How to Guide on Insulating Your Cat Flap

Updated on November 30, 2016
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I strive to balance aesthetics, functionality, and quality with costs when planning DIY projects in the home and garden.

Bespoke Insulator bolted in place over cat flap.
Bespoke Insulator bolted in place over cat flap.

The Sufferance of Cat and Dog Owners

If you own a cat or dog and you provide them with their own pet flap, then over the winter months you are going to suffer the discomfort of draughts; which invariably means more expensive fuel bills as you turn up the central heating to compensate.

There’s nothing we can do about it during the day because our cats need access; but in the evening (once our cats are in for the night) we can shut the cat flap. This then helps to reduce the draughts and heat loss a little; albeit it can still be draughty, especially on a cold wintery windy night.

Most cat flaps have a magnetic seal so they’re not so bad, even when in use; although they still let in some draughts, and are a source of some heat loss. However, because we have a Maine Coon cat, he’s too big to fit through a standard cat flap, so we’ve had to install a small dog flap for him. Maine Coons are large cats, typically weighing between 15 lbs and 25 lbs; ours (Greebo) weighs 17 lbs.

Irritatingly, dog flaps don’t usually have the magnetic seals common in cat flaps, so they tend to flap in the wind; and although with ours we can pull down the plastic shutter that comes with it, when we close it for the night, noticeable amounts of cold and draughts still get in.

Click thumbnail to view full-size
Cat flap in open position, which offers little protection from cold winds.Cat flap closed, with plastic cover down; which offers no protection against draughts.
Cat flap in open position, which offers little protection from cold winds.
Cat flap in open position, which offers little protection from cold winds.
Cat flap closed, with plastic cover down; which offers no protection against draughts.
Cat flap closed, with plastic cover down; which offers no protection against draughts.

Introducing Our Pet Subject

Greebo and Dippy (his sister) are our two adorable and lovable cats. Their father (who Greebo takes after) is a Maine Coon, and their mother (who Dippy takes after) is a Rag Doll; another large breed cat.

Maine Coons are often described as ‘gentle giants’, reflecting their passive nature; and are amongst one of the more intelligent breed of domestic cats. Not only are they as large as small dogs but they also have many characteristics which are more dog than cat like.

For example, Greebo depends on human companionship and will sit and interact with me on an evening, and demand my attention during the day when I’m gardening or doing DIY in my workshop. He quickly learnt the command for sit (with little training) and unlike any other cats we’ve owned both Greebo and Dippy come when called; which makes it easy to get them in on an evening. Albeit they sometimes like to play ‘catch me if you can’ or ‘hide and seek’ with us in the back garden; before finally conceding to our demands and come in.

Our Maine Coon, big as a small dog; with wine bottle in foreground as size comparison.
Our Maine Coon, big as a small dog; with wine bottle in foreground as size comparison.

Finding the Right Solution

Something Simple yet Effective

When our cats are in for the night we can close the cat flap, and previously over the cold winter months we would push a large cushion against it to act as a draught excluder. Although of limited benefit, it wasn’t as effective as I would have hoped in that I could still feel draughts around the edges of the cushion.

Therefore, in the absence of anything suitable and affordable on the market, I decided I would make my own bespoke cat flap insulator that could at least be used over night; once the cats were in.

What I needed to make was a rigid padded board that I could press tightly against the cat flap, and lock in position, to seal all gaps and prevent draughts; and which would also provide some insulation to keep the warmth in.

The Freedom to Roam

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Multipurpose

Alternate Use When Not Insulating the Cat Flap

While relaxing over a cup of coffee (my equivalent to a thinking cap) I pondered on what to do with the Insulator board when not in use e.g. during the day and in the summer months. I wouldn’t really want it to clutter up the conservatory, be in the way or take up valuable storage space.

That’s when I had my moment of inspiration that if it was laid flat on the floor, with the padded surface facing upwards it would automatically make a superb cat bed.

The only issue to resolve was to how to get it to lay flat without the bolt getting in the way. With a little thought, the answer seemed obvious. Put feet on it that are bigger than the thickness of the bolt; with the feet doubling up as pull handles when pushing the insulator board against the cat flap on a night, or removing it in the morning to let the cats out.

This article is about my solution to what is undoubtedly a common problem for cat and dog owners; with a design that also makes it multifunctional, so when not in use to insulate the cat flap it also doubles up as a cat bed.

Outline Design and Function

Having the concept in mind, I made another cup of coffee and while sipping it sketched a simple design, as follows:-

  • Half inch of foam firmly held in place by carpet upholstered to a sturdy piece of plywood; to act as the padded surface that could be pressed firmly against the cat flap, with
  • Two rail handles and a bolt fitted on the back.

I could have used upholstery material, but opted for carpet because the thickness of the pile would act as a natural draught excluder; especially as I would be using a piece of Axminster carpet off-cut, leftover from when we recently had our livening room re-carpeted. With Axminster being a particularly good choice for this purpose because of the density of its pile, albeit any carpet with a dense pile would be ideal.

  • The bolt on the back ensures that when the cushioned board is pressed hard against the cat flap it can be locked in position; ensuring a tight fit to keep out the draughts.
  • The rail handles, used to push or grab hold of and pull when placing the cat flap insulation board in place or removing it, also acts as feet and Keeps the bolt off the floor when the insulator board is alternately used as a cat bed.

This Is What a Cat Flap Should Be Like

Below is a short video of a fully insulated pet flap; and about time too. It’s the only one I’ve been able to find so far that's truly insulated; just like a front door or double glazed window.

However, with its level of sophistication and technology it’s currently far too expensive for most pet owners to be able to afford.

