How to Undercut Door Frames for Flooring

Undercutting the door frame is the neatest way to finish a floating floor in a UK doorway. You take a thin slice off the bottom of the architrave and lining so the new laminate (or vinyl) slides under the timber. The expansion gap stays hidden. Done badly, you leave a wavy cut, nick the paint face, or cut too high and the board rattles in a slot that never closes.

Do this before the last rows go down. Pair with how to cut laminate around door frames when a notch is still needed at a stop or threshold, and the parent lay: how to lay laminate flooring.

Why undercut instead of scribing every board

Scribing around an architrave leaves a cut edge in view. Undercutting hides that edge under wood that was always there. Softwood Victorian and modern softwood frames cut easily with a multi-tool. Do not undercut fire-rated doorsets, steel frames, or rented joinery you have agreed not to alter. In those cases, scribe the plank instead.

Hallways with several doors: undercut every frame to the same finished height so one underlay thickness works throughout (how to lay laminate in a hallway).

Set the cut to finished floor height

1. Build a gauge from your real materials

Stack a scrap of the underlay you will use on a scrap of the laminate (or vinyl). That sandwich is your cut height. Hold it against the frame and rest the multi-tool blade flat on top of it. Guessing from the pack’s printed millimetres alone is how people cut too high or too low.

Choose underlay before you cut: how to choose laminate underlay UK, then how to fit underlay for laminate.

2. Protect and light the work

Dust sheet the room. Softwood dust goes everywhere. A torch aimed along the floor shows the blade line better than overhead light alone, especially in dark hallways.

3. Cut along the architrave and into the lining

Start on the architrave face, blade riding the gauge. Work steadily; let the oscillating tool do the work. Continue into the lining so the plank can pass under the full thickness of the doorway timber. Internal corners often need a sharp chisel to finish the waste the blade cannot reach.

Feel for cables or pipes before you dig deep into skirtings beside the frame. In older houses the skirtings sometimes hide later wiring runs.

4. Clear the slot and test

Vacuum the slot. Slide the gauge sandwich under the cut. It should enter freely with a little play, not jam. If paint lips remain, take another light pass. A tight slot will chip the décor edge when the real board goes in.

5. Lay through and check swing

With underlay down, slide the flooring under the frame and click it home. Open and close the door. If the leaf now rubs the new floor, undercut or plane the door bottom rather than forcing a thinner floor build-up you did not plan for.

Mistakes that wreck the frame

• Freehanding the height without a gauge. One side ends higher than the other and the board rocks.
• Cutting only the architrave and stopping at the lining. The plank then hits a step you cannot see until offer-up.
• Using a metal or coarse blade that burns and tears softwood. Fit a sharp wood blade.
• Undercutting a fire door lining “just a bit”. That can invalidate the doorset. Scribe the floor instead.

When to leave it to a joiner

Stop if the frame is part of a certified fire door, if the lining is metal, or if rot crumbles as soon as the blade touches it. Replacing rotten linings is a different job from flooring. Substrate problems under the doorway (wet screed, bouncing boards) need fixing first: how to lay laminate on concrete, how to lay laminate on floorboards, how to fix squeaky floorboards.

Tools for the wider job: tools needed to lay laminate flooring. If every doorway in the house needs this cut, weigh the time against cost to lay laminate flooring DIY vs fitter.

FAQ

What tool undercuts a door frame for laminate?

An oscillating multi-tool with a sharp wood blade is the usual DIY choice. Rest the blade on a scrap of underlay plus laminate so the cut matches finished height. A dedicated jamb saw works too if you already own one.

How deep should the undercut be?

Deep enough for the plank to slide under the architrave and lining with a small clearance, typically a few millimetres beyond the board thickness plus underlay. You are not cutting a tunnel halfway up the frame. On painted frames, a second light pass often removes a paint lip the first cut left behind.

Can I undercut painted Victorian architraves?

Yes if the timber is sound. Expect more dust and careful work on ornate mouldings. Finish corners with a chisel. If the architrave is loose, refix it after the cut so it does not chatter on the new floor.