Ivan Lyall Holmes (16 October 1920 – 26 August 1970) was a New Zealand structural engineer whose advances in concrete masonry building methods in the 1950s and 1960s were central to the avant-garde style of modernist architecture known as New Brutalism which emerged in the 1950s.
It was epitomised locally in the work of architects such as Miles Warren, Maurice Mahoney (Warren & Mahoney) and Paul Pascoe.
Holmes engineered many of Canterbury's first modernist buildings including the Dorset Street Flats, the SIMU building, the Students' Association building at the University of Canterbury, and the Christchurch Town Hall.
He also worked in Vanuatu (then called the New Hebrides) and the Solomon Islands engineering hospitals, schools, a Government House and a cathedral.
Holmes was 49 when he died during construction of the Christchurch Town Hall.