If your cat is anything like mine he's probably going to want some extra room at the box entrance (low side). I have the box you described and my cat likes to stand outside the low portion of the box and finish burying her business. For that reason I'd leave at least 12" in front of the box, but it's going to depend on how long your cat is and how much room he needs.
In the drawing below you can see I left some room on one side of the box. This is to allow the cat to get into the area before he has to turn and then enter the box.
Is this closet going to have a regular door on it? Also, how tall with it be? If you have a good bit of height and the cat door is always open then you can probably get by with some foam covered ventilation holes near the top of the closet.

I think you should consider having a deep plexiglass 3-sided pan made so that you can set the litter box inside it. This will protect your walls and also be easy to clean. But, with that setup you'll need a large access door to make removal of everything easy.
Since you're in Or., check with Tap Plastics for plexiglass. They'll either make the plexi pan to your specs or you can have them cut the pieces and you put it together with Weld-On Glue. From experience I can tell you that if you want an attractive, smooth, clean finish on your seams then let Tap do the work. I once built an aquarium refugium tank with the plexi and glue and can tell you it's kinda like working with super glue!
{{!gwi}}

Thanks, Annz, for the tip about Tap Plastics and the drawing!

Yes, I do plan on having room in front of the low side of the cat box. I wasn't sure how much room to leave but I figured 12" at a minimum and maybe as much as 24". Good point about having a little extra room on one side.

The closet is really more of a box that will be 2-3' tall, 3-4' long, about 2.5' off the garage floor. The door won't be full-sized, but it will be as tall and wide as possible so that we have access to the litter to make it easy to clean it.

Thanks again!

We have something like what you described, though we aren't using it at the moment.

We have a run-of-the-mill oak vanity in our guest bathroom, it is probably 4 feet long and whatever an average vanity is wide (22"? 24"?). We cordoned off one half with plywood and cut a small kitty door on the side of the cabinet (next to the toilet- where most people would probably put a trashcan, if you can visualize that). It is not an ideal size for a litter box, but 3 cats have used it over the years without complaint.

We put peel-and-stick vinyl tiles on the floor and up one side, and painted the remaining surfaces (including a "ceiling" we put in) with a pure white, high gloss paint- to make it brighter and lighter and for easier clean up. Even though the cabinet is probably a little on the small side, the cats always used it with no problems. Clean up was always fairly easy too, especially with the type of paint being very easy to clean. We also installed some of that vinyl strip that is a little like baseboard (I don't know what it is called), it is about 4" wide, peel and stick, and it eliminated the sharp corners and gaps where the flood meets the walls- again, a little easier clean up.

We are not currently using the cabinet, however, because our old cat began having additional litter box issues (she has lots of urine related issues- including increasingly foul smell and poor aim), and the cabinet began to smell rather bad (like an old campground outhouse, for lack of a better description). Nothing we used did much to combat the odor- we probably need to retile and repaint, but figure with her issues, probably not in her lifetime; so we switched the location of that litter box to the tub for the time being. The cabinet was used for 8 or 9 years before that with no problems though.

We don't have a ventilation fan of any sort, but there were times that might have been a good idea. We live in a relatively dry climate, and nobody much ever uses that bathroom for showers or the like, so the humidity stays low. If you have much humidity at all, I don't think you would be sorry to have put a quiet ventilation fan in there.

I also thought that the brand of litter we used had an effect on how the cabinet smelled. It seemed like certain brands/types absorbed the odors better and as soon as you took the box out and cleaned the cabinet there was no detectable litter box odor. Then there were other brands of litter that it seemed like more smell remained in the cabinet. Don't know if I'm imagining that or not.

I hope to go back to using the litter box cabinet eventually (will have to be after our old girl leaves us), but I do have a lot of questions about whether our younger cat will take to going into the cabinet to do his business. Cats can be pretty particular about where they potty- I guess the lesson there is that a bigger cabinet might be more to a cat's liking if he hasn't used such a place before.

Thanks, quasifish, for the tips about the high gloss paint and the vinyl baseboard!

Do you know Pinterest? Go to pinterest and search hidden litter box for oodles of ideas.

Good luck on your project.

I liked the link below for people that need to keep the dogs out of the litter box.

Here is a link that might be useful: hidden litter box

Correction--just search litter box for even more ideas. Click on the picture and it will take you to the original site.

