Pets are generally ok because the floors in all our apartments and houses have wood and tile floors, rather than carpeting.

However, cats consistently damage apartments and houses by sitting on window ledges and either
(1) leaning or scratching themselves against the window screens, or
(2) scratching on the window screeens.
So any apartments or house where cats can stay will eventually have several screens torn or popped out.    A given cat may only weaken one or more screens without physically damaging them.     A subsequent tenant's cat might actually tear or pop the screen.

Hence we charge $8/cat/mo which equals $96/cat/yr

There is no extra charge for dogs or pets which live in cages or tanks.