Noises in Your Roof? 

I get questioned occasionally about how to tell what it is that is making a scratching noise in a roof. "Is it rats, mice or birds........or elephants?"

If you are hearing scratching or gnawing sounds in your roof void it is unlikely to be elephants (well, not fully grown ones) but whatever it is can sound 'pretty big.' Ceilings amplify sound like the sounding boards of musical instruments. And if the noises are heard at night when there is little other sounds our ears are more sensitive and amplify the noise in our minds.
A good guide to deciding whether the noise is caused by birds, rodents or other animals is the timing of the noises. If you are hearing the noise predominantly in the middle of the night, you almost certainly are sharing your home with rats or mice. If the noises are only occurring during the day or at dusk and dawn check around the eaves for birds entering and leaving.

OK. So you are hearing the noises in the middle of the night. Is it rats or mice? Rats are larger and do make louder noise but that is little help if you have nothing to compare with. Listen instead for the frequency of the scurrying feet. Mice make a sound where their paw sounds follow each other so quickly it is very difficult to separate them, so the sound is almost continuous. The sound of rats running displays a more definite sound of their individual paws.

Rats and mice have incisor teeth (front two teeth of each jaw) that are large and continually growing. The teeth have hard enamel on the front surface and softer dentine behind. As rats and mice gnaw they wear the teeth down and sharpen them into chisel-like implements through uneven wearing. Rats and mice gnaw things other than food to keep their teeth worn down and sharp. Unfortunately for us they often choose to gnaw wiring, plumbing, joists and items stored where they are.

If rats and mice regularly use a hole or gap to pass through they will gnaw around the gap to open it up and make it easier to enter or exit. They will gnaw wood, plastic, metal and even concrete if they need to. The sound of rats or mice gnawing can be distinguished by the rate of biting. Mice gnaw at about 4-5 per second, rats 1-3 per second.

A simpler way of determining which rodents you have in your roof is to enter the void (if possible) and look for evidence in the form of droppings. Mice produce small black-grey droppings approximately the size of a large grain of rice. Rat droppings are much larger, 1-2cm long.

In New Zealand, the other animal that can be a cause of noises in the roof is the possum (Australian Brushtail Possum). This is a much larger animal than a rat or bird and it usually easy to tell its presence from the much heavier and slower footfalls and they don't gnaw wood like the rodents will.

Other causes of sounds in a roof can be tree branches rubbing on the roof or eaves; usually heard only when the wind is blowing, or expansion and contraction of timbers and gutters as the roof warms up during the day or cools down at night.

David Brittain
Kiwicare