I'm about to start a comprehensive series of posts on the Petit Trianon utilizing drawings and my photographs; not all at once, mind you! What better place to start than the stairhall where any tour begins. Like many grand houses, the Petit Trianon is designed on a Piano Nobile layout. The ground floor is relegated to servants quarters (with the exception of the stairhall, guards room and a billiards room which all flank the courtyard to the bottom of the drawing). Above you see the ground floor plan.
The stair wraps the grand 2 story space and brings you up to the main floor above, which contains the entertaining areas as well as the primary bedroom and boudior.

This section shows the relationship a little better in blue. The main kitchen is the area on the ground floor with the large fireplace and the salon is above. The top floor were guest and servant bedrooms. I think the building is best understood here in section as it contains numerous floor and ceiling levels: not handicapped accessible!
The view above from the guards room, through the stairhall and into the billiards room shows the beautiful marble floors in the hall as well as the enfilade. The light was amazing in this space reflecting off the limestone walls, as it was within the whole house.
Stepping into the stairhall (along with the other tour members, it was crowded!) you notice the beautiful limestone staircase with gilded iron handrail. The symbols in the center portion are the monogram of Marie Antoinette. The low doorway (see the gentleman ducking) steps down into the kitchen.
The lantern crowns the space: I would love to see the room in the evening lit by it!
The doors and shutters are painted a light blue which adds some color to the neutral space.
I loved the juliet balconies and windows into the space, much like a courtyard. This one straight ahead opens into the private dressing room of the master bedroom.
A closeup of the railing where you can see the gilded monogram of Marie Antoinette.
A detail of one of the limestone brackets which decorate the room.
I'll end this first tour with some elevations, you should recognize them after the photos!
Next up, the billiards room!