Presidio Chapel Historic Structure Report - Presidio Trust

PRESIDIO CHAPEL (BUILDING 130)SAN FRANCISCO, CALIFORNIAOffices, Corridors etc.For most of the remaining occupied spaces, either a carpeted floor or asuspended acoustic ceiling should provide adequate control of occupancysounds. Room-to-room sound isolation can be attained by use of a full-heightpartition as noted for the library, but a single layer of gypsum board each sideshould meet most office privacy needs.Blower RoomFor the blower room, the wall on the activity room side should be full-heightsteel studs with double 5/8’’ gypsum board each side, 3-1/2” fiberglass batts inthe cavity, and all joints caulked airtight (see Figure 2). It is important to avoidany contact between the blower unit and the walls, and the entire blower-motorsystem should be resiliently supported on neoprene isolators such as MasonIndustries type ND selected for a static deflection of 0.50 inches. On the doorside, the infill wall should be the same stud construction. The door should have asound isolation rating of at least STC 40 with heavy-duty, adjustable-edge gasketsand grout-filled steel frame. Suitable doors are supplied by Krieger, Overlyand others (see Sweets). The only ventilation to this room should be via anacoustically-lined duct, preferably from outdoors. For the ceiling of the blowerroom, a 1-1/2” to 2” thick layer of fiberglass board with a density of at least 3lbs. per cubic foot (i.e. not batt insulation) should be installed on the ceiling. Thiscould be either a finished material such as Armstrong “Nubby” or an industrialfiberglass board such as supplied by Johns-Mansville, MBI, and others.Interior Acoustical Treatment of ChapelFor the nave, we recommend keeping changes to a minimum because the presentacoustical quality of this space is known and liked. We recommend that eventsother than worship and celebration be accommodated by the installation of asuitable speech amplification system but that these be considered secondary inacoustical importance. For the chancel, however, we recommend incorporationof some shaping modifications which could be either added onto the existingsurfaces or recessed into these surfaces to enhance scattering and diffusion andto improve sound projection from chancel to nave. Figure 3 shows a possiblemodification of the chancel wall surfaces. It would be desirable acoustically toeither revise the quarter-sphere form of the chancel or at least to modify itsacoustical characteristics by adding sound-absorbing panels to provide alternatingreflective and absorptive surfaces. This is indicated on our sketch and could beincorporated into the architectural design of the apse.For the organ grilles, we recommend removing the existing screens. They couldbe replaced by a less obtrusive, highly transparent-to-sound fabric such as aloudspeaker grille cloth, or you may wish to work with the organ builder ondeveloping facade pipes to make the organ a more positive element in the design.PART III: TREATMENTRECOMMENDATIONSPage & Turnbull83