Water leaking into house through sliding glass door, could missing flashing be the cause?

Question

Newly renovated house, after the last big rain here in Arizona, we noticed that our sliding glass door let water into the house. It appeared to come into the tracks somehow, but I emptied 5 gallons of water on to the tracks outside and nothing came in. I spoke to a door guy at Home Depot who just so happened to be hanging out and he said he was certain that the issue caused by not having a flashing installed under the sliding glass door.

Does this sound plausible? How would flashing keep water out of the house?

I did notice that our patio got flooded when the water seeped in, but it didn't seem high enough to go up through the track and leak into the house.

Answer 1

Since you have poured water onto the tracks and no water leaked inside; check a few more things. I don't see a gutter above the door. Use a step ladder and run some water from a hose onto the roof, downward toward the door. The water could be lipping over at the edge, into your soffit, across the top of the door and then down the sides onto the floor. Remember, water takes the path of least resistance, so it could be leaking into the soffit from somewhere other than at the doorway. Also check both sides of the sliding section of the door for any cracks that a side wind could blow water through. I would also suggest caulking that large crack across the bottom of the door...

Answer 2

"...it didn't seem high enough to go up through the track and leak into the house."

I believe the flashing comment implies that the HD guy was concerned about exterior water flood coming under the track, rather than through or up and over the track. I think it is likely that is exactly what happened, judging by the height of that slab patio, and I don't think any flashing would prevent it. You may want to cut a drain channel across that door and sidelite span.