Flush Saddles at Floor Joints

In buildings other than theaters the standard transition between floors made of different materials is a raised saddle. Raised saddles are also used at some doors and expansion joints. Usually the saddle is a metal bridge -- often an aluminum extrusion -- that sits over the joint between adjacent floor materials. Occasionally saddles are made of other materials, such as wood or marble. Raised saddles stick up a fraction of an inch above the floor surfaces on either side. This standard raised saddle detail is unsuitable for any location in a theater where pianos, wardrobe racks, scenery, road boxes, and other units on casters are rolled in and out. For example a change of floor material is often needed between the stage and the backstage corridor, and again between the corridor and the scene shop. An architect might normally detail each change of material with a raised saddle. In locations in a theater where rolling equipment is used raised saddles should not be used.

Raised saddles are unsuitable for two reasons. The increased effort to hump rolling freight over the saddle is a nuisance. The noise generated when anything rolls over a raised saddle is unacceptable in a performance environment. Everything in the theater moves on casters. Everything should roll over floor joints smoothly, as if nothing is there.

There are several alternative details suitable for use in theaters. Among these solutions are: a flush hairline joint with no saddle; a flush gap joint with no saddle filled with standard joint filler; or a steel plate saddle that is recessed flush with the floor. The plate saddles are detailed "heavy duty", as they would be for an industrial environment, which is actually the case. Joint design is made more complex by three related issues.

1. The wood stage flooring expands and contracts horizontally as the air humidity changes. The stage floor needs room to move at joints with adjacent floors.

2. In some theaters the stage house structure is isolated acoustically from the adjacent parts of the facility. High values of acoustical isolation require that the stage is built as a separate structure -- in essence it is a separate building. Floor joints at the perimeter of an isolated stage are expansion joints that have acoustical isolation value. Sometimes the acoustical doors align over the saddles, which makes sealing the acoustical doors airtight to the floor very difficult.

3. The stage and the adjacent building structures can have different heights, weights, and foundations, leading to differential settlement. When differential settlement occurs the saddles become small ramps between adjacent floors at different elevations.

At several times during the preparation of the contract documents the design team should review the likely path of rolling equipment in the building. Doorsills, expansion joints, acoustical joints, changes of floor material, and all other floor joints in those paths should be checked for appropriate flush joint details. The floor detailer, spec writer, acoustician, and door detailer should all be made aware of the requirement for flush doorsills.