Want to avoid costly fines from the city for renting out illegally subdivided apartments? It's easy — just don't open the door. In the aftermath of a fatal fire that killed three Bangladeshi immigrants in an illegal basement apartment without sufficient exits, the Daily News pulls up some damning figures on the city's inability to crack down on these surprisingly ubiquitous deathtraps.

Each year, the city receives 20,000 complaints about illegal apartments, but it closes half of those cases without ever stepping foot inside the buildings. That's because building owners can avoid inspections — and fines — by simply not answering the doors when inspectors knock. If city inspectors can't get into a building after two visits, they close the case until they receive a new complaint.

The paper details a suspected brothel and illegal apartment building on 18 Ave. in Brooklyn that inspectors have visited 22 times without gaining access, as well as a purportedly illegal day care center with no fire exits on Ash Ave. in Flushing that they have visited repeatedly over the past nine years without getting in.

It seems that the landlords who rent out illegal apartments already know the about the closed-door policy, because the rate with which inspectors have gained access to such apartments has fallen from 60 percent in 2006 to about 50 percent in the last three years. And about that illegally partitioned Woodside building where three men died last week — the owner was fined $800 for illegally dividing apartments in 1998, but records show he never proved that the illegal apartments were made compliant.