Traditional installations of base isolation can be expensive, especially in retrofit applications. Addition of a rigid diaphragm above the isolation layer, excavation of a seismic moat, and extensive foundation work increase construction time and costs. As a result, isolation retrofit projects are typically limited to buildings with historic significance and large budgets. Limiting the use of isolation to new and/or large budget structures means fewer buildings are likely to remain functional post-disaster, decreasing community resilience during large earthquake events. To make isolation retrofit accessible to a wider range of structures, the up-front costs must be reduced. This can be achieved by placing bearings on column tops, forgoing the need for construction of a seismic gap and an additional rigid diaphragm. However, columns under the isolation layer may be flexible, changing the traditionally assumed bearing end conditions. To assess the viability of column-top isolation, the performance of a pre-Northridge steel moment resisting frame office building, designed to the 1965 National Building Code of Canada (NBCC), is compared against a column-top retrofit with stiffened first floor columns and a traditional base isolation retrofit design using lead-core rubber bearings. This study also explores the impacts of gravity frame modelling assumptions in moment resisting frame structures on the performance of the isolated systems. Suites of ground motions representing different fault types were selected and scaled to hazard levels prescribed in the 2015 NBCC. Using a nonlinear time history analysis in OpenSEES, the overall seismic performance of column-top isolation was investigated.