A service page that actually ranks needs more than a paragraph describing what you do - it needs real, specific content: the process, typical cost ranges, a few real project photos, a location-specific mention of where you work, and answers to the two or three questions homeowners most commonly ask about that service.
The length that tends to work well is 600–1,000 words - enough to genuinely answer the questions a homeowner has, not padded for the sake of length. A short, thin page and an over-long, repetitive one both underperform a page that simply answers the real questions clearly and stops.