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Do new replacement doors need to be cut down?

All interior replacement doors I can find seem to be sold in round numbers, i.e. 28", 30", etc. All my doors are measure sizes which are narrower like 27 3/4", 29 5/8" etc. I thought to replace an interior door I would just need to router out the mortises for the hinge and hang it. Will I need to cut the door down to fit?

Re: Do new replacement doors need to be cut down?

Take a tape measure to the actual door to be purchased.

You can cut the new doors down


You can replace the trim and jambs along with the new doors and hardware

Re: Do new replacement doors need to be cut down?

Every door that I have replaced in my life had to be trimmed. The reason: old homes settle, shift and move. Doors go out of plumb and exact openings change with the movements.

If you prefer to replace your door and your door jamb, you may be able to avoid trimming (as long as you don't need to change the rough opening), but it's more work IMO, because it involves installing new casings, baseboard work and drywall work.

A. Spruce
Re: Do new replacement doors need to be cut down?

Doors are always sold in even increments, their actual dimensions may differ. Age of your existing doors will make a difference too. Any door sold within the last 20 years will be about the same size, older homes the dimensions can get weird real quick.

Expect to have to trim the side and bottom of the door to fit properly. Cut the hinge side of the door, as any saw marks you don't feel like sanding off won't be an issue.

Re: Do new replacement doors need to be cut down?

You will also need to put a 5 degree bevel on the leading edge of the latch side for an easy fit. Most slab doors are just that, a slab with no hinge cut-outs, latch mortise or bevel.

What I have done is to lay the new door on saw horses, put the old door on top and transfer all hinge and lock markings, mark the bevel and any top/bottom cuts. Put a 1/8 hole at the center of the lock mortise so when that edge is trimmed you will still have the reference hole.

Make the cuts, clean up any saw marks and sand those cuts to knock off the edge.

Mortise hinges and lock set then finish as desired.

It would take me 2-1/2 to 3 hours without any finishing per door. I would use multiple routers for the mortising to avoid resetting, multiple drill/screw gun to avoid bit change outs, track saw for sizing cuts and beveling.

Good luck

Re: Do new replacement doors need to be cut down?

Door sizes are actually frame opening sizes- the doors are always a bit smaller so the can be opened and closed. Unless it is a custom, something like 29 3/4" is rounded up to 30" which is a nominal 2'-6" door and frame size. 80" is the usual height, but some older homes had slightly shorter doors- some new doors can be ordered to a 78" height as shipped. I just buy off the shelf and cut them down. With today's hollow core doors if you cut more than 3/4" off the bottom you'll have to reset the botton peice. It may need the facing cleaned off, use a sharp chisel and don't worry about small gouges. Carpenter's glue and some spring clamps will reset it. While the glue is drying start on the next door.

Condoman has the right technique so long as the old door fit correctly which with settling it may not have. With extreme care all you need is a skilsaw with a very sharp blade, a sharp chisel, and the drill and bits to bore for the lockset (usually a 2 1/8" holesaw for the knob and either 7/8" or 1" for the plunger body). Sandpaper backed with scrap will smooth the cuts you make and don't forget to round over the cut edges a little so the door facing will not catch if it's brushed up against. Maintain at least 1/2" in the clear on the bottom for HVAC return air on interior doors. Doors ar simply an exercise in planar geometry so any 6th grader should have an understanding of how to do them right but you'd be surprised at how many messed up door installations I find. Think of the big picture first, then cut or adjust and all will be well.


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