Sealable ceiling assembly

A sealable ceiling assembly is provided for use in applications such as clean rooms. The sealable ceiling assembly may include main beams suspended from a support ceiling parallel to each other and cross beams that run perpendicular to the main beams to attach the main beams together. Each cross beam has a bore from which coupling members extend to either side. Each coupling member has a head with a cam surface designed to interlock with a retention slot of the main beam in response to ninety-degree rotation of the coupling member. The coupling members are attached within the bores of the cross beams via set screws that can be rotated after engagement to urge retraction of the coupling members into the bore to tighten engagement of the cross beams with the main beams. Stiffeners may be attached to top nut slots of any of the beams that need reinforcement.