Hollow-core door: what part of the bottom is solid?

17 years ago

I am looking into cutting a hole into the bottom of a new sliding door, to make a "custom" cat flap that will blend in with the rest of the door. When cutting from the bottom, how much is normally solid? How far do you go before you are in the hollow part? If the cut-out portion is 5 inches high, will the top of that then be in the hollow area? It'll make a difference figuring out how it is to be hinged.

This will be an interior door; either oak veneer slab or 6 panel MDF (which choice would then be painted). I am thinking of just making a squared U-shaped hole, open to the bottom, then attaching a flat piece flush with the front, and with a hinge on the inside. Because of the thickness of a typical door, though, I'm not sure if there is a better way to go about this. The back would show a recess, but that side is just the mudroom and the view does not matter.

I have a newly remodelled kitchen and don't want a tacky plastic cat flap in a new door. The goal is to make this look as unobtrusive as possible.

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Jon1270

17 years ago

The previous owner of my house built a cat flap into the door to the basement, made of 3/4" pine and hinged at the top. I don't know whether his cat used it, but ours refused. I think a cat door is likely to be acceptable (to the cat) only if it's extremely light weight and easy to move.

The solid wood that runs around the edges of a hollow core door acts as a frame that gives the door its shape and stiffness, and I think cutting a large enough hole, all the way to the floor, would cut the bottom frame member completely in half and pretty much ruin the door. It's probably possible to cut out the whole bottom rail and from between the door skins and install a larger one that would accommodate the hole you're describing, but it would be a pain to do. I'd be looking for plan B.

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Comments (6)

brickeyee
17 years ago
The bottom member is rarely more than about 2 inches high.
Better to cut above this and add in some blocking on the 3 sides, then install the cat door.
Cutting the bottom member is a really bad idea.
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linnea56 (zone 5b Chicago)
Original Author
17 years ago
Ah! Thanks. So cutting through it would ruin the stability of the door. Makes sense.

Are the sides of a hollow-core door about 2 inches thick as well? Or thinner? Since it's to be a sliding door, I also thought about cutting off one corner, cutting up from the bottom, and then in from the left side. This would be on the advancing edge. This would not be flapped, just open. I thought if then we buy the door a little oversize, we could pull it more closed to seal off this small
opening if needed. It's to be a surface mount system, like a barn door, mounted on the side away from the kitchen, so door would be oversize on the pantry side and overlap the doorframe by whatever we decide. The hardware is from Johnson Hardware, that makes sliding door systems.

We haven't bought the door yet. We could go with a solid door: I looked at some that were oak veneer with a particle board interior, and edges in pine. The door/hardware company was urging a solid core door on me, but I am concerned about the weight with a sliding door. I have had nothing but hollow core doors in every house before. (We did not discuss the cat-flap issue!)

Thanks for your help: suggestions are welcome. Both on the door in general and the cat-flap.
mightyanvil
17 years ago
I would be concerned that the cat flap would keep the door from sliding into its pocket. There are different kinds of hollow core doors. If it is a flush birch veneer door it will not be difficult to cut an opening and add blocking. If is a Luan Mahogany door it will probably be difficult. Personally, I would avoid using any hollow core door in a house. Solid doors are a bargain since they offer so much better security, sound separation, fire protection and last longer. You should consider MDF doors too.
linnea56 (zone 5b Chicago)
Original Author
17 years ago
The kinds we are looking at are oak veneer slab, either hollow-core or solid. The only thing stopping me from getting the solid is concern over weight. I hadn't thought of sound separation. You mean I could actually do laundry while watching TV two rooms over? That's a novel thought!

Aren't MDF doors hollow? That's what the house came with (the boring old 6 panel colonial, textured to imitate wood). I would love to get rid of them all, but that's too many doors to replace.

The more I think about this, the more I hate the idea of cutting a hole in this soon-to-be-nice new door. But otherwise I would have to leave the door open a few inches! I thought of cutting one through the drywall in a tiny closet next to this door, but found there was a cold air return exactly in the wrong place, opening onto the laundry room side. And I would still need a cat door or opening in the closet door.
brickeyee
17 years ago
There is a cat door in a hollow core swinging door going to the basement in my house now.

In any hollow core door you need to avoid cutting the outer wood. It is the only thing really giving the door any strength.

Most pet doors are designed to be supported on all 4 side anyway (if you are going to actually install a pet door) and stick out slightly to hide the cut edges in the door (some over 1/4 inch).
If you just want a hole, cut it into the face and run up to the edges but not through them, then fill in the other two sides.
If you use a router to cut the face plies you can leave a pretty clean edge that should not look bad.
A flush cut top bearing bit running against a piece of scrap clamped to the door will help prevent any tearing of the door face. You need to cut all 4 sides this way, one face of the door at a time.