Insulating a catflap or similar

August 12th, 2012 by J-P Leave a reply »

What do you do once you’ve picked the low-hanging fruit of sustainable household improvement? Let’s say that (like us) you’ve already had your loft and cavity walls insulated, and all your windows are double-glazed. Where do you go next? The two main directions are: think big (replacement boiler or wood burner, triple glazing, solar water heating); or think small (changing habits, draught exclusion.)

Tomorrow and Tuesday we’re thinking big – we’re getting our 30-year-old, X-rated boiler replaced with an A-rated combi – so this weekend I decided to think small. I’ve found taking part in the recent Carbon Conversations very inspiring but also full of practical advice; as a result of some of the discussions we’ve had together, I had a list of quick fixes I could make to improve draught exclusion. First I fitted a draught-excluding brush on the letterbox; then I glued an escutcheon on our existing back-door mortise lock, to block the piping gales which tend to whistle through the keyhole every winter.

All of these small changes meant we could avoid thinking the biggest little problem we have these days: the catflap. When we moved into this house three years ago, it had a catflap, but we had no cat. The simplest solution was to gaffa-tape it shut, with an old teatowel squeezed in behind the tape, to provide basic insulation and prevent draughts.

However, now we have a cat. Since we untaped the catflap, we find that it flaps itself under the slightest provocation: a door opened or closed upstairs, or a strong breeze in the back garden. When we added to that the fact that the cat has worked out how to open the catflap when we’re not around (the flap is quite old and has only three modes, none of which are fully locked), we finally had to admit: something had to be done.

The first thought is of course to get a new catflap. But that will probably involve a new lower door panel, given the mess the previous owners made of installing this one, which will mean decisions about maybe a new door… And as we’re currently anticipating a half-week of home-improvement hassle from the boiler replacement, we wanted something that definitely works: even a new catflap could have insulation problems, when you’re looking to really insulate your house. Also, it’s best to try to improve existing purchases than make new ones, wherever feasible.

So here’s what I built:

Image of the catflap hat/cover opened

“A catflap on a catflap”, you might cry: and you’d be technically correct; but, given the caveats I mention above, I prefer to call it a hatch or cover. This way we’ve been able to construct this to our own preference for strong insulation: hopefully we’ve ended up with something that might not be draughtproof, but is certainly close enough to it. And we can always replace the hatch with better materials later if need be.

Still, although I’m not a DIY expert at all – I’d say this is my neatest job so far, and it’s hardly carpenter standard – this was nonetheless a straightforward and cheap project, once I’d got the right tools for the job. If you want to do something like this yourself – maybe you’ve not got a cat, but you do have a small and draughty window that you’d like to seal up with an hour’s work – then here’s some pointers.

  • The hatch itself was made from an offcut of wood; after sawing it to be slightly smaller than the area of the catflap, but plus a few centimetres, I attached those few centimetres with a butt hinge (one where the hinge joint lies relatively flat when closed) to the bottom siller of the door, where the wood was thickest.
  • The offcut has a slight bevel to it, which means that when the hatch lies open, the edge of the hatch doesn’t butt up against the siller: otherwise, the hatch would probably only open 90 degrees before straining. This does also mean that the screws end up poking out through the bevel slightly. A professional finish would see them filed down and the bevel repainted.
  • I bought a new multi-purpose saw (55cm) for the purpose, and a mitre square to score a straight line at a right angle to the existing wood edges with a craft knife. Honestly, these were the two best purchases in terms of the ease of doing the job. You know what they say: a bad workman gets better tools, or something like that. It really helped me.
  • I put Stormguard EPDM rubber strips around both the existing catflap frame and the new hatch. The hatch is secured when closed with a cabin hook, which is probably the weakest point in the whole design. A tighter closure method would make the draughtproofing that bit better, as there is still a slight gap in theory if you pull the hatch hard against the cabin hook.
  • The two holes in the wood are a result of it being an offcut. I’ll probably fill them with “fake wood” filler or rubber sealant next time we get a tube of it for household repair; or just white tack in the mean time.

The total cost, not including the new tools which I hope to get plenty of use out of, was: £5.50 for the cabin hook, £3.30 for two butt hinges, and around £1 for the lengths of EPDM strip cut from an existing roll. So less than ten pounds, plus around an hour to an hour and a half’s work.

The hatch has already stopped the flap under it from moving, whenever doors are opened elsewhere in the house; so there’s been an immediate effect in terms of draught improvement. To be certain, we’ll have to wait until later in the year: that’s when the offer of thermal imaging photography for Witney residents will hopefully determine once and for all whether or not the catflap is still causing insulation problems that need urgent treatment.

Anyway, this work hopefully means that our kitchen now keeps more heat in. It’s certainly stopped the cat from sneaking out.

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