I was asked recently about how big does an attic hatch need to be.
The answer is clearly stated (as clear as it gets) in the Ontario Building Code (above).
For a single family home the typical size is defined by the ceilng framing at 24" on center leaving a MINIMUM finished opening of 21 1/2 wide by a 24" long.
If you ever think you' d like to go in there then make it 30" long.
