Before the patio...

One last pic - during construction. They tacked up a black fabric piece between where the concrete would be poured and the bay. The concrete sits about 6" above the bottom of the bay.

so the bay cantilvers out from the main foundation and is the fascia boards at the ends of the joists that form the backside of the concrete slab/stairs. I assume there is still a cavity space behind the stairs and below the bay (unless they filled it all in with concrete, too).

Can you cut throught he floor in the bay and repair and properly flash the patio from the backside?

I think if you start chipping the concrete stairs it might be difficult to pour a nice patch without really hurting the aesthetics. (i.e. matching the color of the concrete, cracks at teh cold junction, etc.)

There is a space beneath the bay, but it's partially filled in with crushed concrete. Going at the problem from inside isn't really an option (or at least I'd like it to not be an option) because inside the bay is tile floor that extends into the kitchen and dining room. One suggestion I was given was to cut out 4 inches above the steps all the way across, possibly try to chip out some of the rotted wood, but mostly just leave it there, put in a piece of cedar or PVC trimboard with flashing behind it, and then caulk it all in, prime, and paint. Is that a good idea? My hope is that once I stop the water infiltration from the step (if that's where the problem is - I assume it is), then I can just leave the rotted wood underneath to dry out and it won't be a problem. Thanks for your reply.

Just off hand, I'd say the bay is cantilevered floor joists with a rim board, then trimmed out.

It's a really beautiful patio design, unfortunately with the concrete going above the wood, makes it a poor design.

Sure wish I could give a simple fix solution, but it appears it's going to take some redesigning. I won't go into the should have done aspect, since it's too late.

Good luck.

Thank you for the responses. I was giving this some more thought and am thinking of removing the rotten trim and then flashing and retrimming (keeping a good eye on the caulk bead over the years). My thought is that if I can keep water from seeping down the wall and getting behind the patio (between the patio and the wood) then I should be able to stop the water infiltration and thus, further rot damage. Does this make sense? Basically I'm not going to allow water to get between the patio and the bay. Any downsides to that? Would that possibly stop the problem?

I'm sure at this point, it's a do what you have to do.

I would also be concerned about the natural dampness, which occurs below the bay. It appears there is zero air circulation since the concrete is blocking the underneath.

Sooner or later, you're bound to see ants or such insects. At least you should know what they're after.

We had a similar situation where a concrete pad for a set of steps was poured against the front wall of the house, to above the concrete foundation level and above the sill plate that sat on it. There was originally flashing to keep water away from the join but over the years it corroded away and the water rotted out the sill plate. That and a couple of other pieces of bad design rotted out the entire corner of the house, which we had to have rebuilt.

While you might keep an eye on the flashing and caulking, how about future occupants of your house? Will the knowledge that this must be done get passed on, or lost? Caulk is not a long term solution.

One possibility for a long term solution might be to remove the concrete steps entirely, while keeping the patio, and build wood steps from the patio up to the doors.

I am also worried about your cantilevered joists. Did they put a vapor barrier down (like what you'd see in a crawlspace) to keep ground vapor from coming up and causing damage to your cantilevered joists?

(eee :/)