The Triplet (Gasholder Nos 10, 11 and 12), King’s Cross

Three conjoined gasholder guide frames at King's Cross, originally built between 1879 and 1880 to designs by engineer John Clark. The contractor was Westwood and Wright, working for the Gas Light and Coke Company. These frames replaced earlier structures from 1861, 1864 and 1867.

The guide frames were originally located at a gasworks about 300 metres to the south. They were relocated following the expansion of St Pancras Railway Station, when the gasholder tanks were buried or demolished and the bells destroyed. The frames were dismantled in 2001, restored by Shepley Engineers, and re-erected surrounding apartment blocks on the current site in 2018.

The three conjoined structures are constructed from cast-iron columns and wrought-iron girders. They are known as Gasholder Nos 10, 11 and 12, each approximately 33 metres high but of varying diameters and column counts: No 10 comprises 15 columns with a 40.8 metre diameter; No 11 comprises 16 columns with a 44.3 metre diameter; and No 12 comprises 13 columns with a 32.3 metre diameter.

Each guide frame comprises three circular tiers of cast-iron columns joined by horizontal lattice girders, classified as 'Type 15' in Tucker's typology of gasholders. The three frames are conjoined at the centre, with several columns shared between the respective structures.

The columns follow classical architectural orders. The lowest tier is in Tuscan order, the middle in Doric, and the topmost in a simplified Corinthian. Each column supports an entablature bearing the correct classical sequence of mouldings. The Tuscan tier supports a plain frieze; the Doric supports a triglyph; and the Corinthian supports a frieze with a dentilled cornice. Column proportions vary according to classical canon, progressing from the heavier Tuscan at the bottom to the lighter Corinthian at the top. The columns are made of shorter sections bolted together on the inside, with capitals and entablature blocks concealing joints at the head of each tier.

Oval cast-iron plaques at the bottom of the lower columns state the date each gasholder was first erected and subsequently telescoped. Attached to the inside edge of each column are guide rails for the roller carriages upon which the telescopic bells originally rose when filled with gas and fell when emptied. Several roller carriages have been retained and remain adjoined to the guide rails near where the frames are conjoined.

The columns are linked at the level of the entablature blocks by wrought-iron I-section 60-degree triple-warren lattice girders, fabricated from sections of flat plate and angle that are riveted together. The southernmost gasholder guide frame bears rosettes on its latticework. At the centre of the cluster is a triangular configuration where the lattice girders link the three frames.

The residential apartment blocks and communal courtyard structure completed in January 2018 are not included in the listing and are not considered of special architectural or historic interest. However, any works with the potential to affect the character of the listed building may still require listed building consent.