Q. When I install prehung and precased doors, I use shims to plumb both the hinge and strike jambs before nailing off the casing. But I've been on jobs where the carpenters plumb the hinge side of the door and then nail the prehung casing solid to the studs without using shims. This method certainly seems faster, but is this kind of installation strong enough, and does it allow enough room for expansion?
A. Gary Katz, a finish carpenter in Reseda, Calif.; moderator of JLC Online's finish-carpentry forum; and a frequent contributor to JLC, responds: I've installed thousands of hollow-core prehung doors in apartments, condominiums, and housing tracts — all without shims.
If the rough openings are sized 2 inches larger than the net door size, and if the door frame is roughly centered in the opening, the remaining gaps between the jambs and the framing are only 1/4 inch to 3/8 inch wide. Four 2 1/2-inch-long nails through the jamb at each hinge — a pair above and a pair below — and pairs of nails through the strike jamb about 14 inches on-center into the trimmers or jack studs, along with 2 1/2-inch nails through the casing into the studwalls, are more than enough to secure a hollow-core prehung door. A single 2 1/2-inch-long drywall screw through the top hinge and into the trimmer seals the deal.
The purpose of not using shims is for speed, though, not expansion. On the jobs I worked, I wasn't being paid for care, but for completion. Still, we never had callbacks and those doors still work fine.
However, if you're installing a solid-core door, whether it's prehung or not, always use shims. And for hollow-core doors in custom homes, shims are a good idea, too — who knows when someone will decide to switch out those lightweight doors for heavier ones.
On a standard 6'-8" door, I like to shim just beneath each hinge, and I put three sets on the strike side: one near the top of the door, one behind the strike, and one near the bottom. And on every door, I install long screws through the top hinges that sink securely into the trimmer.
Those screws do more to secure a door than any stack of shims or any number of nails.