Im not totally visualizing it but it does sound like a good idea - creating space where kitty can do his thing however he wants to. He is a good boy for at least TRYING to get in the box. Some cats balk at going into a totally closed off space where there's only one exit... I think this would be minimized by having the space be fairly large (as you were describing - at least a 3 foot sqaure.) I think I'd have at least one panel be a screen or metal mesh for ventilation.

My girlfriend put a large kitchen cabinet (2 cabinet doors and a row of drawers on the right) in her garage. The panel between the cabinet doors and the counter was removed. They replaced it with mesh for ventilation. It backs up to the house and they put a kitty door into the house. It's worked great for them. I on the other hand had a large cat run built of heavy duty mesh, 10 feet long, 6 feet deep and 8 feet high on the side of our house. With doors on each end. We have a large overhang on the house there so 3 feet of the run is covered, just in case it rains. But I live in a temperate climate (no snow here, except well twice in my lifetime and it melted by 9 am).

Thanks, kim_okla, I'll do a search at that site.

kashka_kat and bluesbarby, thanks for your posts. Unfortunately, we can't leave one wall of the closet as screen or metal mesh. We're building this in our unheated garage and there won't be a door, only an opening, between kitty closet and house - in essence, a flap-less pet door. It would be the same as if we left a window open all the time while running our heat or A/C. That won't do.

We originally thought we'd do a regular pet door (with flap) but our kitty is old and I'm not sure he will figure that out, plus as he ages, it may become difficult for him to open the flap.

He's used to accessing his litter through a smallish opening - we removed one of the sink cab doors - so we think he won't object to going through the opening into his litter closet. The opening will likely be a bit narrower than he's used to since it will be between the studs (generally 16" on center) but we can make it as tall as he's used to.

kashka_kat, I didn't realize that some cats balk at going into closed off spaces with only one exit but I don't think our cat is one of them. About half of the time when we open our hall closet door - a 2 x 3 unlit space with only one exit - he dashes inside. No idea why, maybe he thinks it's some exotic place. ;-) He's even been shut inside the few times we didn't realize he was in there, only realizing it when he meowed to be let out hours later. I'm glad you brought this up because it makes me even more confident that he'll be okay with his new litter closet.

As I type this, kitty is sleeping on the ottoman a few feet from me, snoring so cutely! I never knew cats snored but I've never had a kitty live to be as old as he is now (17). And still going strong, according to his vet.

I can't really picture what you are planning to do, but I just wanted to mention that carbon monoxide may be a problem. There should be a good seal between the house and the garage to prevent ANY carbon monoxide leakage. If you don't use the garage as a garage currently, you may be okay.

Hmm, let me try to explain this again because I've obviously confused people.

Imagine an insulated bump-out in the garage with an opening between the studs (no header required) in the garage/laundry room wall that leads into a sink cab in the laundry room. There will be a door on the opposite side of the laundry room connection so that we can clean out the cat litter from the garage. It will be exterior grade (not hollow core) door with weather stripping around it.

If we add a fan - and I think kitty would appreciate it - it will be one-way air circulation only, like a bathroom ventilation fan - air will go out, not in.

The only real difference between this and a regular addition to the house is that it will be cat-sized with an equally cat-sized entry to it from the laundry room. There shouldn't be any danger from carbon monoxide leakage, no more than we have with the garage door leading into the laundry room.

I was unfamiliar with the expression "bump-out," but looked it up just now -- "an extension of a room or building that creates a projection in a wall: e.g., "a rear bump-out provided an ample extension to the master bedroom."

I'm impressed with how much you care about your kitty cat, and it sounds like you have a really cool plan.

I hope if you do this, you'll come back and post pics!!!! It's what I've been wanting to do, too. I wish I'd had it done when we built the house 2 yrs ago, but the only fore-thinking I did was have the builder put a header between 2 studs and make sure he didn't run any wires in the space on the wall in the small mudroom where we'd do this.

Like you, I was envisioning a bump-out into the garage that would be fully insulated and have an exterior "door" (sealed, etc., to meet code) for litter box access. For now, our 2 boxes are under the mudroom bench, and I hate them being there.

Thanks, petaloid. We are quite fond of him (silly old thing). ;-)

Tracey, I will come back and post pics but it won't be any time soon. Hubby is working long, long hours, including weekends, right now (poor guy) so the earliest opportunity we'll have to build this will be late March.