Q: I enjoyed John Spier’s article on installing pre-hung doors. What about when the floors will be carpeted?

A: John Spier, owner of Spier Construction, a building and remodeling company on Block Island, R.I., responds: In my article “Hanging Pre-Hung Interior Doors” (Jul/16), I discussed the process I’ve developed for installing interior doors in a fast and efficient manner. Because of space constraints, I did not address the particular situation of when a floor is to be carpeted.

The scenario for carpeted floors starts much the same as with other types of flooring: checking the opening for level across the threshold, as well as front to back on the threshold. But carpeting tends to be more forgiving than other flooring materials, so those assessments are just for general reference. From that point on, my approach to installing the doors is very different, though it is still fast and efficient.

The process I use takes advantage of the fact that the installers like to tuck the carpeting under the door jambs and the baseboard, which gives the installers a bit of a “fudge factor.” If you leave a jamb 1/16 inch short on a wood floor, it sticks out like a sore thumb. But with carpet, that discrepancy is hardly noticeable. For that reason, I cut both jambs to a length that keeps them roughly 3/8 inch off the subfloor. I also make sure that there will be plenty of space to keep the bottom of the door clear of the carpet.

After cutting the jambs to length, I set the hinge jamb on a 3/8-inch-thick shingle butt. I shim and nail that jamb, plumbing it in both directions with a long level.

Next, I release the door slab from the strike jamb and slide a shim or two under that jamb, adjusting the height until there is an even gap between the top of the slab and the head jamb. If the hinge jamb is plumb and the slab is square, then the top of the door should be level. When I’m satisfied with the height of the strike jamb, I insert shims behind the jamb and nail it off, adjusting the jamb until it aligns perfectly with the door stop.

At this point, the only other difference with installing a pre-hung door for a room that will be carpeted is that I keep the shims and the nails close to the floor on both sides. Keeping the shims and the fasteners low helps to prevent the carpet installers from moving the jambs out of position when they come along with their knee-kickers.