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Install a Prehung Door

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Step 3: Position and Fasten the Jambs

Place the door assembly in the opening (with the hinges where you want), and check that it can sit plumb:

Building Smarts

Check that bottom gap! If you have carpet (which is common), or the floor slopes up toward the center of the room (which is rare), the door needs a larger gap at the bottom. Houses with forced-air heating and cooling should have supply ducts and return ducts in each room. If the builders cut the door bottoms short so air can circulate in the absence of a return duct, cut the new door to match the previous one.

  1. Check the gap between the jamb and the framing—ideally, it's about 14" all around. The gaps allow room for shims, which will hold the door plumb. If the gap is much larger, cut a hunk of plywood and nail it behind your shims.

  2. Check that the jambs are flush with (or at most 18" above) the drywall around the opening. A level (or a straight piece of wood) is useful to check that the door is flush in the opening. Do this often while positioning the door.

  3. If the jambs are not flush, tack the jamb extenders mentioned earlier to the edge of the jambs. If that makes the jambs too wide, attach the jamb with the extenders flush to one wall, and hang the original jamb beyond the other wall, where you can plane it afterward. In this position, the plane won't hit a nail.

  4. Check for at least 14" bottom clearance when the jambs rest on the floor (but see sidebar).

  5. With the jambs resting on the floor and flush to the walls, insert a pair of hinges between the jamb and the stud, behind the top hinge. Hold the level against the jamb, checking that it is plumb all the way to the floor. Check that the opposite jamb has room for shims.

  6. Drill through the hinge jamb and tack through the shims with two 212" finishing nails. (Keep the heads up in case you need to pull the nails.)

Slide shims behind the center hinge. Move the shims in and out until the jamb is plumb, and tack through the shims. Repeat at bottom hinge, near the floor, and at the top of the hinge jamb. Keep checking that the jamb is plumb and flush to the walls. If necessary, pull the nails, adjust the shims, and readjust.

Check that the top jamb is level, and repeat the shimming-and-leveling ceremony on the opposite jamb. Again, start from the top and plumb downward with the level. While testing for plumbness before nailing, push the jamb tight against the shims and stud.

When all shims are tacked into place, check that …

  • The door has equal gaps at the sides and top.

  • The jambs are tight to the shims.

  • The jambs are plumb and flush to the walls.

Now pound in the nails and set the heads.

Step 4: Finish the Door

If your door is grazing the floor, remove the hinge pins, lay the door on sawhorses, and saw across the bottom, using a square or a piece of wood to guide the saw. To reduce splintering, score the door veneer exactly on the cut line with a utility knife before sawing.

The door may come predrilled for the doorknob and latch. Otherwise drill and install the hardware.

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Excerpted from The Complete Idiot's Guide to Simple Home Improvements © 2004 by David J. Tenenbaum. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.

To order this book visit Amazon's web site or call 1-800-253-6476.


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