After the 1939-45 war, the old oratory, above the Junior School classrooms, could no longer accommodate the growing number of pupils (500 by 1950). Space had been set-aside for a College Chapel (at the insistence of the Provincial Council). Wartime restrictions as well as the shortage of money postponed the building of the Chapel. On becoming President in 1951, Fr. Joseph Gilmore began planning a development, which included, besides the Chapel, additional classrooms and a Science room together with an Art Room and accommodation for seven Community teaching personnel.

Architects made sketches of the new buildings in November 1951.  These were approved in March 1952, tenders were received in January 1953 and work started in April of that year. The estimated cost of the buildings was about £65,000. The Provincial Council contributed £10,000 and the College had £20,000 in hands for the project, leaving just over half to be gained by fundraising activities. The new buildings changed radically the skyline and frontage of the College, with the focus of attention moving from the Victorian façade of the original to the imposing new Chapel with its fine bell-tower.

The new Church is dedicated to the Immaculate Heart of Mary, Refuge of Sinners (Feast: 16^th January).  It was to the Immaculate Heart of Mary that Fr. Libermann had dedicated his Missionary Society. It remains the co-title of the Congregation of the Holy Ghost.  …This Church dedication is a reminder to all to turn to the Heart of Our Heavenly Mother as to a most loving and sure refuge.  We are reminded of this by the dedication of our Church (as is also the case with our Parish Church opposite the College).

An endeavour was made to plan the new church in keeping with tradition and simplicity. It consists of a rectangular Nave with circular apsidal end containing the High Altar. There are two side altars, one on each side of the circular headed Chancel Arch. There is an Organ Loft approached by a fireproof stairs from the School Corridor.  

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A rectangular Bell Tower has been constructed over this staircase, surmounted by a simple Latin cross in gold, its white granite stands out in pleasing contrast with the rustic brick and blue slate of the main structure.  It is an added embellishment to the Rathmines district standing as it does sixty feet high on the low rise above the main road and suitably set off by the stretch of green lawn in front.  There are two additional altars in the Organ Loft.

The windows of the Church are circular headed and glazed with leaded lights in which old Irish cross motifs from the ancient monastery of Clonmacnoise have been embodied.  Their height is noteworthy.

The internal walls of the Nave have been panelled to a height of eight feet with mahogany, over which they are finished in plain grey plaster. Confessionals are included in the general panelling scheme at the back.  The seating is also in polished mahogany.  The ceiling design consists of coffering which enhances the appearance and has definite acoustic value. Its height gives a feeling of amplitude to the Nave.

Teak block has been selected for the flooring with centre aisle and transverse aisle in Italian mosaics. Beginning from the back of the Church the three sacrifices of the Old Law mentioned in the Canon of the Mass – of Abel (a lamb), of Abraham (Isaac), of Melchisidech (bread and wine)- have been executed as subjects in mosaic insets of attractive colouring.

The simplicity, dignity and beauty of design are continued in the sanctuary which is executed in coloured marbles – black and gold in the risers of the steps, with treads in white and black Paranazzo.

Two pairs of marble columns bear up the High Altar. The altar table is a slab of beautiful black Kilkenny marble, weighing a ton and a half. The recessed frontal of rich onyx with its German Cross in white Carara marble as centrepiece, serves to make it the focal point of the Church. Candlesticks, Crosses, Tabernacles, Sanctuary Lamp and wall brackets for lights – all of polished bronze – complete the harmony of design.  Externally the Church is faced with red brick, with granite dressings to the windows, quoins etc.  The roof is covered with Killaloe slate.