Source: Secchi Smith Source: Secchi Smith Source: Secchi Smith Source: Secchi Smith Source: Secchi Smith Source: Secchi Smith Source: Secchi Smith Source: Secchi Smith Original details of Denys Lasdun's IBM headquarters AHMM has reworked its plans to upgrade Denys Lasdun’s IBM building on London’s South Bank for the second time in a year after the brutalist block won a grade II listing from Historic England. The practice’s original proposals for the office complex, completed in 1983, were floated early last year and envisaged the creation of an extra 20,000sq m of space through the addition of two new storeys.