How to Extend Frames for Door Openings

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Sometimes door openings are not the right size for the doors you want to put in them. That creates a problem as you need the door to fit snugly. It means you have to extend the door frames in the door openings. Although this will usually be on the vertical, it can also happen that you’ll need to lower the lintel to accommodate a shorter door.


Measuring the door openings exactly is possibly the most crucial part of the entire process. Measure the door opening horizontally at the top and bottom of the door and at several points in between. Make a drawing of the door openings and write the measurements on them.

Ideally, there should only be minimal variations, but this can depend on how much the house has settled. After this, measure the new door at the same places so you know just how far you have to extend the door frames.


When choosing wood to use for extending the door frames and reduce the door openings, go for the same width and style of lumber as the wood that’s already there. Where the door frames are painted, this might generally be pine. If it’s plain wood that’s stained you might need to spend more on better-quality wood. Don’t skimp as it will be obvious and ruin the effect.


On the table saw you should adjust the fence so you have the width necessary to make the addition to the door jamb. Remember that you’ll need to extend the jamb on both sides for the door to look square and even; take this into account when cutting.


Remove the old door and then the trim from the door jambs. If there are any bumps on the paint, sand them down before you proceed so that the surface is smooth and completely flat.

Start by dry fitting the pieces you’ve cut to check that they fit correctly. If not, make all necessary adjustments. After this, apply glue to the back of the wood and press against the existing door. To secure in place, use finish nails, keeping the wood square on the door frame. Countersink all of the nails and use a small amount of wood putty to hide the holes. Sand level after it’s dried.


Once the glue has dried, you can prime and paint the new wood, or simply stain and finish, so that it blends in with the rest of the door frame. Reattach the trim after cutting where needed. Attach the new door.


If you need to lower the lintel, use the same methods as you would for extending the door frames. Apply the wood in the same manner. Depending on how far you have to lower the lintel, you might need to use several pieces of wood and then add a panel on each side to cover the edges.