The roof of the building is to be covered with slate [preferably red], laid on terra-cotta and supported by iron trusses and beams; the iron-work to be protected by a fireproof covering. The tower roofs contemplate granite, lapped and jointed so as to be weatherproof, laid on iron beams and supported by iron trusses. If a cheaper covering is desired, slate or tile can be used without affecting the design.
The ceiling is a barrel-vault with large and small arched ribs pierced in each bay by the small vaults in which the clerestory windows open. It may be treated in one of three ways: first, finished in marble; second, marble ribs, the larger surfaces being terra-cotta blocks covered with mosaic tile; third, the larger surfaces frescoed on plaster. The ceiling of the lantern in the centre of the cathedral will be supported by arch trusses, and show metallic ribs on the interior, glazed with cathedral glass.
The screens between the choir and aisles and between the aisle and vestries and chapels are intended to be of wrought-iron, bronze or brass, or a combination. They should be arranged so as to slide down into the cellar and leave the entire building open and unobstructed whenever it might be thought desirable.
The outside doors are to be bronze, with figures on them in low relief.
The size of columns and piers, and the weights imposed upon them, the thrusts of arches and trusses, their proper abutments and ties and other constructional problems have been calculated with a sufficient degree of accuracy to determine the feasibility of the execution of the design according to the drawings.
In the lantern where the frescoing is contemplated the wall will be faced with porous brick, on which the proper fresco plaster can be spread.
The plan is arranged to facilitate the ingress and egress of large assemblages of people, five doorways being provided in the nave entrance and two in each of the transepts. The galleries over the nave and transept vestibules and the triforium have stairways with entrances on the side porches. Including the clergy entrances, fifteen outside doors are planned. The vestibules and porches connect with each other so that worshippers can pass from one to the other under cover.
The arrangement adopted for the central tower allows a central auditorium about one hundred feet in diameter, unobstructed by columns or piers, with the nave transepts and choir opening into it. The aisles are not decreased by this central enlargement, as they deflect through the four abutting towers.
The different vestry-rooms, library or sacristy and the treasury are grouped conveniently to the choir, with separate entrances for the church officials. The meeting-room for the clergy or chapter and the chapel have entrances independent of the church, or by lowering the screen they can be thrown open into the cathedral. Toilet-rooms, custodian’s and a committee-room are located on the transept vestibules, as these entrances would most probably be constantly open.
Elevators are placed in two of the supplemental towers, and stairways in the ones adjoining the choir, landing visitors on the triforium gallery, which encircles the building, and in the two galleries which encircle the central lantern. From the lantern galleries visitors can obtain fine interior views of the building, and comprehend the crucial form of the plan at a glance.