We are building a backyard studio and the windows and 12′ patio slider will be installed this week. Most of what I have read about window and door install indicates flashing the sill, ideally with a metal/pvc sill pan for water management. 

The door is to be installed 6″ above grade on a concrete slab and will have a step down to grade. I have been confused about what people do to cover the flashing on the concrete that is supposed to overlap the slab 2ish inches at the front if there is no metal sill pan.

My siding contractor mentioned that often people put the slider directly on the concrete and just flash the framing. He is willing to create a metal sill pan and flash for me, but wondering if maybe I’m overdoing it. The window company didn’t seem overly concerned about my request for a sill pan and said that it’s not done in our area often (Southern Ontario). There is a 2′ overhang as well.

Also, I will add I was told the “patio door sill has built in drainage and is designed to shed water to the exterior.” 

So question one, am I being extra and should forgo flashing below the door and just waterproof the framing and have it sealed along the back? It is a vinyl frame.

Edit to Add: Is there an issue with putting flashing on the concrete because then vapour can’t escape like a sill gasket? He was going to use Zip flashing tape.

Attached are 2 photos, one from the outside before the PT wood was cut down and from the inside after framing.

Thanks for your expertise.