I'm looking to install a cat door in a 30 year old hollow core door. The two options I'm considering are 1) the cat-hole




and 2) a traditional flap door


I like the look of the cat hole more but it requires that I cut through the lower framing of the hollow core door. According to my stud-finder, the door is only framed around its 4 edges. I'm concerned if I remove a section of that lower frame, the door will become flexible and twisty. I contacted the maker and they say the hole is OK for hollow doors but I also figured out that many modern hollow core doors have a number of horizontal or vertical stabilzers and mine does not.

The flap door allows me to cut a hole above the frame but doesn't look as nice, IMO, on an interior door that will be seen by others.

Anyone here ever install one of these options on a hollow core door or have any thoughts on cutting out the lower frame and what that will mean to the integrity / stability of a hollow door?

I have done it many times when customizing an off-the-shelf door for a custom installation. Because it is a hollow core door all you need to do is cut your opening exactly as you want it and reach inside the hollow core portion, which is nothing more than cardboard that is laid out in a zig zag pattern between the two skins.
Ou then cut a 2x4 a bit bigger than 1/2 of the cat door opening and create a half an arch anc reduce the thickness of the 2x4 to fit between the door skins. Now make another half and you have the new bottom frame work.
Slide the halfs into the door and a bit of glue and a couple of clamps and you're done. If you have any other questions you can ask or call me or email. Very simple to do and besides, I like the round mouse door better than the flip cat door.

Thanks Jeff. So if I understand what you are saying, as long as the cat hole creates a arced frame around the removed original straight frame, the integrity of the door should be sound? I can buy a prefab cat-hole which is some type of resin or wood whereby the two sides are held together by four screws. See below.



Do you think that is OK enough to keep the door rigid / stable or is it better to do as you advised and make an insert as the frame?

The blue is the 2x4 and the red is the door frame. The blue needs to go in as 2 peices in order to get them inside the door.

It will still flex without the frame being supported.
another trick is to cut the opening and insert the cat door frame and then drill 2 holes, one on each side of the opening through the bottom into the hollow core and spray in the NON EXPANDING WINDOW SPRAY FOAM. Think the can is blue, not red-yellow, that will make the bottom of the door 3 feet thick.

Thanks for the tips Jeff.

Your 2x4 trick is exactly what I was thinking Jeff... I like the idea with the spray foam too!!!

The thing is, B-Roc, whether you do the cat hole or the traditional flap, you'll need to reinforce the empty space around the opening in order to a) sure up the rigidity of the door since you removed some of it; b) give yourself some meat for any screws from the cat door to bite into & c) keep the door from collapsing on itself if there are any type of through bolts involved.

I can tell you so many stories about expending foam ... lol ... 2x4 method is good ... if opening is smaller then 10" you can also use 5/4 x 12 pine wood board and replace existing support with it ... use long screws from both sides and some carpenter glue to make it stiff ....

Quote: Originally posted by Kober

I can tell you so many stories about expending foam ... lol ... 2x4 method is good ... if opening is smaller then 10" you can also use 5/4 x 12 pine wood board and replace existing support with it ... use long screws from both sides and some carpenter glue to make it stiff ....

lol about the foam stories, got a bunch myself.
depending on the door thickness, the style of door, the material of the door (not all hollow cores are wood), what ever the door ID is, that is the thickness of the insert. I called it a 2x4 for description purpose. It can be anywhere from 11/16 to 2 1/8. Is the door original or has it been reskined on one side or both? If so the foam is all you need. If the door is not wood but masonite, YOU WILL HAVE TO ADD WOOD FILLER BLOCKS, and lots of glue.
If you do the foam thing, make sure the door is flat and the thickness is retained during the curing possess which could take a day or 2. You can tell if the foam is cured by knocking on the area you filled and it sounds solid not hollow. Much like knocking on the wall to find a stud.
this is a nice change from kites. If you have access to a press or clamps you can use the expanding foam. The expanding foam will stick to anything and everything much better than the othe foam designed to fill the voids around windows and doors.

Be sure to post a pic of the new cat door, we want to see your handy work.

I never knew you could reskin a door. Is that common and practical? I was going to paint them all but a number of them are banged up and parts of the "skin" have delaminated or split. So I thought maybe I should replace them all. I'll have to look into reskining. Is that done in the home or do you take the doors somewhere? All comments welcome.

Am I the only one who is wondering what the rated wind speed of these little doors is ?

Seriously though, Wouldn't you pay daily in your heating / cooling bill with a hole in the wall like that ? Or is that Canadian thinking ?

Brian, I vote for going through the wall. You can always plug the hole with Sheetrock and you'd never know it was there.

For the doors I'd repair with epoxy. It's structural end easy to work with. You cane en thicken it to plug holes and it will not run.

iPhone word swap! I meant you can thicken it...

iPhone word swap! I meant you can thicken it...

Quote: Originally posted by Bladerunner

Seriously though, Wouldn't you pay daily in your heating / cooling bill with a hole in the wall like that ?

I'm looking at it for an interior (bedroom) door.

-Don, I am thinking about going through the wall. Still trying to figure out if a DYI or off-the-shelf solution is better.

My son gets up about 45 minutes before us and is super loud and turns every light on. I need a better solution than leaving the door ajar so the cat can come and go but I want something that looks nice too as it will go through our bedroom door or wall.

Punched a few doors as a kid and had to fix them. Replacing is easy but not the installation of the hinges or the door knob in a door blank let along stain and finish.
Glueing on a new skin is much easier and cheaper. I do most of them in place.