Sealing the Sill
There are two approaches to applying sealant between the door and the pan. The barrier method assumes that hardly any water will get behind the flashing and sealant, and the little that does will naturally evaporate before causing any damage. The drainage method assumes that water will eventually get behind the flashing (probably due to door failure) and will need a way out.
In my experience, the barrier method is a good choice when you’re using outswinging doors, because their sills are by design more water-resistant. Whenever unprotected doors will be exposed to sustained high winds and lots of rain, I recommend outswinging doors with sill sealant applied using the barrier method.
The barrier method can work with inswinging doors, too, as long as they’re protected by a wide overhang or have limited exposure to wind and rain. But for inswinging doors in moderate-exposure locations or on the second floor of a home, I always recommend the drainage method. In this system, water that manages to penetrate past the sill drops into the pan and eventually makes its way back outside. Our tests show that the approach works quite well.
Regardless of which method is used, there should be squeeze-out all across the front of the door sill (except at the central gap, in the case of the drainage method), as well as in the rear of the pan, when the door is set in place. Too much sealant is always better than not enough.
Installing the Door
Before installing a door that has brick mold or flat casing, I run a bead of sealant along the inside corner of the union between the casing and jamb, pressing the sealant into place with my finger. This helps prevent water from penetrating this vulnerable joint, and the inside location is ideal because the sealant won’t be exposed to UV light or other outside elements. I also apply 1/2-inch-diameter beads of sealant to the backs of the nailing fins or casings, toward the outside edge. With a finned unit, I bed flexible flashing corners into sealant at the two upper corners before installing the unit, giving these joints a little extra protection.
When the unit is tilted into the opening, sill first, the doors should be closed and locked. After completely pressing the unit into the opening, I make sure there is plenty of sealant squeeze-out around the top, bottom, and sides of the door. If there isn’t, I tilt the door back out and add more sealant.
Once I’ve checked the door for level, square, and plumb (a laser level is quicker, easier, and more precise than a spirit level for this), I begin installing shims around the perimeter. To prevent these shims from overcompressing the sash, I first put a couple of shims between the sash in the center of the door. Shims are needed behind all the hinges and across the top of the unit to prevent the heavy glazed doors from twisting the jambs as they swing.
Next, I fasten the unit to the trimmers with 2 1/2- to 3-inch-long exterior screws driven through the hinges, jamb, and shims, one per hinge. I also drive a long screw through the strike plate and shimmed head jamb.
Now it’s time for another string test. After opening and closing the doors to verify that they operate properly, I leave them open, grab some mason’s string, and — following the same procedure described earlier — double-check the unit for cross-legging. Again, the strings should gently touch in the center where they cross. If they don’t, I withdraw some screws and adjust the jambs until the gap in the middle is eliminated.
Nailing fins. Instead of nails, I use 1 1/2-inch exterior deck screws to fasten door units with nailing fins to the wall. Screws are less likely to damage the doors and are reversible. I place them every 9 to 18 inches across the top and both sides. For extra weather protection, I tool a flat bead of sealant on top of the fins. If the nailing fins are the pivoting style, the sealant should be on top of the pivot joints, which are the source of many leaks we’ve investigated. The top flashing laps over the top nail fin, followed by the housewrap.
Casing. If the door has brick mold or flat casing, I use 2 1/2-inch to 3-inch galvanized nails to fasten it to the wall. A metal drip cap set in wet sealant should be installed over the casing, followed by the peel-and-stick flashing. The vertical leg of the drip cap should extend up the wall at least 4 inches, and any screws driven through the metal should also travel through the sealant. After folding the housewrap back down over the drip cap, I seal up the seams with tape.
Once the operating hardware and any accessories that came with the door unit — such as weather-resistant foam pads — have been installed, I perform a final round of door opening and closing to be sure everything operates smoothly. Most doors come with adjustable hinges for fine-tuning the fit, but be sure to check the manufacturer’s instructions; not all hinges operate the same way, and it’s easy to strip their threads.
Gene Summy is a contractor and building inspector in Laguna Niguel, Calif. His company, TLS Laboratories, specializes in rain-related problems.