What is the proper way to introduce or expand relative context to a question, answer, or comment?

For example, A person asks for the best way to caulk the exterior of the pictured window sill. A person gives an answer to the question (a sufficiently good answer). I see that the window sill was constructed incorrectly.

While the question was specific and the answer was correct for the question, I wonder what would be the proper way for me to bring up the issue of the sill, which neither the questioner or respondent has acknowledged is a problem, too?

Would explaining why the sill is a problem (and how to fix it) be an "Answer", a "Comment" to the question, or a "Comment" to the answer?

[Edit: Note, my inquiry is more to ask, "How to expand the initial scope of any question, answer, or comment by asking about or mentioning its context?"]