This summer we found cockroaches regularly appearing in our kitchen and always on our benchtop where our cooktop is located .
We initially thought they were coming in from under our island bench where the water pipes come out of the slab, but couldn't figure out why they appeared on & in our cupboards across the way.
Until............. I saw one hanging off the underside of our rangehood!!! It promptly fell off directly onto the benchop & scuttled away with me carrying on trying to kill it.
Aha!!!! Mystery solved
As we have a window on the wall between our cooktop & r/hood, I figured that the buggers were attracted to the kitchen light at night, crawled onto the brick wall & found an entry through the grill on the outside wall of the house!!
We have since added mesh under the grill & NO MORE ROACHES !! Yay
Since our d/stairs bathroom extractor fan also has an outside vent, we will be meshing that one also - just in case.