality seal and then reinstall any trims or other elements on the inside and outside the frame to finish.

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