Outdoor dew points at Sea-Tac average about 53°F in August, only a couple of degrees below a 55°F cellar; if the house air carries similar moisture, the room-side face of thin, cold glass can approach the fogging point. Insulated glazing keeps it warmer. With only around two days a year at 90°F or above on Sand Point normals, the bigger cooling question here is the glazed area and the sun the room gets, rather than outdoor heat.
Inside city limits, Bellevue asks for a permit when a remodel creates new walls or turns a basement into living space, and when circuits are added or moved; the city also issues its own electrical permits rather than leaving them to Washington L&I. A new glass room with its own circuit can therefore involve building and electrical permits; how the city treats the cooling equipment is something we confirm with Bellevue Development Services for each project.