how much clearance should be between top of bathtub door and ceiling?

Question: We're installing a sliding bathtub door. Do we need a gap between the top of the door and the ceiling of tub area? (if so, how much?)

If there's little or no gap, will moisture cause damage inside the tub area (if there's no place for the steam to escape while one showers for example)?

We previously used a shower curtain. Our bathtub/shower area has a very low ceiling so that the height of the bathtub door we bought (it is standard height, nothing special) will come very close to this ceiling, probably within an inch. When we view the photos of other similar bathing areas, there is always a big clearance between top of bathdoor and ceiling of bathroom, because most people probably have the same height ceiling in the bathroom and in their actual bathtub area. But ours is an old house and above the ceiling in the bathtub area is some plumbing to the 2nd floor... we have the wall opened & the ceiling above the tub could probably be raised a bit more if we wanted.. However we don't think its necessary, but are wondering the advantages and disadvantages of doing it either way and are not real sure what is best to do.

It is not unusual to install tub or shower enclosures right to the ceiling. True it will be a little steamy in there, but the secret to any bathroom is good ventilation. I always insist on much more than what would be considered minimum. Just be sure to leave the doors open after shower so it can air out.