patio
I am not sure if the sand was washed away by the water that is going under the patio in that corner or the bedding material is simply missing here. The paver below is from the left circled area in the second photo. That corner is actually raised a little bit which is the opposite that should happen if the sand was washed away from under the paver. So …what material was used for bedding here? Can I say that the bedding is missing?
Two questions: 1) Where does the water come from? And, 2) Where else could you send it?
First thought is that you may need to do some grading and/or install some sort of french drain system to help that water run off to somewhere else... or perhaps intercept it before it gets 'cornered' if possible. Also, those edgings around the patio appear to stand a bit above the level of the patio itself... if I'm seeing that right that can't be helping.
Hard to say much more without a broader sense of the lay of the land. Again, the water needs to go somewhere, and that's the first decision.
far as the low spots in the patio themselves that may just be the result of some settling if the material beneath wasn't perfectly compacted. So you might pull up the low-lying bricks and tamp in some additional sand to get those spots up to grade. You might also consider a narrow gutter around the edge to catch water and direct it somewhere away from your wall. Again, much depends on the overall grading of your lot.
If you're going to pull up pavers to install a french drain, you might as well just pull up all the pavers and get the slope correct instead.
A well laid patio should naturally shed water via its pitch. The ideal solution is to pull up the pavers, re-grade the base layer (should be sand directly under the pavers) and then lay it all back down...perhaps with a slightly exaggerated pitch this time.
If you insist on a drain, I wouldn't bother with a french drain and instead consider a surface drain:
It'd be a lot easier to install.
Best Answer
It's hard to tell from the picture but it may be -1/4" crushed gravel that was used as bedding. We used that quite often in place of a mortar type sand because it didn't compress as much but still allowed easy grading and workability.