Vented gas cap-- ok in garage that is under the house?

I live in a ranch style house which means that part of my basement also serves as the garage. This is fantastic in the sense that the garage is basically heated...but there are some obvious worries here too.

So I believe that in almost any case, there will be some fuel vapors escaping from a car with gasoline in it...but I'm wondering if a vented cap (in lieu of the carbon canister) might present more danger.

When doing the motor swap in my car, the canister came out and I plugged off the line. Now, I'm in a situation where out of habit I pop open the gas cap every time I stop driving to relieve the pressure...not ideal of course but at least the fumes are contained when the car is parked since it's essentially "in the house." Before I order up the new cap, is correct that a temperature change in the garage cause a build-up of pressure and subsequently, a release of fuel vapors...into the garage?

...Or am I overestimating the danger here?

Thoughts are very welcome.