First off, I don't want to evict them unless I have to. And I already plan on littering the garden with bird boxes and feeders (I've just moved in).
I don't think it's an overflow because the house still has a downstairs bathroom and I don't think it's ever had one upstairs. But I have no idea how to determine if they're damaging the house. I think the hole lines up with a lath and plaster partition wall so it's possible that they've got a 12-bed mansion back there.
If it needs fixing I'd happily replace the brick with a special nesting brick.
Almost guaranteed they will have masses of nesting material in some sort of cavity. I doubt there will be any damage though.
Might the hole be an overflow for water tanks in the loft? I've seen recently people piping the overflow into the vent stack. Or it might just be a cavity vent that failed?
First off, I don't want to evict them unless I have to. And I already plan on littering the garden with bird boxes and feeders (I've just moved in).
I don't think it's an overflow because the house still has a downstairs bathroom and I don't think it's ever had one upstairs. But I have no idea how to determine if they're damaging the house. I think the hole lines up with a lath and plaster partition wall so it's possible that they've got a 12-bed mansion back there.
If it needs fixing I'd happily replace the brick with a special nesting brick.