We also wire them with the light switch but also install a humidistat w/ timer in parallel ... that way if the tenants shuts the lights out when leaving the bathroom after a steam shower, the fan remains running for 20-30 minutes or until the humidity falls below the preset threshold.

Watch for mold and humidity, also more tricky to figure out and resolve.

We use a variety of thermostats (Honeywell, Nest, Homewerks, ecobee) with our building monitoring / management system, but use our own occupancy,  temperature, and humidity sensors - along with programmed schedules - to control the HVAC in our properties.We're dealing with predominately student rentals, not vacationers, so our principal concern is with enforcing upper and lower hard-limits on the temperature and knowing if windows are open while the system is being called to provide heating or cooling.

I'm in NOLA and it is brutally hot and humid here in the summer, so I've always attributed the difficulties to that. 

As the humidity is getting higher outside I have noticed the spots all sweat (moisture seems to condense on them.

In Houston, where summers are extremely hot and humid, Andy Teas, Vice President of Public Affairs for the Houston Apartment Association, a trade association representing property owners, management companies, developers, and other related professionals in the rental housing industry, says "virtually 100 percent" of apartments come equipped with central air conditioning. 

I do know that many were built in the north, that used materials that when exposed to hot-humid FL summers, will emit noxious fumes.

@Christian Podedworny how doe you deal with extreme weather conditions such as Arizona heat or metal corosion due to Florida salty humidity?

I had one floor that was so bad the carpets and padding had to be removed then I had to seal off the subfloor/plywood with BIN Primer then lay out a thick plastic sheeting then install new padding and carpet.If you dont neutralize the source of the odor every time the carpet gets wet or damp from humidity it will smell again.

"humidity is 200%"..loli lived in florida for 8 yrs, i know how that feels..