Undercut door frames for new flooring

Trim door frames at floor height so new flooring slides neatly underneath, without removing the whole frame.

UD-01Clear the doorway and lift the door offMove rugs, mats and any old threshold strips out of the doorway so you have a clear view of the frame legs. If the door swings across the opening, lift it off its hinges by tapping out the hinge pins with a hammer and screwdriver — this gives you much better access and stops you catching the door as you cut. Lean the door somewhere safe out of the way.

UD-02Mark the cut line using your flooring as a gaugeStack an offcut of the new flooring on top of its underlay and hold it flat against the bottom of the door frame leg. Draw a pencil line across the face of the leg at the top edge of this stack — this is your cut height. Do the same on the other leg and on the door stop (the raised strip the door closes against), since this often needs shortening too.

1 piece · Offcut of new flooring plus underlay

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1 each · Pencil

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1 each · Combination square

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UD-03Cut along the marked lines with the multi-toolFit a fine-tooth wood-cutting blade to the oscillating multi-tool and set it to plunge cut. Rest the blade flat on the marked line and cut straight through the frame leg in slow, steady strokes, keeping the tool square to the face. Repeat on the other leg and on the door stop. Wear eye protection — this makes a lot of fine sawdust.

RULES

1 each · Oscillating multi-tool wood-cutting blade

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KNOW THE RULES

If this is a fire door (common in flats, HMOs and some new-build houses), cutting the frame can break its fire and smoke seal. Building Regulations require fire doors to keep their certified performance, so get advice from a fire-door installer before cutting a fire-rated frame.

UD-04Lever out the cut sections and test the fitWork a chisel or small pry bar into the cut and gently lever the bottom section of the frame leg forward until it snaps free. Slide your flooring-and-underlay offcut under the gap on both legs to check it fits without forcing. If it's still tight, mark a fresh line a couple of millimetres higher and cut again rather than forcing the flooring.

1 each · Wood chisel

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1 each · Small pry bar

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UD-05Clean up the cut edgesSand the freshly cut ends smooth with a sanding block so there are no splinters or rough saw marks left showing. Vacuum sawdust from the doorway and off the top of the remaining frame, since it will get trodden into the new flooring otherwise.

1 each · Sanding block or sandpaper

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UD-06Refit the door and check it swings freelyRehang the door by lining up the hinges and tapping the pins back in. Once your new flooring is down, open and close the door fully to check it clears the floor. If the new flooring has made the floor noticeably higher, the bottom of the door itself may also need trimming — that's a separate job from undercutting the frame.

UD-07Tidy upVacuum the doorway area again to catch any remaining dust and splinters. Bag up the cut-off frame pieces and dispose of them, and wipe down the frame legs with a damp cloth before moving on to laying the flooring itself.

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