House breaking an apartment puppy?

I live on the 1st floor of a block with a green directly outside. It takes about 3 minutes to walk there. My french bulldog pup is 14 weeks old, I begun training him from 7 weeks on wee pads then when he had all his shots at 12 weeks to go outside. I take him out every hour and he is very good about doing his business. We are having few accidents in the flat as I take him out so regularly. When he does accident in the flat I scold him (but never hit). What I want to know is when will he will be able to communicate to me(by going to the front door) that he needs to go to the toilet. He is crate trained, although when we are in the same room together, the crate is next to my desk so I do not lock it. I only lock it when I go out shopping etc and his is fine. thank you