Interior Finish, Millwork, and Door/Window Installation
Drywall and trim
Use 1/2 in drywall on walls and 5/8 in on ceilings or where fire rating is required. Fasteners are spaced about 12 in on center in the field and 8 in on center at edges, kept back from the edge and driven just below the surface without tearing the paper. Joints are staggered between courses, then taped, coated, and sanded. Corner bead protects outside corners. Trim basics: base at the floor, casing around openings, crown at the ceiling. Inside corners of casing and base are coped for a tight fit; outside corners are mitered. Crown molding sits at an angle, so its miter is not a simple 45°.
Doors and windows
Prehung units are shimmed at hinges and strike, then checked for plumb, level, and square before fastening. Rough openings for a prehung door are commonly door width plus 2 in and door height plus 2-1/2 in. Handing is determined facing the door from the outside (the side it swings away from). Windows need a level, square rough opening, a sloped sill pan, flashing integrated with the weather barrier, shims at the jambs, and insulation around the frame.
Worked example: a 2'-8" × 6'-8" door needs a rough opening of about 34 in × 82-1/2 in.
Traps: calling a door left-hand when handing is judged from the wrong side; ignoring the sill pan; overdriving drywall screws.