An adjustable-height support member, also referred to as a chair, provides support in a panel assembly having an inner wall and an outer wall. The chair includes a base configured for attachment to an interior surface of the inner wall. A shaft extends from the base. An optional cap covers the shaft such that the total length of the chair corresponds with a desired thickness between the inner wall and the outer wall of the panel assembly. During assembly, the chair prevents sagging between the inner wall and the outer wall. The chair also allows the insulating foam to be applied so as to substantially fill the void between the inner and outer wall.