It does sound like you have a good relationship with your dad.

He's just concerned that weed will be something that'll interfere with your success and/or ambitions. Dads are that way. They want the best for their kids. They want their kids to rise to that challenge, too, and be the best they can be.

If your grades are good, you're keeping up with your responsibilities, maintaining a social life, and weed isn't your sole source of pleasure in life, you and your dad may just have to disagree. The bottom line is it IS their house. They pay for it and let you live in it. So hard as it is to hear, you do need to abide by their rules till you're out and on your own supporting yourself. If that's an impossibility, I'd keep the amount of your smoking on the down-low and make damn sure it didn't interfere with your life, your plans, your grades, your jobs. While you're at it, start educating your dad about cannabis. Start here(scroll down to general information and check out those links).
Erowid Cannabis (Marijuana) Vault