Can a flat follow Vaastu if the building already exists?
Yes. The building fixes the outer walls, and the consult works inside them. Facing, the bed, the kitchen use, and the entrance are still readable on a flat plan.
Vaastu for the home you already live in
Flats and houses are read the same way: entrance, kitchen, bed, and the weight of each side. When the walls should stay, the consult turns to placement and colour.
Home Vaastu
The rooms a family lives in: entrance, kitchen, and bed, read for a quieter day.
Renovation and land
A plot or a renovation, set on paper before a wall makes the change expensive.
Astro-Vaastu
The plan of the rooms, read together with the birth chart when you want both.
Questions
Where should the bed head sit inside the bedroom?
Place the head toward the heavier side of the room, usually south or west, with a solid wall behind it. Leave the lighter side of the room clearer if the plan allows.
When is colour enough, and when does the plan need a change?
Colour and placement are enough when the room is already in a workable direction. A plan change is for a kitchen, a bed, or a door that fights the rest of the drawing.