Ground Level Deck Against House & Slab (roof, drain, molding)

[d2mini]

Hi all,

We just bought a house here in Houston that has this new-ish ground level deck which is right up against the house.
I've seen this kind of thing a lot down here especially where people are covering small concrete patios.
As you can see, the deck is pretty much level with the threshold to the french doors.
The only issue is that a piece of baseboard molding at the bottom of the door's frame INSIDE the house has some swelling from moisture. It's a square block at the very bottom of the door casing. So obviously some water has made it's way in.
Is this just a case of needing to seal the exterior with some caulk or something?
With putting a deck right agains the slab, is some kind of flashing needed?
I haven't moved in yet so I haven't yet been able to investigate if any kind of flashing currently exists.

Thanks!

[K'ledgeBldr]

If I had to guess- the door units were not properly sealed under the threshold.

As a general rule you wouldn't have the deck flush with the threshold; it would be a 3-4" step down. This prevents water from penetrating at the threshold.

Is it catastrophic, no. Can it be corrected, yes. Is it worth it annually, no. Constant monitoring of threshold, weatherstripping, caulk, etc. just to be sure you're not getting saturated.

[harry chickpea]

Agree. It could have been driven rain that caused the issue, not the deck.

In Houston, I might consider extending the roof out to create a shaded portion of the deck to make it more useful in hot sunny weather. That would kill two birds with one stone.

[d2mini]

Thank you both.

harry, yes... eventually we will add some sort of overhang/covering.
We have also talked about adding gutters along the back roof line.

Also, some new info has been passed along... seems as though that particular door wasn't closing properly/tight enough at the threshold and is being fixed.

If looking at the first photo, you can see there is a small gap between the deck and the moldings.
Is this something you would caulk? Or does it need to "breathe" or allow water to run under and drain down?

[K'ledgeBldr]

Gutters will probably help more than anything else! All that rain running off the roof, splashing on the deck, and onto the door, threshold, etc.

Obviously, the door units are not original to the house. So, whatever was done to accommodate the units could also effect weather tightness. Personally, I think I would return to the 4-panel sliders that were probably there originally.