The second level looks modest on a plan. A little step, a little lounge area, a little dining area. The trouble starts when the actual dining set is not little.
Size the rooms before separating them
Draw each furniture group in use, with chairs pulled back and space to move around it. Then draw the transition between levels. If a level works only when the furniture is empty, it is too small for its proposed job.
A single broad platform can change from family meal to party without negotiating an internal stair. Split levels can make sense where the ground changes and each platform gets a distinct, well-sized purpose. The level change should answer something the site or routine actually asks.
Think about the frequent journeys
Follow the trip with a serving tray, a laundry basket, and a guest who finds stairs tiring. Consider how lighting and winter maintenance make the transition legible. Have the stair, landing, guard, and structural design checked for the specific project.
Trex’s design considerations discuss multi-level planning alongside circulation. They are useful design prompts, not Ontario permit drawings.
Keep one level if the second has no job
Our preference is one generous living area before several small ones. Add a second level when it follows the site or makes a separate activity work better. You do not need a change in elevation to distinguish a chair from a dining table; sometimes the furniture is already doing that work.