A demountable modular wall system including a series of individual glass panels that can be positioned adjacent to each other. Each of the individual glass panels is supported by a panel height adjustment mechanism that allows the height of each side of the glass panel to be adjusted. Each wall panel includes an upper trim section that is stationary relative to the movable glass panels. Each of the individual glass panels can include a stiffening channel to reinforce the vertical side edges of the glass panel. A vertical trim section can be attached to cover the panel joint between adjacent glass panels. A sliding door track can be attached to the top end of the wall panel to support a sliding door.