Best DIY Methods for Cockroach and Bed Bug Control in Older Buildings

Filling those gaps with aluminum foil is a solid option, especially since it's reversible for renters. You could also try using spray foam designed to block insects, but be careful—it expands quite a bit and can make a mess!

Mixing powdered borax with some sugar (50/50) is a great way to deal with cockroaches. Just place it in a dish, clearly labeled, out of reach of pets and kids. Roaches will eat the sugar and spread the borax to others, which can suffocate them. Spraying the mix into cracks is also really effective!

You could use Advion Roach gel along your baseboards for the roaches, and for bed bugs, I've heard fire works well (though maybe not the safest option!).

Diatomaceous Earth works well, plus consider using caulk or insulation foam with some backer rods for larger gaps. For any really big gaps, like the size of a nickel, shove in some steel wool first to keep rodents out. Also, for bed bugs, you might want to think about calling a professional—it's a serious issue!