72. Level Ceilings

When there is a gallery in the church, thus necessitating high walls, a sufficiently high ceiling is usually afforded by using trusses with horizontal tie-beams, with the ceiling joists resting on top of the beams and spanning from truss to truss. By placing a cove at the juncture of the walls and ceiling the apparent height of the room is increased and the appearance and also the acoustic properties improved.

It is usually very much cheaper to support the roof and ceiling in this way, because simple trusses may be used, generally without very large timbers or rods, and very little finishing lumber is required.

As illustrating the method of supporting a roof and level ceiling over a crossing with four gables, Fig. 168 may prove of interest. This and the plan, Fig. 169, also show how a cruciform roof and exterior may be placed over a rectanglar building or room, the plan being a portion of that of the church shown in Fig. 167, while F'ig. 168 shows the actual construction of the central portion of the roof. The building being built on a narrow lot and it being desired to utilize the entire ground space (in width), it was necessary to plan the building in the shape of a simple rectangle, only very shallow recesses being permitted on the principal side and none on the other.

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Fig. 168.

By means of two posts, which were also utilized in supporting the gallery, the width of the main roof was reduced to 36 feet, and by placing shed roofs with the cornice slightly depressed over the spaces H, H, the appearance shown in the half-tone illustration was obtained. The central portion of the roof is supported by three trusses, B, C, F, of exactly the same outline, and by two Howe trusses, D and E, which are supported at one end by the wall and at the other by truss C, the members of the latter truss being made larger than those of trusses B and F on account of the additional loads, although only 10x10-inch timbers were required. The tie-beams of trusses E and D were framed flush with the ceiling joists to form a square panel in the centre. The top of these trusses come on a level and in line with the upper purlins, so as to receive the common and valley rafters. The inner end of the purlins extending from trusses B and F to trusses D and E are supported from the tops of the latter by stirrups. The inner ends of the lower purlins, which support the valley, are supported by braces from the tie-beams.of the trusses. The tops of the two posts have heavy cast-iron caps, with a flat top. In any roof construction the purlins should be well tied together endways and securely anchored to the walls.

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Fig. 169.

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Fig. 170.

In the church above illustrated the pulpit was placed where shown on the plan, and, although the room is rather long for the width, the acoustic properties both for speaking and singing, appear to be perfect.

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Fig. 171.