Most homes are still not built with a solarium as part of the plan, unless it is a custom home. Sunrooms are usually additions built onto an existing home and they are relaxing places, casually decorated, allowing sunlight to flood the room with lots of glass and windows. These rooms can run the gamut from their specific design, however, as the standard of what makes a sunroom is completely up to the homeowner.
As an example, someone might want their garden room enjoying the sun in three seasons, but perhaps not winter. Their sunroom may consist of a sturdy frame with almost all glass as protection from the elements. They don’t use the sunroom in winter because it gets too cold. However, another homeowner may want to use their patio room year ‘round as a place to relax, read, and entertain. Their sunroom may have higher walls with just the top frame as the glass element, or perhaps a completely framed room with lots and lots of windows. It really depends on the homeowner and what they intend to use the space for.
Many gardeners use their solariums for year-round cultivation and so heating and air-conditioning are secondary to the quality of light. Another use for the sunroom may not be for the sunlight at all (although that is nice!). A garden room can be used for lots of hobbies and other activity, such as a room for your treadmill or stationary bike. Or it could be a room that provides inspiration for painting or writing. Like man caves and billiard rooms, there simply is no strict definition of a sunroom. The beauty of this space is in the eye of the homeowner.