Q. My son and his family just moved into a brand new condo in a high rise building and the building has rats! Fortunately not in their condo, but my son saw a rat in the trash room and one of their neighbors actually did have one inside their condo. The manager says it’s the builder’s fault. He says that rats were actually built into the building during construction. Is that possible?

A. I’m sorry to say it is possible, and not that uncommon. It’s easy for rats to enter a building during construction, or even during renovation. Walls and other openings are left open for months, both inside the building and to the outside. Construction materials provide hiding places and nest sites for rats. Construction workers leave lunch leftovers that attract rats. During construction, one floor of a high rise building is normally taken over by the construction crew for material storage and work areas. Construction workers leave half-eaten hamburgers, pizza, and other high energy foods. This floor is often the heart of the rat infestation.

During the early stages of construction, the building can become a haven for large numbers of rats, with easy entry, access throughout the building, and plenty of food and harborage. But at some point, this ideal habitat changes. The outer walls are closed and new windows installed. The rats become trapped inside. Floor by floor, interior partition walls and doors are added, utility lines completed, and the building sealed off into distinct areas. At this point, the rats are probably sealed into the wall voids. Here, they can travel from room to room, and floor to floor.

The rats’ food supply declines too as the construction crew is reduced and parts of the building are cleaned up for occupancy. Foraging rats suddenly become very visible to new and potential tenants (and, of course, to the building’s manager). Unfortunately, rats introduced during building construction can remain a problem for years.

The time to have dealt with this rat problem was before construction even began. The contractor should have surveyed the building site for rodent activity and should have had a pest control company rid the area of rodents. Further, there should have been a plan to intercept any rodents trying to move in, and rodent control should have been ongoing inside the building as it went up. Control of rats trapped inside would have been easier before the building was occupied. Now, building management will now have to rely on the skills of a pest control company to eliminate the rats with the least amount of visibility and disruption to tenants.