A sliding glass door helps you create a bright, cheerful room with plenty of fresh air and natural light. A wonderful addition to any home, a sliding glass door extends the living space to an adjacent outdoor patio or deck.
Installing a sliding glass door can be a challenging project, even for an experienced do-it-yourselfer. But with enough advance work and careful planning, you should be able to install a sliding glass door within a day.
When to Install a Sliding Glass Door
A large section of the house will be open and exposed to the elements when installing the sliding glass door. Plan the project for a season with warm, temperate weather. Check the weather to make sure there will be no rain on the day of installation.
Always work with an assistant with moving or placing the sliding glass door as it is large, unwieldy, and can weigh between 200 and 400 pounds.
For home security, make sure that you complete the job within one day. If you're unable to do so, make provisions for sealing up the house at night with plywood.
Equipment / Tools
- Caulking gun
- Tape measure
- Utility knife
- Staple gun
- Bubble level
- Electric miter saw
- Hand saw
- 1 double sliding glass patio door, 78-inch by 80-inch
- 1 sloped PVC sill pan, 78-inch (optional)
- Silicone sealant, clear or matching door frame
- Roofing nails, 1-3/4-inch
- Building wrap
- Self-adhesive flashing tape, 6-inch wide
- Plastic shims
- #10 - 2-inch pan head screws
- 1 can of low-expansion insulating spray foam
- Exterior pre-cut brickmold trim
Check the Door Rough Opening
Visually inspect the rough opening header, sill, and each side to make sure that they are straight, level (for header and sill), plumb (for the sides), and that all wood is in good condition.
Measure the Door Rough Opening
Measure the width and height of the door's rough opening. Width and height must be between 1/2-inch and 3/4-inch more than the sliding glass door's maximum frame dimensions.
Measure the rough opening's diagonals in both directions. The two measurements should match if the door opening is square, with a maximum deviation of no more than 1/8-inch to 1/4-inch.
Prepare the Sliding Glass Door
After removing the outer packaging from the sliding glass door, remove corner covers, protective boards, and cardboard. Leave the protective film on the glass for now.
Prepare the Building Wrap
For a door opening that previously had a patio door, remove enough siding to expose 9 to 12 inches of house wrap around the door frame exterior. If the building wrap is still in good condition, it can be reused. Otherwise, continue the project by preparing new building wrap and flashing tape.
- Apply building wrap across the rough opening.
- With the utility knife, cut the wrap across the bottom of the header horizontally from side to side.
- Cut the building wrap vertically down the center, from the header to the sill.
- Fold the side flaps inside and staple them in place.
- Make a 10-inch-long diagonal cut at the top-left corner and top-right corner of the building wrap.
- Fold the top flap up and tape it against the exterior side of the house.
Apply the First Strip of Sill Flashing Tape
- Cut a length of flashing tape 1-foot longer than the width of the rough opening (or, in this case, about 100 inches long).
- Center the flashing tape on the door sill with the adhesive side down. The tape should extend about 6 inches up each side of the door. Leave the adhesive backer on the tape for now.
- Slide the tape toward the exterior so that 1-inch of the tape hangs over the edge of the door sill.
- While holding the tape in place, have an assistant slowly pull off the adhesive backer.
- Fold the tape overhang down against the front of the sill.
- At each of the lower corners, slice back the tape 1-inch.
- With the corners free, finish folding the lower tape overhang against the front of the sill.
- Fold the sides of the flashing tape back against the side of the house.
Apply the Second Strip of Sill Flashing Tape
Repeat the previous step with a second strip of flashing tape, with two differences:
- The second strip will be placed on top of the first strip but will be stepped back toward the interior so that its outer edge is flush with the outer edge of the sill.
- Because this second strip of flashing tape does not overhang the sill, it does not need to be cut back 1-inch at the corners.
Install the Sill Pan (Optional)
For sliding glass door installations that will experience a high degree of exterior moisture, you may decide to add a sill pan under the door to help channel away water.
- Dry-fit the sill pan in the patio door's rough opening.
- Make sure that the pan's front lip overhangs the sill and that its sides fit in the rough opening.
- Remove the pan and turn it over.
