from a buffalo ny landlord who has asthma and is allergic to house
dust:
both answers are correct subject to the insulation, vapor barriers,
design of the house, and the temperature and humidity at the moment of
giving the answer.
upset tenants won't pay rent, let them out of the lease before they
move in and tell them they should have any dwelling inspected before
they move anywhere to be considerate of their medical requirements.
depending on the seasonality and severity of allergies they could be
allergic to a piece of new carpet or even peanuts in the bird feeder.
buy out your brother-in law. rental home ownership cannot survive a
partnership except with your wife.
here, people move in summertime. i know how extreme it gets inland in
ohio, i've visited there summer and winter.
re-advertise that air conditioned house, new tenants will be more than
happy to move into a 1970 home with ice cold air conditioning available
to them.
wonderful info and technical stuff at:
http://www.buildingscience.com/resources/homeowner.htm