Installing Exterior French Doors: Prepare the Rough Opening
The first job is to check the opening for plumb, level, and square.
We’ve got the entire opening roughed out for the installation of the door, but we have to do an assessment first because we may need to straighten out the opening a little bit. This is an old house. Is it cross-legged? Is it plumb? Is it level? Is it square? These are important factors when you install a patio door, to make sure the door opens correctly.
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Adjust for Plumb, Level, and Square
The first way I’ll do this is with a laser. The laser that I’m using shoots a 360-degree beam right around this unit. Use the laser to check the plumb and plane of the wall, just to make sure the wall is all in one line. There are many other lasers you can use, such as a rotary laser; I just find this one easier and quicker to set up and use. I’ve got the laser in the middle of the opening. It’s shooting a beam out to the bottom of the studs and plumbing a line all the way up; then the laser is going to connect the two at the top. Looking at the stud, I can see it’s hitting plumb here, but going out of plumb by about 5/8 inch toward the top.
Since the wall is tipping in by about 5/8 inch, we can’t install the door in that plane because the door will have an operational problem. If we try to put the door in perfectly plumb, that’s going to cause a trim problem on both the interior and the exterior. So we’re going to try to split the difference: nudge these walls back to plumb a little bit, not completely, so it doesn’t throw off the plane of the outside wall. We’ll split the difference, about 5/16 inch or so, top to bottom, so the door will operate properly and look right when we’re finished.
I’ve got the level on the wall, and if I move it out about half the distance of plumb, I can push this wall out to it to make the correction. What I’d like to do is pull up this oak, making room for the sill pan, and bump up these plates just a little bit—enough to give me half of the distance I need. If it works, it works; if it doesn’t, I’ll come up with another strategy.
I’ll take a couple of nice, easy taps on the wall to see if it moves. If it moves, great; if not, I’ll hit a little harder.
That didn’t take very much. It’s right on the line.
The other side didn’t move very much, so I have to split the sheathing. Splitting the sheathing releases pressure on the wall, so I can move it about 1/8 inch or so.
Now that the opening is framed, we need to check to see if it’s cross-legged. If it’s cross-legged, it’ll cause an operational problem with the door. We’ll check with a string, and it will tell us what plane we’re in.
If the doors are in the same plane, they’ll open and close together, even if they’re not plumb. If they’re cross-legged—meaning one is out and one is in—they’ll never come together and never seal. That’s why we spend so much time trying to straighten these walls out.
To check for cross-legged, I stick a nail in each corner and run a string in an X-pattern across the opening. The strings are just touching at the middle of the X, so that’s just about perfect. We’re in the same plane, but just slightly out of plumb—maybe 3/8 inch. That’s a lot better than the 5/8 inch we started with.
Let’s check the sill here to see if it’s level. The door has to sit level. And this threshold is nice and level. If it weren’t, I’d have to make a couple of adjustments.
The width of the rough opening is established. Now I have to get the head. It calls for an 80-inch rough opening. I’ll add about ¼ inch of padding at the bottom because I’m using a sill pan and flashing. So I’ll measure up 80¼ inch to the top and mark it, and then measure the width across the top: 72 and 3/16. I can set up a double 2×4 at the top and then do the flashing.
Now that the rough opening is completely set up, we’re ready to install the door. Pull the housewrap back and get ready to integrate that with the sill pan flashing to prevent any water or air from getting under the door. Fold the housewrap to the interior of the stud and tack it into position. I like to cut the housewrap back about 2 to 3 inches in. After we install the door, I’m going to foam up against here and the door jamb to prevent forming a bypass for air to get in. If I were to pull the housewrap all the way in, I’d create a bypass for air and even water. By cutting the wrap to the middle of the stud and putting in the foam after I install the door, it stops it all. It’s a good idea to tape the weather-resistant barrier to the stud to prevent water and air from getting behind it. At the bottom, I fold up the barrier into the opening and cut it flush with the face so that I can integrate the sill pan and flashing.
I like to cut the flashing in a butterfly, using a 90-degree angle, so I can fit it into the bottom corner of the opening.
Here’s a trade secret: To get the paper off the back of the flashing, fold a corner of it paper to paper, and just peel it back. That turns a half hour job into a split second.
I’m going to use sill flashing under the sill pan. If you look at the subfloor, there are a lot of air channels in here. There’s no way I could seal them really well with sealant or caulk. So I use flashing first, then bed the sill pan into sealant so there won’t be any leaks. When I get to the corner with the flashing, I don’t seal it right tight to the corner but come out about ½ inch, then roll it tight to the corner. The corner will be watertight.
The flashing is only 5 inches wide, and I need about 10 inches to cover the sill. So I just lay another layer over shingle style to seal up the whole sill.
I’m going to use a solid sill pan on the bottom of the door. We’ve got a solid hardwood floor. If a storm pushed water against the door, the back of the sill pan would prevent it from getting inside.
I’ve got a redundant system. I air-sealed with the flashing. I’m putting sealant underneath the sill pan. At the seam in the sill pan, I apply PVC cement for a watertight seal. When you’re installing the sill pan, follow the manufacturer’s instructions. Don’t nail through the face of the sill pan; just pin it into position. Don’t be cheap with the PVC glue at the joint; apply a nice liberal coat.
The last thing I need to do is integrate the housewrap into the sill pan. Bring the wrap right over the top of the pan at each side of the opening. Any water that comes down the wall will be shed to the outside.
Now it’s time to install the door. Let’s get it ready.