- Apply three or four beads of sealant along the length of the sill pan bottom.
- Turn the sill pan over and press it into place.
What Is a Sill Pan?
A sill pan or sill flashing is a sloped door base that collects and channels exterior water away from the interior and back to the exterior. Though a sill pan can be built from scratch from roll sheet metal, for do-it-yourselfers it's usually easiest to purchase and install a pre-built PVC pan.
Add the Drip Cap to the Patio Door
Depending on your type of patio door, you may need to install a drip cap to the door before it is in place. You may need to apply silicone sealant to the back of the drip cap to attach it to the top of the patio door.
What Is a Drip Cap?
A drip cap is an L-shaped piece of continuous flashing over a door that prevents water from leaking into the door from above. Not all doors will have a separate drip cap. On some models, the drip cap may be integral to the door.
Add Sealant to the Door Sill
Add three or four continuous beads of sealant across the width of the sill and up each side, stopping at the ends of the flashing tape.
If using a sill pan, run a continuous bead of sealant along the back fence of the sill pan.
Add Sealant to the Nailing Fins
On the interior-facing side of the patio door, apply generous beads of sealant to the back of the nailing fins.
What Are Nailing Fins?
Nailing fins, sometimes called mounting flanges, hold the patio door against the exterior side of the house and provide a convenient nailing area. Nailing fins may be integral (rigid fins molded into the patio door frame) or non-integral (flexible fins that are delivered folded back and which need to be folded outward before installation).
Place the Patio Door in the Door Opening
- From the exterior, lift the patio door with an assistant and rest it bottom-first onto the sill. Do not slide the door.
- Tilt the top of the patio door back into the opening until the nailing fins make contact with the side of the house.
- Use the hammer to run nails through two of the nailing fin holes at the top corners to hold the sliding glass door in place.
Add the Shims
Place shims into the sides of the door, between the door frame and the rough opening. Do not shim the sill.
Nail Patio Door in Place
On the exterior side, nail the sliding glass door against the house with the roofing nails. Do not nail the top edge yet.
Screw Door Frame Sides Into Place
After drilling pilot holes, drive the 2-inch pan head screws into each of the sliding door sides. Drive screws through every available hole on the sides.
With the hand saw, cut off any shim ends that extend beyond the wall.
Screw Door Sill Into Place
With the caulking gun, inject sealant into the door frame's sill screw holes. Follow by driving screws into the holes. Wipe away excess sealant.
If the doors were not in the door frame when the frame was installed, add the doors now. Once the doors are in place, slide the doors back and forth to check for smooth operation.
Secure Door Header
If the doors slide smoothly, with no binding from the header, nail the top fin into place. Follow by screwing the top of the door frame into the door opening with 2-inch screws.
Add Flashing Tape to Exterior of Door
- Cut two strips of flashing tape as long as the height of the door, plus another 4 inches. In this case, the flashing strips will be 84 inches long.
- Center the two strips of flashing tape vertically on each side of the door, with 2 inches of excess at the top and at the bottom.
- Apply the two strips to the sides of the sliding glass door, directly on top of the nailing fins.
- Cut one strip of flashing tape the width of the door, plus the widths of the two side strips (12 inches) and plus another 2 inches. In this case. cut the strip to 92 inches.
- Apply the tape across the header, directly on top of the header nailing fin.
- Fold down the top flap of the building wrap.
- Cut two strips of flashing tape about 16 inches long.
- Apply the two 16-inch strips of flashing tape to the diagonal cuts in the building wrap.
Add Insulating Spray Foam
Attach the plastic straw extension on the can of foam insulation. From the inside of the house, apply foam insulation between the door and the rough opening. After the foam has dried, cut away any excess with a hand saw.
Install the Exterior Trim
Miter-cut the brickmold trim to fit around the door on the exterior. Install the trim either by hand with a hammer and finish nails or with a power nailer. Caulk between the sliding glass door frame and the trim, as well as between the trim and the house siding.
Add the Door Lock
Per the manufacturer's instructions, install the door lock on the door.
When to Call a Professional
Even for experienced do-it-yourselfers, installing a sliding glass door can be a difficult project. Call a door installation company for help if you don't feel confident that you can install the door within a day or two.