In my experience, if you are using a general contractor or even any trade contractors, you must specify every detail that you want. If you don't they will bid on and install either the product(s) and workmanship they are used to installing or the cheapest on the market to keep their bid down. The plans should cover all the details of construction, and a separate specification sheet should cover special installations, equipment and materials for each trade. This is how architecs do it.