Original building (T-plan with facade to George Square), Robert Mathieson, architect H M Office of Public Works for Scotland, 1875-8. Rear elevation to Ingram Street extensively remodelled by W W Robertson in more elaborate style in 1892-4. Side elevations enlarging T-plan into present square and enclosing Robertson's work, by W T Oldrieve and C J W Simpson, 1914-16. All architects of HM Office of Public Works in Scotland.
Polished ashlar, channelled to ground.
George Street elevation: sober classical facade with Corinthian columned porches. 4-storey and attic with 5-storey end bays. 13-bays divided 1-4-3-4-1. End and centre 3 bays advanced and taller with projecting porches of paired polished pink granite Corinthian columns supporting mutuled entablature; round arched doorways with pilastered reveals and moulded archivolt, those to centre partly with modern glazing, to end bays astragalled fanlight or shell niche over panelled timber doors. All windows single light except at end bays tripartite. All windows architraved, round arched to ground, semi-circular pediments to 1st, consoled cornices to 2nd, lugged to 3rd. All sash and case with plate glass glazing.
Mutule cornice over ground, blind balustrading to 1st floor window cills, band course to 2nd cills with decorative incised detail. Deep bracketted eaves cornice with panel frieze. Balustraded parapet with intermediate die pedestals supporting urns. Advanced bays with pairs of tall square-section rusticated stacks, to centre these flank heraldic crest. Slate roofs, box dormers with small pane glazing.
South Frederick Street elevation: 15-bay, 5-storey and attic flank. Tripartite consoled door to right, 4 wide arched pends to left, 2 partly blocked. All single storey windows detailed as main elevation. Balustraded parapet with intermediate die-stacks.
Hanover Street elevation: 17-bay 5-storey and attic flank detailed similarly to South Frederick Street, 5 pend entrances.
Ingram Street elevation: W W Robertson 1892-4 central 5-storey 9-bay block. W T Oldrieve, 1914-16 outer bays. Materials as above, 3 and 5-storey Italianate facade, 17-bays divided 3-1-9-1-3. Outer bays detailed as above, inner 9 bays have lighter and more decorative nature. To inner bays 3 groups of 3 bays (flanked by recessed narrow bays) divided by pilasters and bands of vermiculated rustication. To 1st, tall arcaded round arched windows with column mullions, decorative sculpture in spandrels.
Pilastered windows to 3rd, all multi-pane casements with top hopper opening. Eaves cornice with heavy decorated consoles. Balustraded balcony to parapet. Flanking inner bays, tall round arched pend entrances with festoon decoration and panelled timber doors, good wrought-iron outer gates.