Installing a pre-hung interior door

MATERIALS: Prehung door, shims, #6 and #8 finishing nails, 2 1/4-inch screws

TOOLS: Stiff putty knife, small pry bar, large pry bar or crowbar, level, hammer, nail set

Installing a prehung door is easier and faster than starting from scratch because most of the difficult operations have already been completed. All that’s left is to pop off the trim from the existing opening and remove the jambs. This may sound and look like major work, but all it takes is time and muscle. Once the jamb is out, putting in the new door is a matter of shims and a few finishing nails.

1 REMOVE THE EXISTING DOOR. Start by loosening the trim with a stiff putty knife, then use a pry bar and a block of wood to remove the trim without damaging the wall. The head and side jambs are usually nailed together. It's easier to remove them from the opening at the same time. Pry the side jambs away from the studs. Then pry down the head jamb.

2 SLIDE THE PREHUNG DOOR UNIT INTO THE ROUGH OPENING. Put the door in the opening and slide it until the jamb is flush with the wall. Make sure that the door opens in the desired direction, and into the room you want it to swing into. Remove and reposition, if necessary.

3 SHIM THE JAMB PLUMB, LEVEL, AND STRAIGHT. The door frame is slightly smaller than the opening it fits in to allow for adjustments. Slip shims under the side jamb until the head jamb is level. Then shim between the side jambs and the studs to fill in the spaces between them. On the hinge side, start with the bottom and top of the jamb. Then shim between the hinges and the studs, positioning the shims so that about half the shim is above the hinge. (This will help you later when nailing.) Make sure the jambs are plumb. On the latch side, shim at roughly the same places and at latch level.

If you’re installing over carpet, remember to account °r the thickness before you hang the door. You may have to trim the bottom in order for the door to swing properly.

Stuff you won't need - Most prehung doors have packing that you should remove before you put up the door. Wrappers and plastic banding are obvious, but you also may find a plastic plug in the lock mortise. (This kept the door from swinging open during shipping.) The strip of wood across the bottom of the opening is there to keep the legs (vertical pieces) from coming loose during shipping. Pull it off before you hang the door.

4 NAIL THE DOOR FRAME TO THE STUDS, Drive #8 finishing nails through the frame, through the shims, and into the studs. Drive two nails through each shim about an inch from each edge of the jamb, with one about 1/2 inch above the other. Before driving the nails home, open and close the door, and make any necessary adjustments. When you're happy with the way it works, drive and set the nails.

5 NAIL THE TRIM TO THE JAMB AND STUDS. Drive #6 finishing nails through the trim and into the studs behind the wall, spacing the nails about 16 inches apart. Trim any exposed shims by scoring them with a knife and then breaking along the line. Cut and install trim on the second side of the door.

Installing split-jamb interior doors

SPLIT-JAMB PREHUNG DOORS WORK WELL in situations where the rough frame is wider than a standard opening. They have a two-piece jamb that sandwiches the wall. One added advantage of a split-jamb door is that the casing is already attached, so no mitering is necessary.

1 SEPARATE THE TWO HALVES OF THE JAMB. Set the "slip" (or unhinged) side in the room where it will be installed. Put the hinge stop side in the opening. Tack through the casing near the top. Block and shim near the hinges on both jambs and above the jamb. Plumb and square the unit. Nail through the jamb [not the stop) into the frame with 6d finishing nails.

2 CUT THE SHIMS FLUSH WITH THE FIRST HALF OF THE JAMB. Inset the other slip of the door into the first half and gently push it into place until the casing reaches the wall. Use 6d finishing nails to nail through both halves of the jamb right in the center of the stop. Nail the casing to the wall with 4d finishing nails.

Installing molding for interior doors

MATERIALS: Molding, #6 and #8 finishing nails, glazing putty or wax stick for filling nail holes

TOOLS: Hammer, tape measure, marking pencil, combination square, miter box, nail set

LIPSTICK MAKES MEASURING EASY - On a door trim, rub lipstick against the point of the miter. When you put the leg against the miter, the lipstick makes a mark where you need to make the cut. Use the same technique to install drywall. To lay out the hole for a switch or outlet, rub lipstick on the junction box. Put the drywall in place and push gently in the general area of the box. You'll get a bright mark on the back of the drywall, showing the location of the box.

When installing door trim, some carpenters begin with the legs (vertical pieces); others prefer to hang the top trim first. Installing the top first has the advantage of offering precise control over the most finicky part of the installation—the miters. Once the top trim is up, install the legs one at a time, positioning each so that the miter is perfect. If you install the legs first, you’ll have to fit the top trim on both miters simultaneously. Unless both miters are perfect and the legs perfectly parallel, you’re bound to get gaps you can’t close.

Lay out the reveal. The door trim is never flush with the edge of the jamb; typically it sits back from the edge by about 1/8 inch. The space, or reveal, leaves enough room for the hinge barrel and provides a margin of error if the jamb dips. The frame on a prehung door is likely to have a layout line on it that marks the edge of the reveal. If you work on an unmarked door frame, set a combination square to 1/8 inch, and guide it and a pencil along the frame. Mark the reveal on both sides and above the door.

Getting the trim to fit is the last step in hanging a door. The molding around a door is one of the most visible finish elements in a room.

1 MEASUREAND MITER THE TOP TRIM. First cut a 45-degree miter on one end of the top trim piece; hold it in place to mark the inside point of the second miter cut. Lay out the cut with a combination square, and cut it with a miter box.

2 NAIL THE TOP TRIM IN PLACE. To help position the trim, miter two scrap pieces of molding, and clamp them in place along the sides of the door frame. Cut and place the top trim and adjust as necessary to get a tight miter. Nail the top trim into the jamb. (Leave at least 1/8 inch of the nails exposed in case you need to adjust the piece later.) Use #6 finishing nails for the jambs and #8 finishing nails through the trim and into the studs.

3 MITER THE LEGS. Mitering a piece to fit can be tricky. Make it easy on yourself by mitering the legs before you square them off. Then place the legs against the frame so they're upside down. This leaves the miter on the floor and the full length of the trim extending toward the ceiling. Mark where the top trim touches the leg and cut the leg square at the mark.

Leave a little extra length on the legs to ensure a good fit. Fine-tuning for a tight fit makes the finished door look great instead of just good.

4 NAIL THE LEGS TO THE DOOR FRAME. Start at the top, holding the leg so the miter closes tightly, and drive a #6 finishing nail through it and into the jamb. Work down the leg, flexing it if necessary so that it aligns with the line that marks the reveal. When you’re satisfied, drive #8 finishing nails into the framing behind the wall. Repeat on the opposite leg, and then set all the nails. To keep the corners tight, predrill and drive a #6 finishing nail at an angle up through the edge of the leg, through the miter, and into the header molding.

HIDE THE NAIL - Hide nails by driving them into one of the grooves in the molding. After you set the nail, fill the hole with glazing putty if you paint. If you stain, stain and varnish before you put up the molding, as shown. After the trim is up, fill the nail holes with colored wax sticks sold in paint departments. Pick a stick that matches the stain and rub it across the nail hole until it is filled.

Victorian molding took a more decorative—and simpler-to-install— approach toward doors. Plinth blocks were installed at the bottom trim and rosette blocks at the top corners. Molding was then cut square to fit between the blocks. An advantage of this approach is that you have no miter joints to cut; another is that it adds Victorian style. Plinth blocks, rosettes, and reversible pilaster trim are available in packaged kits. Install the end blocks first with construction adhesive; then crosscut lengths of trim to fit between blocks.

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