Forming part of what is known as Brentford's "Golden Mile" business area; Great West House with its L-plan design is an iconic 1960s tower. Known as GW1 and GW2 the paired buildings are owned by commercial property investment company CLS Holdings plc and operated by Instant Office Ltd. as a Business Centre providing fully furnished office suites, conference rooms, catering and leisure facilities. An extensive programme of refurbishment and upgrade has ensured that the buildings provide contemporary accommodation to a high standard. However, with energy performance now assuming greater importance for building owners and managers the original metal windows are also being enhanced to improve standards of thermal insulation and comfort. The chosen solution was Selectaglaze's bespoke secondary glazing with high performance seals which reduces heat loss by more than 50% and minimises air leakage. Comfort is improved and energy demand reduced.