A structure having a confined space. The structure includes: (a) a first building unit, (b) a second building unit, (c) a confined space located between the building units, and (d) a structure connecting the fire resistance rated, confined space to the first unit and the second unit. The confined space includes: (i) an interior support structure, (ii) an outer membrane on each side of the interior support structure, (iii) a substantially organic material between the outer membranes, and (iv) at least one secondary support member attached to the interior support structure for preventing bowing of the outer membranes. The confined space provides fire, sound, or thermal resistance and combinations thereof.