Spiders have to eat, just like everyone else. If there's no food, they'll look elsewhere. In otherwords, there may be a bug problem in the building, either above or below ground that is providing food for the spiders. Also, some spiders like moisture. Be sure there are no leaky pipes anywhere, including laundry hoses, etc. Check and fill with caulking or insulation, places like around water pipe holes, laundry room pipes, holes in screens, etc. If the furnace ductwork isn't tight below the building, spiders may be crawling up thru the ductwork into your floor registers. Require that your maintenance people check the basement areas for places they can get in. Worse case, they could pay you (or you pay) to stay in a motel for 1-2 days (with your pets) while they spray, however, if the source of the problem isn't found it will be a matter of time before they come back. I'm petrified of spiders, myself.