Awful smell from (gable) wall cavity - dead bird?

spinal_tap

Registered User
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125
Just after moving into a house. Was built for a year or two and there was never an external vent cover put on the upstairs ensuite, so it attracted birds. The vent was cleared last week, but now there is a smell from it.
There was an awful smell in the ensuite, so I removed the vent (internal side) and a length of plastic piping which serves as the vent funnel. The smell is definitely coming from the wall cavity (it’s an external brick wall, gap, sheet aerobord, internal brick wall), so I think there’s possibly a dead bird down there.
What I need to know is how to get rid of the smell and prevent maggots, flies etc., but in doing a quick bit of research on the Net, there are also suggestions that it could be a build up of water (remember, this was an exposed second-storey hole on a gable wall) and this is a mould smell. Smells like rotten meat to me though.
Suggestions, help, assistance?
Thanks