How to Build an Almost Indestructible DIY Dog Door

How to make your own almost indestructible doggie door. It was over a decade ago now (aw to be 23 again) when I finally, totally and completely, lost my mind with the expensive, absolute junk, doggie doors that are on the market. We live in northern MN and we generally went through two of the the most expensive doggie doors every winter. That’s nearly $400 a winter because our winters get so cold the plastic those doors were made of would literally just shatter. We had three 100 pound dogs at the time and I was at my wit’s end. I just could NOT believe there wasn’t another option out there so, obviously, I set out to make my own.

I went to my local fleet store with only a rough idea of how I was going to do it. I knew I planned on copying the basic doggie door design with an outside magnetic frame that sticks to the outside of the door and covers the seam of an inside flap. My biggest problem was: “What the heck am I going to make it out of!?” They sold outdoor rubber/mat/rug material by the foot but it was pretty darned thin and I was only half convinced it would hold up for very long. (Of course, if I had found nothing else, that was going to be what I used to make the doggie door out of regardless.) Rubber rugs was what I looked at first but the options were expensive and not at all ideal.

I really needed something that didn’t have any designs and stuff on it. Then I wandered into the auto parts area and stopped dead in my tracks. Mud flaps. Big, heavy duty, rectangle, very durable, rubber mud flaps. The lightbulb flashed above my head and I grabbed two sets of the biggest rectangle ones I could find. From there I also purchased magnetic strips by the roll and, let me tell you, they’re not ideal (I need to find a better alternative) but its all my fleet store has available so here we are.

(The reason they’re not ideal: because they come in a roll they curl which means they’re a pain in the butt to keep in place while the glue is drying…) You can see I did this the same weekend we replaced a window with a new exterior back door in the workshop.

The size of the mud flaps I’ve always purchased for this is 18×24 (they’re actually called “mud guards” here they are on Amazon) so I’ve always made the doggie door as big as possible according to the flaps. Which is a 15×20 inch hole cut in the door.

(My 140 pound Mastiff had no problem using this size doggie door so I can’t imagine what kind of bear that’s living with you if you need it to be bigger lol! I’ve found what really matters is to make sure its HIGH enough on the door so your dog doesn’t have to duck to get through it. They have an easier time stepping over something than ducking under something.)

In this tutorial I’m doing a double flap doggie door which will be a frame and inside flap on BOTH sides of the door.

I headed out to the garage and made my cuts out on the concrete floor. I’ve always used a utility knife for this but a really robust pair of scissors MIGHT work. I find scoring it a couple of times works best before trying to cut all the way through it. First I cut out the two interior flaps at 20×15. These MUST be cut small enough to hang (and swing) freely inside the opening of the door. Notice how I kept the entire reinforced top of the mud flap in tact. Next I needed to cut the center out of my frames.

I measured the center square smaller than the interior flaps I already cut. So I cut both of my frames out at 13×19 so they will over lap/cover the seam between the opening in the door and the interior flaps. With my pieces now cut out I was ready to add my magnets to the exterior frames.

Again, I kind of hate these rolls of magnets but I made do with liquid nails and a lot of coffee cups to weigh them down until the glue dried lol. I haven’t found a magnet yet that has a sticky enough backing to actually do this doggie door job properly. Liquid nails, gorilla glue etc. works just fine.

We just put in a new steel exterior door in the workshop that we cut using an angle grinder so the magnets work perfectly but if you’re using a wood door you will need to add steel of some kind for the magnets to grab on to. After a couple of hours of dry time in the kitchen it was time to install. We attached a frame and an interior flap both on the outside and inside of the door. Interior flap first, making sure it hangs/swings freely, and then the frame over that using steel screws through the tops of each, utilizing the heavy duty top of the mud flap. (A second set of hands here is VERY helpful.)

Done and done!

Annie has no problem using it as the mud flaps are pretty darned flexible. This is the first time I put an interior flap on both sides but I wouldn’t do it with just one interior flap again.

(Most commercial doggie doors sit inside of the door opening with a single flap that hangs in the center and an outside frame on either side.)

Annie goes through the inside of the opening of the first frame, pushes with her nose out through the interior flaps, which lifts the outside frame as she goes. Once she’s through it all slaps closed and the magnets hold it all down on both sides, sealing it up from wind really well. When I first made this, with three 100 pound dogs, it still took nearly two YEARS before I had to replace any part of this doggie door design and that was only the interior flap that finally ripped on one side. I’ve had people mention that this can’t possibly be that great for keeping out a -20 degree Minnesota winter.

Of course not. But this doggie door does just as well as all the other crappy doggie doors on the market and costs less than $100 to make. Even with constant use, in any kind of weather, this doggie door will last for YEARS. And you could totally have some fun with this as there are TONS of designs out there on mud flaps that you could use for the interior flap! I’m pretty sure you can even get custom mud flaps made lol.

This was one of my proudest DIY achievements!