Insect Mesh

[spacechimp]

I am planning to install an external vent for an extractor fan, but it will be above my neighbour's roof, meaning I want to get it right first time, as I won't be able to access it. What are the largest holes I can get away with if I am to prevent any unwelcome visitors? Should I worry about insects laying eggs through holes they cannot themselves fit through?

[The Builder]

I'm afraid I don't know actual hole sizes. It's usually just referred to as "insect mesh".

Assuming it's a standard 100mm duct with a 153 x 153 mm grill ........ just use one of these........

http://www.ebay.co.uk/itm/4-100mm-Fixed-Outlet-Inlet-Grille-Insect-Mesh-Extractor-Fans-Flexible-Ducting-/111030880953

[spacechimp]

Already have one of those (though with louvres). I've gone with 2mm apertures in the mesh.