In assisting architects and designers on their projects, we have seen many ceilings with soffits lately and wanted to offer a couple of design solutions. Quite often these ceilings need to meet a certain fire and acoustical rating, and these assemblies can create some hurdles. The assembly designs shown below are two approaches to achieving both the acoustic and fire requirements.
Soffits in RSIC-1 ceilings
Drawing #2 has a fully isolated ceiling on spring hangers that runs continuously with the soffit framed below the spring-hung ceiling. To meet both the acoustical and fire ratings, the primary ceiling should have no penetrations, and this will achieve the best acoustical result.
First the ceiling is framed out complete. Next, attach the sound isolation products(RSIC-1 isolation clips and 25 gauge, 18 mil furring channel shown)to the framing. L metal is used to make horizontal to vertical transitions. RSIC-1 clips can also be used on the vertical plane of the soffit frame if the L metal method is not desired. This is the suggested approach when using the RSIC-1 clip as your primary isolation method. Acoustical caulking is applied at the intersection of the soffit drywall and the adjoining wall. Meeting the fire requirement may require pre-rock in the soffit. Because requirements for ceilings can vary from jurisdiction to jurisdiction, please check with your local officials for details.
Soffits in Spring hung ceilings
Drawing #2 has a fully isolated ceiling on spring hangers that runs continuously with the soffit framed below the spring-hung ceiling. To meet both the acoustical and fire ratings, the primary ceiling should have no penetrations, and this will achieve the best acoustical result.
When ceilings require the higher acoustical performance provided by full spring hangers and include soffits, the soffits can be fastened through the gyp ceiling into heavy gauge hat channel (20 ga min. to prevent the possibility of fastener pull-outs due to the concentrated additional loading created by the soffit) In the system shown here, full springs support cold rolled channel framing with heavy gauge furring channel with two layers of gypsum attached to the furring. (RSIC-SI-CRC Ez full spring hangers shown). Adding spring, hangers or increasing spring strength can be used where needed to support the extra weight of the soffit frame and gypsum board. First a complete spring-hung ceiling is installed from wall to wall. Then the soffit is framed below the acoustical ceiling, using the spring ceiling as the supporting structure, Lastly, the soffit cavity is insulated, then finished with gypsum board. Acoustical caulking is applied to all intersecting perpendicular joints for both the isolated ceiling and where the soffit intersects the adjoining walls.
