Angela wrote:
2. The actual door seems to be on the inside leaving the tunnel exposed to
the elements (or have I got that wrong?). What's stopping it filling with
rain and allowing water to seep into the cavity wall?

If the tunnel has even a very slight slope it would only fill with water
when you are being flooded.

(Only partly tongue in cheek do I ask this!) I assume that if the
catflap has any transparent area it requires Fensa registration or
building control approval? And do the catflaps themselves need to have
any approval (BBA?, BS/EN?)?

--
Rod

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