Wrapping trim

Should the aluminum wrap on window trim be caulked to the wallboard or left open? I examined an installation today where the old wood trim underneath was showing. Am I wrong in assuming poor installation and thinking the reason for wrapping is to prevent water entry ?

Your right about the reason for wrapping the trim. No wood should be exposed. I normally seal the aluminum to the outer edge of the wood trim, behind the aluminum. Some surfaces are virtually impossible to lay a nice attractive bead of caulking on, not to mention the color variations. I always leave the bottom "wrap" unsealed so moisture can escape. (seal it to the window, but not to the house). Hope that was helpful.

We caulk the window before wrapping most the time. We then put a relief bend in the wrap that butts the window. This will cover the caulk line and give a good finish to the unit. There should be no wood exposed at all. Usually someone getting carried away with their snips. We also caulk all corner joints and seal it to the sill cover. We leave the face of the brickmould open at the bottom for drainage if needed. We also seal the outside of the brickmould to the house. This is a very important place water can get in and run behind the siding. Stucco exteriors can be difficult for this kind of seal. We just try and seal anyplace water can intrude.