VERTEBRATE PESTS: Ceiling Voids And Pest Issues

April 12, 2002

Inside most buildings, ceilings are prone to invasion by a range of animal (and insect) pests. In fact, ceiling spaces serve as ideal artificial environments for pests — especially cryptobiotic pests, such as mice, roof rats, bats, squirrels, cockroaches and carpenter ants. There are several reasons for this.

First, our ceiling voids provide pests with excellent concealment and protection. Ceilings are enclosed, usually dark, and not easily accessed. Too, they are above the perspective of people and the pest’s other predators.

Second, ceiling voids are often warm areas due to the rising heat from the floor below. Warmth is a critical resource for most small mammals.

Third, ceilings often contain many utility lines that pests can use to quickly and quietly travel from one room to another or from one floor to another.
And fourth, the typical distance from a ceiling to a floor (8 to 10 feet) is easily within the daily foraging ranges of all rodents and most insect pests, allowing them quick and easy access to food areas.

Consequently, office buildings, schools, restaurants, nursing homes, child-care facilities, hospitals, commercial hotel kitchens and similar commercial accounts are vulnerable to pest infestations in ceiling spaces. In fact, there is no shortage of field case histories of persistent callbacks being attributed to ceiling infestations. Yet, during routine preventive service visits to commercial buildings under “general pest control” contracts (e.g., mice, ants, cockroaches, etc.), the ceilings are often overlooked as a necessary part of the service.

THE REASON. For any pest professional that has run a route, the reasons for this are obvious. Ceilings can eat clock. Stepladders are needed, and popping ceiling panels and getting them to quickly reseat can be a hassle. Too, many technicians are not sure which panels to check. Some technicians claim that when they do check ceilings, they don’t see anything, and eventually stop checking all ceilings altogether except for complaint cases. This all culminates in reasoning that if a pest problem develops in a ceiling, the client will call, and it can be addressed at that time.

But inside commercial buildings, suspended ceilings should be serviced on a pro-active, not reactive, basis. Considering how fast pest populations can proliferate in these ideal protective spaces, infestations can easily grow from a few animals to a serious level, requiring an extensive amount of work.

Recently, for example, a middle school in an affluent community had repeatedly complained to their pest professional of mouse droppings on desks and on the floors of the classrooms. The technician in this account diligently placed traps inside floor level cabinets and closets and other spaces out of the reach and attention of the children. Because the school principal was concerned about all the mice, a teacher was also assigned to follow the service technician around on “his rounds” to make sure he was “being thorough” on his service visit. Because he was catching the occasional mouse in the closets and cabinets, both the school personnel and the technician assumed the mice were “floor level” mice. Over the course of six months the technician never did check the ceilings.

New mouse captures from time to time were assumed to be coming in from the outside. But once a few ceiling tiles were checked, the abundance of mouse droppings and the smell of urine confirmed the source of the problem to both the school personnel and the red-faced pest technician. Unfortunately, this technician was merely harvesting off mice from a much larger population existing in the ceiling spaces throughout several areas of the school.

This real-world case is representative of pest infestations and callbacks in commercial buildings. In fact, it is uncommon to not find some evidence of rodents that used the ceilings of many commercial buildings. Moreover, in buildings that have had sustained prolonged mouse infestations, maintenance personnel often joke about the “turd showers” they receive when they pop a ceiling tile or overhead panel and are rained upon by rodent droppings (or abandoned packets of rodenticide baits).

Technicians should acknowledge (and be properly trained) that commercial building ceiling voids are “pest-vulnerable areas” that must be subjected to inspections, monitoring efforts and possible treatments using traps and/or baits on a periodical basis.

TIPS FROM THE FIELD. But, how should ceiling voids be serviced on a routine basis? And which voids should be checked? Here are a few recommendations and field tips.

1. Not all ceiling voids and not all areas of ceiling voids are equally prone to pest invasions. Ceilings of commercial kitchens and associated food-storage rooms are especially prone to pest activity for the reasons discussed above. Plenum spaces that contain high airflow or cool air currents are less attractive to pests.
2. It is not necessary to check every ceiling panel (nor is it practical to try). Sources of warmth can be used as indicators as to which ceiling panels to pop. As mentioned previously, heat is an important resource to pests. Thus, those panels located above appliances and areas generating heat are excellent ceiling areas to check, such as areas above dishwashers, stoves, refrigerators, coffee stations, vending machines and so forth. Areas where warmth and food sources coincide are especially important to be checked.
3. In the absence of obvious heat sources, those panels located in the ceiling corners and a few perimeter panels can be checked.
4. Ceiling panels where vertical utility lines (electrical conduit, plumbing lines, cables, etc.) enter through the ceiling should be checked.
5. Inside the ceiling voids, light leaks from any exterior line or utility penetrations should be noted. Clients should be informed of such openings and the importance of having them sealed properly to exclude pests from secretly entering the building on a regular basis.
6. Obviously stepladders are necessary equipment. But it may not be practical for some professionals to lug a ladder around from one commercial building to another for some inner-city routes. For large skyscrapers, office complexes and similar types of routes, ladders may need to be kept on the premises and designated for pest management services.
7. Ceilings can be monitored for mice and other pests using snap traps, secured glueboards, Detex Blox installed into RTU stations, or attached to fishing line or via some other means.
8. Ceiling tiles should always be lifted slowly and carefully to prevent any rodent droppings from falling down on any desks, counter tops, appliances or personnel.
9. Reseating popped ceiling tiles can be annoying and time consuming without the use of the proper tool. A carpet tack remover (about $5) can seat tiles back in place quickly and easily. This tool also has a dozen other uses in everyday pest management work.
10. The frequency of ceiling inspections will vary significantly. This might mean weekly, monthly or quarterly. The frequency depends on the past history and specifics of the account.
11. Clients should be informed as to the need to remove any rodent excrement so that building employees are not subjected to any possible animal feces/urine residues.
12. Rodenticide baits should never be tossed into ceilings and then “abandoned” in efforts to eliminate hard-to-reach rodents (see “Abandoned Baits in Buildings,” PCT, July 1998).
13. Finally, but perhaps most important, commercial sales professionals should incorporate into price bids the time necessary for technicians to be able to inspect the ceilings periodically. And this should be explained to the client (as to why, perhaps, your bid is slightly higher than the competition).

CONCLUSION. There is no doubt that popping and replacing ceiling tiles is more time consuming than performing routine inspections of floor areas and shining a light under the kitchen sink and water heaters. But given the frequency that rodents and insects infiltrate overhead spaces, not servicing these areas regularly leaves the account prone to annoying and costly callbacks — and dissatisfied clients.

The author is president of RMC Pest Management Consulting and can be reached at or 765/939-2829.