“The best-laid schemes o’ mice an’ men,” wrote the poet Robert Burns in 1785, “gang aft agley.”

Nobody knows what that means (which proves the poet’s point), but maybe Burns was a door installer. “Agley” is as good a word as any for a door frame so crooked that nobody can make the door fit.

It starts with the framing. In theory, if you snap a line on the subfloor, frame your wall flat on the floor, stand it up, nail the plate to the line, and plumb and brace both ends and the middle, your rough door opening should describe a flat rectangle in space. In practice, though, plates and studs can be crooked, levels can lie, and door jacks can get smacked around by accident the next day.

So your finish carpenters should check every opening before they install a door—whether they’re building a custom jamb or plugging in a pre-hung unit. Plumbing each leg of the door frame, cross-taping for square, and cross-stringing for flatness are the standard checkpoints. When it’s not right, reach for the recip saw and sledgehammer.

Even after drywall, you can sometimes undercut a wall plate and tweak the opening into some semblance of symmetry. But if you want to spare your finish crew this kind of struggle, make plumb, square, and flat door openings one of your quality checks on the framing crew, before you sign off on their work.

Legs Akimbo: For whatever reason, rough door jacks are sometimes out of plumb in different directions and door openings are neither flat nor square. When that happens, doors won’t close properly and the results aren’t pretty—or functional.

Credit: Harry Whitver

Checking for Square: The test for square is simple. First, stick a framing square in the door corners and see how things look. Then cross-tape the opening. If it’s a true rectangle, the diagonal measurements across the opening should be equal.

Credit: Harry Whitver

Cross-Stringing for Flatness: Run strings across each diagonal of the door opening. If the strings don’t touch, the opening is not flat. Find out which of the door jacks is out of plumb (could be both). Cut the nails holding the plate to the deck and whack the framing around as needed. Then re-nail.

Credit: Harry Whitver