Except as specified below, all operations shall be conducted entirely within a building or buildings fully enclosed on all sides. Not more than 1% of the entire area of the lot may be used for outdoor storage, provided that no part of such area shall be located nearer than one hundred fifty (150') feet to any front lot line and one hundred (100') feet to any side or rear lot line, and provided further that any such area shall be screened adequately to conceal entirely at all seasons of the year any stored items from the view of adjoining lots or streets.