I've ordered and received a new custom pre-hung deck door. It's presently in my condo hallway.

My deck is on a flat rubber roof which got installed just this past summer. Below the roof are two floors with a condo on each floor. I'm on the third floor which is the top floor.

Since we've already had one leak issue with this new rubber roof (during this crazy Boston winter which has dropped an amazing amount of snow), I really want to make sure that this deck door is installed correctly.

The roofer who installed our new deck roof and also built the 3 decks in our building, came by yesterday. He said if I want to install a new deck door, I should have my carpenter remove the present old door then call him (roofer) so that he can come and flash the area where the new door frame is going to go. He said that if my carpenter does his own flashing, the warranty on the deck roof will become void.

I therefore want to make sure that this new deck door is installed correctly.

I would really appreciate any advice I can get. For starters, I'm assuming that since my new deck door comes with its own aluminum threshold, the present wooden threshold can be removed? Am I correct?

In order to help you see what I'm trying to do, I'm attaching some photos.

Thanks!

My present deck door: