This paper investigates the potential involvement of epistemic uncertainity in mediating between complex design requirements and strategic switches in software design strategies The analysis revealed that the designers produced an initial fist-pass solution to the given design brief in a breadth-first manner with this solution addressing several easy-to-handle requirements The designers then focused on adding relatively complex-to-handle requirements to this initial solution in what appeared to be a depth-first manner as reflected for example by detailed mental simulations that spanned many transcript segments Fin them more such depth-fist development of complex requirements was linked to increases in epistemic uncertainty a finding that supports the predicted mole of uncertainity in mediating between complex requirements and depth-fist design Overall these findings support a view of software design as involving a mixed breadth-fist and depth-first solution development approach with Strategic switching to depth-first design being triggered by requirement complexity and being mediated by associated feelings of uncertainty (C) 2010 Elsevier Ltd All rights reserved