We own an old house, and would like to replace several of the old existing doors. These doors are between 29 1/4" and 29 3/4" wide, so slightly less than the 30" width that appears to be readily available. I assume that it's fairly commonplace to need to trim doors slightly to fit existing openings (right?). Is a cheap hollow-core slab door (like this one from Home Depot likely to be able to be trimmed by this amount (up to an inch) and retain structural integrity? Will it look ok if sanded down on the trimmed side and repainted?

I gather from this previous question that trimming this amount from the top or bottom of one of these cheap doors is not a good plan. Is the same true from trimming from the side? Should I not attempt this?

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    If you take the door molding off and verify you have some extra space, it might be easier to just take off the whole door and casing and replace the whole thing with a prehung door unit. Hinges will already be cut and set correctly and it will fit properly in the opening.
    – Milwrdfan
    Commented Sep 20, 2023 at 4:16
  • I didn't see it mentioned but I would recommend using the old door as a template (assuming it fits well.) Center it as best you can on the new slab.
    – JimmyJames
    Commented Sep 20, 2023 at 20:26

2 Answers 2


The typical amount of material that is around all 4 sides of the doors that is structural for holding screws for the knob latch and hinges is about 1". It can vary a bit from there. You may find doors with wider wood or MDF around the perimeter, you can check for yourself by looking at the top and bottom of the doors. The ends of the side pieces run the whole length of the door while the top and bottom pieces are cut between the sides.

Fo a hollow core door, I would not cut off no more than 1/4' off of ether side so it will leave 3/4" for screws to work with. Looking at the ends will give you a better idea how much can be removed and still leave the 3/4" needed for the screws.

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    depending on your toolkit you can just cut filler pieces and add them to the door if you reach a point that doesn't have any structure. These are paint grade doors after all. Commented Sep 20, 2023 at 3:37
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    I have shortened such doors by simply cutting across the hollow part, taking the cut-off part and peeling the skin off, and gluing the remaining "structural" part into the new bottom. Obvs doesn't work well for those 6-panel type hollow doors, but plain old slab doors it does.
    – Huesmann
    Commented Sep 20, 2023 at 11:26
  • Cutting into the hollow, I have done many times before, glued and reinserted a new piece or cut the skins off the original and glued it back in. I have never attempted to cut and reglue a side, never needed to. I would try if needed, but to keep the edge perfectly straight in a non- shop environment, as in doing it onsite, would be a task. One shot, it better be right.
    – Jack
    Commented Sep 20, 2023 at 14:30
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    @Jack It's not actually that difficult as long as you have a good set of clamps and a suitably-sized object that's within tolerances for "straight" (for instance: another door) to use as a guide. But beyond a certain point it gets to be easier to just build a new door the size you want.
    – Perkins
    Commented Sep 20, 2023 at 18:10
  • I'm not sure how they did it, but when my sister and brother in law had new interior doors installed every one was trimmed in both dimensions because every doorway was a different non-standard and (I think) slightly off square size. I'd think a table saw would have been the best tool for that job; but didn't see one on site when I visited on the day the work was being done. Commented Sep 20, 2023 at 21:22

I would have just left a comment, but I don't have the reputation. I am an experienced amateur woodworker, but not a finish carpenter. If you try this, it's easy to exceed your skill quickly if something unexpected happens. Doors and windows are probably the most difficult finish carpentry tasks.

The person who suggested replacement with a pre-hung door probably has the best idea, as this requires less skill, though you will probably have to trim the bottom.

If you replace an existing door, you will need to mortise in the existing hinges. That will require either a router or skill with a chisel, or both, plus skill in marking the hinge locations. Chances are, the door will not be square in the frame on an old house as well, and you may need experience in scribing the new door to fit.

If you decide to go ahead, a solid core pine door might be a better starting point. The electric planer is the correct tool for removing small amounts of wood (1/16" at a time maximum) from the door edge. On real wood, it may cause some chipping of the end of the cut unless a scrap block is clamped on the end. For removing larger amounts, the tool of choice is a track saw, but this is primarily a professional tool. A circular saw held against a board or preferably an aluminum saw guide will do OK.

Score the edges of the cut with a knife before cutting to prevent any splintering of the wood when cutting or planing unless you use a track saw. Make a light knife cut followed by a heavy cut. Many people also apply blue tape on the cut line.

Of course, you can also do this with hand tools, which takes more skill as well to do a good job.

Keep in mind a table saw and chisel are likely the most dangerous power and hand tools, both can amputate fingers, hands, etc.

If you are new to an electric planer or circular saw, practice on a 2x4 first. A planer will take getting used to produce a straight edge. Coarse sandpaper is a slower but more forgiving option.

Another option is to consider repairing the existing door. Yes, the question is on replacement, but you may not have considered how easy a repair could be. It is possible to get specialty plywood to completely re-skin a slab door, though not usually at a big-box store. This needs to be very thin or the door will bind against the stop/jam if you add plywood on that side. You can also use bondo and/or spray foam to repair holes. This is a an approach that involves less skill, tools, and surprises. Your only tools would be a saw to cut the plywood or veneer to rough size, and a inexpensive palm router with a flush trim bit. You will also need contact cement.

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