Installing New Doors

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A prehung door arrives with bracing to hold the frame square and hardware like hinges fully installed. Measuring a New Door Blank Most homeowners are replacing a door that's been damaged or cut short to fit existing flooring, a simple enough fix if you take the time to measure. If the door is short because you've changed flooring, measure from the door top to the new floor height. Write down the height for later reference. Push out the hinge pins with a punch, tapping up from the bottom. Have a helper hold the door as the pins come out. Lay the door on sawhorses or work table. Remove the door knob assembly and hinge leafs. A new core—a door without holes, hinges, or lock mechanism—can be ordered from a lumberyard or home center. Just measure the existing door for the right measurements. When you have your new core, lay it on top of the old one. Check the tops of both doors to see if they're grooved or chamfered a bit. Doors are usually beveled from three to five degrees on the "strike" side of the door where it hits the door stops. Make sure both doors have the bevel running in the same direction because it's imperative that your new door face the same direction as your old door. The hinge mortises must be cut on the correct side and face of the door to achieve this. Align the doors perfectly to see if the new one will fit into the jamb. If it's larger than the old door by about an eighth of an inch on the sides, it will have to be cut down using a circular saw and a straightedge—don't worry about the top and bottom height just yet. If it only needs about an eighth of an inch taken off the sides to make it fit, use either a jack plane or a belt sander to size it. A belt sander is useful to knock the sides down but will make a lot of dust. The jack plane will also trim it to fit and isn't as messy. Place the door on edge using a portable vise or pipe clamps to act as feet and hold it vertical for planing. Once planed, put the core in the jamb to check for fit. When installing a prehung door, it's important to shim behind the hinges and check for level and plumb before nailing. Cutting to Fit Once it's cut to the proper width, it's time to cut it to length or width. Cutting the bottom is much easier than cutting the sides, so try to get a width that fits to within 1/8 inch or so on each side. When cutting the length, make sure you know where that beveled top edge is—you don't want to disturb the bevel that helps the door close properly so you'll only want to cut it to size from the bottom. Now refer back to that door height you wrote down before you removed the existing door. The new height is the measurement from the top of the jamb down to the floor minus 1/2 to 3/4 of an inch. You usually want about a 1/2-inch opening at the bottom of the door so it glides over obstructions like carpet. The 3/4-inch opening gives more clearance if the floor isn't level. Before you trim the bottom, wrap masking tape around the door where you'll cut to keep the surface veneer from splitting. Mark the cut line, then score it with a sharp utility knife. Use a straightedge or a straight 1x4 clamped to the door to guide the cut with the circular saw. Check for equidistance from the edge of the saw guide to the mark across the entire width of the door bottom.

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