Try not to get too hung up on the actual profile of the window frame - and, honestly, you almost never have to understand how the window system actually manages water to detail it properly. Nine times out of ten it's safe to just assume that water can now - or someday will - move around within the entire depth of the frame. Practically speaking, this means:
1. Protecting the opening that you install the window in by fully covering it with self-adhered or fluid membrane on all four sides (our recommendation) or just at the sill and 6 inches up each jamb (the minimum requirement of most manufacturers), and,
2. Providing two full-perimeter seals around the frame:
an interior "primary" seal(caulking), and an exterior water-shedding seal(caulking) that drains (aka "weeps") at the sill. This is a rough diagram of the concept-your actual detail will of course can be different, but it should be generally consistent with this concept: the opening should be protected, and there ought to be two perimeter seals.
Even well-made windows leak. This is why we protect the openings in the first place.Windows have a lot of complicated internal joinery that is difficult to seal even in factory conditions. These seals are exposed to stresses during transport, installation, and service and will fail over time.(Not surprisingly, the seals that are most exposed to the stresses of UV, heat, and water tend to fail fastest)
"That’s why we use only the highest commercial grade materials for seal!"
In conclusion the relevant question isn't really do windows leak? All windows leak. All of them. The relevant question is under what conditions will they leak? And how often might we expect the windows to experience those conditions in service? Perhaps the answer is: not often. And that's great!
By choosing Vanguard Caulking, you ensure the advantages of a flawless sealant application. However, drawing from our extensive experience, we regret to inform you that we often find ourselves addressing issues arising from the work of others.