If the TOTAL pressure outside were higher, then there would be a net
force pushing in on the walls of your house. That's not easy to
maintain, since air would leak in an make the pressures nearly equal.
It sounds as if you are asking about the partial pressure of
water, whether it is different inside your house from what it is
outside. The partial pressure of water is just the amount of pressure
there would be if you took away all the molecules in the air except the
water molecules, keeping the temperature the same. The "vapor pressure"
of water is the partial pressure of water that liquid water is in
equilibrium with at a particular temperature. Water molecules evaporate
and recondense at the same rate when the liquid is in equilibrium with
the water vapor, and the amount of water vapor in the air needed to
make the recondensing rate the same as the evaporation rate depends on
the temperature and on nothing else. So literally, your question is
asking "if the temperature is higher outside than it is inside...".
This is an interesting question, because if there is a lot of water
nearby (lakes, oceans, soggy farmland after a rainstorm...) which is in
equilibrium with the water vapor in the atmosphere, then the humidity
outside is very high. Bringing humid, warm air in contact with colder
surfaces will cause condensation ("dew"). Condensation is a special
problem with air conditioned environments -- the water has to be
disposed of, or it can seep around, causing mold and mildew to grow
If there is no active cooling or dehumidification in your house,
and the partial pressure of water vapor is higher outside than it is
inside, then the water vapor will simply diffuse through the cracks in
the house and the humidity (and temperature) inside the house will
gradually settle into equilibrium with the air outside.
Mike W. and Tom J.
(published on 10/22/2007)