PetWALK Fully Insulated Cat Flap

Construction

The few bits of materials needed don’t cost much, and as it’s such a simple design its easy and quick to make, taking no more than an hour.

As it happened it didn’t cost me anything, apart from the cost of a bolt, as I had all the materials I needed in my workshop; including the carpet, which was an off cut from when we recently had our living room re-carpeted.

The board, on which the foam and carpet are fitted, should ideally be at least half an inch thick. I would normally have used plywood but I had a spare piece of pine board in my workshop (which is just as suitable), so I opted to use that.

The steps required to construct and assemble the insulator board for a pet flap are as follows:-

  1. Measure for the size of the required board, for the height from the floor, adding on a few inches above the top of the cat flap; and for the width (space permitting) adding at least a few inches to each side of the cat flap.
  2. Cut a piece of thick plywood slightly smaller than the required size; to take account of the thickness and density of the carpet’s pile. The plywood should be at least half an inch thick; although 3/4 inch plywood will be better as you’ll be able to use slightly longer screws, making the construction stronger.
  3. Cut a piece of 1/4 inch plywood slightly smaller than the other piece. This second piece will cover the edges of the carpet on the back (giving a neat finish) and provide a flat surface for fitting the rail handles and bolt. This piece needs to be slightly smaller especially at the bottom so that it doesn’t scrape along the floor when used for insulating the cat flap.
  4. Round and Smooth the edges of both pieces of plywood with an electric sander.
  5. Cut a piece of half inch foam to the same size as the first piece of plywood.
  6. Cut the carpet a couple of inches larger all round to the dimensions of the main plywood.
  7. Cut a couple of pieces of timber to size (a few inches shorter than the height of the cat flap insulator), to act as rail handles which you can pull and push when positioning the insulator in place or removing it. For added grip you may wish to fashion the hand rails on a lathe or with a router.
  8. Measure and Pre-cut timber for holding the cat flap insulator in place on one side, and if necessary for somewhere to bolt it in place on the other side; see the illustrations below as an example.

Click thumbnail to view full-size
Sheets of plywood used to make cat flap insulator.Scrap wood used for making slot for cat flap insulator to fit into.
Sheets of plywood used to make cat flap insulator.
Sheets of plywood used to make cat flap insulator.
Scrap wood used for making slot for cat flap insulator to fit into.
Scrap wood used for making slot for cat flap insulator to fit into.

Assembly

Assembly is done in a few simple steps that shouldn’t take long, as follows:-

  1. Place the foam on the thicker plywood.
  2. Lay the carpet over the foam.
  3. Turn the whole lot over.
  4. Fold the carpet over on one end, and tack it in place with a few staples.
  5. Pull the carpet taut at the other end, fold it over and tack in place.
  6. Tuck-in one of the carpet corners and tack in place; you may need to trim off some of the carpet at the corners because of its thickness.
  7. Repeat for the other three corners.
  8. Fold over and tack one side of the carpet in place.
  9. Pull the other side taut as you tack it in place.
  10. Finally, tack firmly in place all round, with staples about every half inch.
  11. Screw the thin piece of plywood in place on the back.
  12. Screw the rail handles and bolt in place on the back.

Click thumbnail to view full-size
Carpet being stapled in position over foam and plywood to create cat flap insulator.Thin sheet of plywood screwed to back of cat flap insulator.Plywood padded with foam and upholstered to carpet to create cat flap insulator.Back of cat flap insulator with pull handles and bolt fitted.
Carpet being stapled in position over foam and plywood to create cat flap insulator.
Carpet being stapled in position over foam and plywood to create cat flap insulator.
Thin sheet of plywood screwed to back of cat flap insulator.
Thin sheet of plywood screwed to back of cat flap insulator.
Plywood padded with foam and upholstered to carpet to create cat flap insulator.
Plywood padded with foam and upholstered to carpet to create cat flap insulator.
Back of cat flap insulator with pull handles and bolt fitted.
Back of cat flap insulator with pull handles and bolt fitted.

Snuggly Fits Skirting Boards

The beauty of the design is that because the foam is under more tension (and therefore more compressed) at the edges, it gives the insulator board a natural curve that conveniently fits over the skirting board; giving a nice snug fit over the cat flap.

Fitting

The cat flap insulator is held firmly in place on one side by slotting into a recess created by screwing two pieces of wood together (one wider than the other); and screwing that to the wall or door.

The cat flap insulator is then bolted in place on the other side; which may require fitting a piece of timber to the wall or door that’s the same thickness as the insulator when it’s in its compressed state e.g. to ensure a tight fit to prevent draughts.

Likewise, to prevent draughts, the insulator should be a tight fit in the groove. If it’s just a loose fit then you’ll still get the draughts (cold airflow) around the edges of the insulator.

So the initial fit, to get the correct width for the wooden groove and correct position for the bolt may be trial. Therefore I would recommend initially trial fitting the groove assembly to the wall or door with just a couple of screws. Then slotting the insulator in place and pressing hard on it to see how well it fits. This should give you some idea on what adjustments you may need to make to the groove assembly.

Once you’re happy with the groove assembly (with the bolt fitted to the back of the insulator), press the insulator firmly in place over the cat flap and either mark or measure where it’s going to bolt so that you can fit it into place.

Click thumbnail to view full-size
Insulator board bolted in position over the cat flap.Insulator board doubling up as cat bed when not required for the cat flap.
Insulator board bolted in position over the cat flap.
Insulator board bolted in position over the cat flap.
Insulator board doubling up as cat bed when not required for the cat flap.
Insulator board doubling up as cat bed when not required for the cat flap.

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